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Monograph
Systematic revision of the genus Peronia Fleming, 1822 (Gastropoda, Euthyneura, Pulmonata, Onchidiidae)
expand article infoBenoît Dayrat, Tricia C. Goulding, Deepak Apte§, Sadar Aslam|, Adam Bourke, Joseph Comendador#, Munawar Khalil¤, Xuân Quảng Ngô«», Siong Kiat Tan˄, Shau Hwai Tan˅
‡ Pennsylvania State University, University Park, United States of America
§ Bombay Natural History Society, Mumbai, India
| University of Karachi, Karachi, Pakistan
¶ Charles Darwin University, Darwin, Australia
# National Museum of the Philippines, Manila, Philippines
¤ Universitas Malikussaleh, Aceh, Indonesia
« Graduate University of Science and Technology, Hanoi, Vietnam
» Vietnam Academy of Science and Technology, Ho Chi Minh, Vietnam
˄ National University of Singapore, Singapore, Singapore
˅ Universiti Sains Malaysia, Penang, Malaysia
Open Access

Abstract

The genus Peronia Fleming, 1822 includes all the onchidiid slugs with dorsal gills. Its taxonomy is revised for the first time based on a large collection of fresh material from the entire Indo-West Pacific, from South Africa to Hawaii. Nine species are supported by mitochondrial (COI and 16S) and nuclear (ITS2 and 28S) sequences as well as comparative anatomy. All types available were examined and the nomenclatural status of each existing name in the genus is addressed. Of 31 Peronia species-group names available, 27 are regarded as invalid (twenty-one synonyms, sixteen of which are new, five nomina dubia, and one homonym), and four as valid: Peronia peronii (Cuvier, 1804), Peronia verruculata (Cuvier, 1830), Peronia platei (Hoffmann, 1928), and Peronia madagascariensis (Labbé, 1934a). Five new species names are created: P. griffithsi Dayrat & Goulding, sp. nov., P. okinawensis Dayrat & Goulding, sp. nov., P. setoensis Dayrat & Goulding, sp. nov., P. sydneyensis Dayrat & Goulding, sp. nov., and P. willani Dayrat & Goulding, sp. nov. Peronia species are cryptic externally but can be distinguished using internal characters, with the exception of P. platei and P. setoensis. The anatomy of most species is described in detail here for the first time. All the secondary literature is commented on and historical specimens from museum collections were also examined to better establish species distributions. The genus Peronia includes two species that are widespread across the Indo-West Pacific (P. verruculata and P. peronii) as well as endemic species: P. okinawensis and P. setoensis are endemic to Japan, and P. willani is endemic to Northern Territory, Australia. Many new geographical records are provided, as well as a key to the species using morphological traits.

Keywords

Biodiversity, Coral Triangle, Indo-West Pacific, integrative taxonomy, mangrove, South-East Asia

Introduction

Onchidiid slugs live in the intertidal, worldwide, except at the poles. Their larvae are released in sea water and, in that sense, onchidiids are truly marine. As adult slugs, however, they breathe air through a lung and die if they are immersed in water for too long. The slugs of the genus Peronia Fleming, 1822a are found across the entire tropical and subtropical Indo-West Pacific, from South Africa to Hawaii. They primarily inhabit rocky shores and coral rubble, can occasionally be found on muddy sand, but are typically not found inside mangrove forests.

The genus Peronia includes all onchidiid slugs with a dorsal notum bearing ramified appendages, or dorsal gills, which are most easily seen when animals are relaxed. Dorsal gills tend to be retracted when live animals are crawling at low tide, and they can be hard to see on specimens preserved without relaxation. In fact, Cuvier did not mention dorsal gills in the original description of Onchidium peronii Cuvier, 1804, the first Peronia species ever recognized. Dorsal gills were first illustrated by Savigny (1817: pl. 2, fig. 3.5) on a plate of gastropods from the Red Sea in the famous Description de l’Egypte, and first described by Audouin (1826: 19) in the explanation of Savigny’s plate. Dorsal gills are either present or absent on the dorsal notum of onchidiid slugs, and all slugs with dorsal gills belong to the genus Peronia (Dayrat et al. 2017: 1861).

For the past sixty years or so, authors have accepted only two valid Peronia species names for two species broadly distributed across the Indo-West Pacific (e.g., Solem 1959: 38–39; Marcus and Marcus 1970: 213–214; Britton 1984: 183): P. peronii (Cuvier, 1804) and P. verruculata (Cuvier, 1830). However, the differences between P. peronii and P. verruculata have remained unclear, to say the least, and both names have been used arbitrarily. More importantly, 31 species-group names are available for onchidiids with dorsal gills and their exact application has never been addressed. Indeed, the taxonomy of the genus Peronia is so challenging that people have avoided it for decades, and Labbé (1934a) is the last author who created species names for onchidiids with dorsal gills, except for the recent Peronia persiae Maniei et al., 2020a, regarded in the present work as a synonym of P. verruculata. The taxonomy of the genus Peronia is comprehensively revised here for the first time. The goals of the present revision are to determine how many Peronia species there are, where they are distributed, how they are related, how they can be identified, how many of the available species names are valid, and to create new names if needed.

All the available types of all onchidiid species were re-examined in the context of our revision of the whole family (Dayrat 2009; Dayrat et al. 2016, 2017, 2018, 2019a, b, c, d; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c), which served as a basis to establish a complete list of all the species names available in the genus Peronia. For the sake of clarity, important features (especially intestinal loops) of the types of Peronia nominal species are illustrated here. In many cases, lectotypes are designated in order to clarify the application of species names.

Fresh material was collected across the entire Indo-West Pacific, from South Africa to Japan, Hawaii, and eastern Australia. Special attention was paid to collecting fresh material from type localities. Specimens from which DNA could be extracted were also obtained from museum collections (the first author visited many collections around the world). Old museum specimens from which DNA could not be extracted were also examined, especially in cases of interesting geographical records or when specimens were included in important onchidiid studies (Semper 1880–1885; Plate 1893; Hoffmann 1928; Labbé 1934a).

Because they are notoriously cryptic, Peronia species were first delineated using DNA sequences. Then, the anatomy of the specimens was examined in order to determine diagnostic characters for each species as well as individual variation. As in our previous revisions (Dayrat et al. 2016, 2017, 2018, 2019a, b, c, d; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c), both mitochondrial and nuclear DNA sequences were used for species delineation and relationships.

Nine Peronia species are recognized here, five of which are new to science: P. griffithsi Dayrat & Goulding, sp. nov., P. madagascariensis (Labbé, 1934a), P. okinawensis Dayrat & Goulding, sp. nov., P. peronii (Cuvier, 1804), P. platei (Hoffmann, 1928), P. setoensis Dayrat & Goulding, sp. nov., P. sydneyensis Dayrat & Goulding, sp. nov., P. verruculata (Cuvier, 1830), and P. willani Dayrat & Goulding, sp. nov. Both P. madagascariensis and P. platei were only known from the original descriptions and are described anatomically in detail for the first time. Amazingly, the best anatomical description of P. peronii so far is Cuvier’s (1804) original description, but many traits are described and illustrated here for the first time. Finally, the anatomy of all mitochondrial units of P. verruculata is described in detail for the first time from numerous localities, although some anatomical information was scattered in the literature for three of them (units #1, #3, and #4).

These nine species cannot be distinguished externally, except for the very large individuals of P. peronii (longer than 100 mm). However, details of the internal anatomy can help separate species, except for P. platei and P. setoensis which are both cryptic externally and internally. Geographic distribution varies greatly among Peronia species. Three species are broadly distributed across the Indo-West Pacific, from the western Indian Ocean to the West Pacific: P. griffithsi, P. peronii, and P. verruculata. The six other species are characterized by much narrower geographic ranges. Three species are even endemic: Peronia okinawensis and P. setoensis are endemic to Japan, and P. willani is endemic to the Northern Territory, Australia.

Of the 31 Peronia species names available, four are valid and 27 are invalid: 21 synonyms (16 of which are new), five nomina dubia, and one junior secondary homonym. The large number of available names in Peronia is explained by a combination of three main factors. First, Peronia slugs have often been collected, because they are common across the Indo-West Pacific and because they mostly live in the rocky intertidal, which is more easily accessible than mangrove forests where most other onchidiids are found. Second, earlier zoologists created new species names without examining the types of existing nominal species and without proper knowledge of individual variation, which resulted in many names being added unnecessarily. Third, Peronia is a genus for which molecular data were critically needed, because species are externally cryptic; also, species could hardly be delineated just based on their internal anatomy because they differ only with respect to minute anatomical details. The fact that five new species names are needed in Peronia even though there already are 31 available names shows that a comprehensive revision was desperately needed.

Materials and methods

Nomenclature

Establishing a complete list of available names for a taxon often requires an enormous amount of time but it is the keystone of any taxonomic revision, because otherwise it would be impossible to address the nomenclatural status of available names and to determine how many new species names are needed.

All available type specimens were re-examined beyond the taxon of interest (Peronia) because species names often are incorrectly classified when they are first created. For instance, Onchidium durum Labbé, 1934a was originally created for slugs with a smooth notum, but the types of O. durum clearly bear dorsal gills. Ignoring O. durum because it was created for slugs with a smooth notum would have led to an incomplete list of available Peronia species names. Several species names had to be transferred to Peronia, because they refer to slugs with dorsal gills, regardless of whether species were originally described with dorsal gills or not. When type specimens are not located, one needs to go through original species descriptions very carefully, and still beyond the taxon of interest. Reciprocally, not all species names ever classified in Peronia belong to Peronia: for instance, several specific names originally combined with Peronia refer to Onchidella species. Finally, many species names of doubtful application need to be commented upon.

In total, 51 species-group names had to be considered for the revision of Peronia. Of these, only 31 are available Peronia species names (Table 1). Indeed, ten of those 51 names are not classified in Peronia: eight names refer to Onchidella species, one to a Wallaconchis species, and one to a Marmaronchis species. And, ten other names are nomina dubia as they refer to species which may belong to any onchidiid genus or which may not even belong to an onchidiid genus.

Table 1.

Alphabetic list of the 51 existing species-group names of which the nomenclatural status is addressed in the present work. Details can be found in the text: comments on the four valid Peronia species names, their synonyms, and the junior homonym are in the species remarks; comments on the fifteen nomina dubia and the ten names that must be classified in other genera are in the general discussion.

Species-group names Type locality Nomenclatural status
Peronia acinosa Gould, 1852 Fiji Nomen dubium (onchidiid or not)
Peronia alderi JE Gray, 1850 Unknown Nomen dubium (Peronia)
Peronia anomala Labbé, 1934a Red Sea New junior subjective synonym (P. verruculata, Red Sea)
Onchidium astridae Labbé, 1934b West Papua New junior subjective synonym (P. verruculata, unit #1)
Onchidium ater Lesson, 1831a West Papua Wallaconchis
Onchidium branchiferum Plate, 1893 Philippines New junior subjective synonym (P. verruculata, unit #1)
Scaphis carbonaria Labbé, 1934a New Caledonia New junior subjective synonym (P. verruculata, unit #1)
Onchidium celticum Cuvier in Audouin and Milne-Edwards 1832 France Onchidella
Onchidium cinereum Quoy & Gaimard, 1833 Tonga Nomen dubium (Wallaconchis)
Peronia corpulenta Gould, 1852 Fiji Nomen dubium (onchidiid or not)
Onchidium durum Labbé, 1934a Red Sea New junior subjective synonym (P. verruculata, Red Sea)
Onchidium elberti Simroth, 1920 Sulawesi Junior subjective synonym (P. verruculata, unit #1)
Onchidium ferrugineum Lesson, 1831a West Papua Junior subjective synonym (P. verruculata, unit #1)
Paraperonia fidjiensis Labbé, 1934a Fiji New junior subjective synonym (P. peronii)
Onchis fruticosa Stimpson, 1855 Japan Nomen dubium (Peronia)
Peronia gaimardi Labbé, 1934a Vanikoro New junior subjective synonym (P. verruculata, unit #1)
Paraperonia gondwanae Labbé, 1934a Western India New junior subjective synonym (P. verruculata, unit #4)
Paraperonia gondwanae hombroni Labbé, 1934a Torres Strait Nomen dubium (Peronia)
Onchidium granulosum Lesson, 1831b New Ireland Nomen dubium (onchidiid, Peronia or not)
Scaphis gravieri Labbé, 1934a Mayotte New junior subjective synonym (P. verruculata, unit #5)
Onchidella griseofusca Tapparone Canefri, 1874 Singapore Nomen dubium (onchidiid, Peronia or not)
Onchidium incisum Quoy & Gaimard, 1832 Ascension Island Onchidella
Quoya indica Labbé, 1934a Indian Ocean Nomen dubium (Peronia)
Peronia indolens Couthouy in Gould 1852 Brazil Onchidella
Peronia irrorata Gould, 1852 New Zealand Onchidella
Paraperonia jousseaumei Labbé, 1934a Red Sea New junior subjective synonym (P. madagascariensis)
Peronia laevis Blainville, 1826 West Papua Marmaronchis: junior objective synonym of Marmaronchis vaigiensis (Quoy & Gaimard, 1825)
Scaphis lata Labbé, 1934a Vietnam New junior subjective synonym (P. verruculata, unit #1)
Paraperonia madagascariensis Labbé, 1934a Madagascar Valid (Peronia madagascariensis)
Peronia mauritiana Blainville, 1824 Mauritius Junior objective synonym (P. peronii)
Peronia marginata Couthouy in Gould 1852 Tierra del Fuego Onchidella
Onchidium melanopneumon Bergh, 1884 Fiji Junior subjective synonym (P. peronii)
Onchidium multiradiatum Semper, 1882 Unknown Nomen dubium (onchidiid, Peronia or not)
Onchidium nebulosum Semper, 1880 Palau Nomen dubium (Peronia)
Onchidium nigricans Quoy & Gaimard, 1832 New Zealand Onchidella
Onchidium oniscoides Blainville, 1816 Unknown Nomen dubium (onchidiid, not Peronia)
Peronia parthenopeia Delle Chiaje, 1841 Sicily Onchidella
Onchidium patelloide Quoy & Gaimard, 1832 New Zealand Onchidella
Onchidium peronii Cuvier, 1804 Mauritius Valid (Peronia peronii)
Peronia persiae Maniei et al., 2020a Iran New junior subjective synonym (P. verruculata, unit #4)
Onchidium planatum Quoy & Gaimard, 1825 Guam Nomen dubium (onchidiid or not)
Onchidium platei Hoffmann, 1928 Tahiti Valid (Peronia platei)
Onchidium punctatum Quoy & Gaimard, 1832 West Papua New junior subjective synonym (P. peronii)
Peronia savignii Récluz, 1869 Red Sea New junior objective synonym (P. verruculata, Red Sea)
Onchidium savignyi Semper, 1880 Philippines Junior secondary homonym (P. savignii)
Peronia semituberculata Blainville, 1826 Guam Nomen dubium, junior objective synonym of Onchidium planatum Quoy & Gaimard, 1825 (nomen dubium)
Onchidium straelenii Labbé, 1934b Aru Islands Nomen dubium (onchidiid, not Peronia)
Onchidium tonganum Quoy & Gaimard, 1832 Tonga Junior subjective synonym (P. peronii)
Scaphis tonkinensis Labbé, 1934a Vietnam New junior subjective synonym (P. verruculata, unit #1)
Onchidium verruculatum Cuvier, 1830 Red Sea Valid (Peronia verruculata)
Scaphis viridis Labbé, 1934a Torres Strait New junior subjective synonym (P. verruculata, unit #1)

Incorrect subsequent spellings

Many subsequent incorrect spellings are encountered in the onchidiid literature. The subsequent incorrect spelling of a name is not available and, to our knowledge, no subsequent incorrect spelling is in prevailing usage (ICZN 1999: Article 33.3). Subsequent incorrect spellings of specific names are corrected throughout the present monograph. When a spelling mistake is quite big, it is pointed out, such as, for instance, when JE Gray (1850: 117) erroneously used Peronia tongensis instead of Peronia tongana, and when Mörch (1872b: 325) erroneously used Peronia vermiculata instead of Peronia verruculata. In addition, many Peronia species were originally classified in Buchannan’s (1800) Onchidium, for which some authors (e.g., Plate 1893; Hoffmann 1928; Labbé, 1934a) used the unjustified emendation Oncidium, which is systematically corrected as Onchidium.

Museum collection abbreviations

AM Australian Museum, Sydney, New South Wales, Australia

ANSP Academy of Natural Sciences, Drexel University, Philadelphia, Pennsylvania, USA

BNHS Bombay Natural History Society, Mumbai, India

BPBM Bernice Pauahi Bishop Museum, Honolulu, Hawaii, USA

CASIZ California Academy of Sciences, San Francisco, California, USA

ITBZC Institute of Tropical Biology, Zoology Collection, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam

MNHN Muséum national d’Histoire naturelle, Paris, France

MTQ Museum of Tropical Queensland, Townsville, Queensland, Australia

NHMD Zoological Museum, Natural History Museum of Denmark, University of Copenhagen, Denmark

NHMUK Natural History Museum, London, United Kingdom

NMSA KwaZulu-Natal Museum, Pietermaritzburg, KwaZulu-Natal, South Africa

NSMT National Museum of Nature and Science, Tokyo, Japan

NTM Museum and Art Gallery Northern Territory, Darwin, Northern Territory, Australia

PNM National Museum of the Philippines, Manila, Philippines

RBINS Royal Belgian Institute of Natural Sciences, Brussels, Belgium

SMF Senckenberg Forschungsinstitut und Naturmuseum, Frankfurt am Main, Germany

SMNH Swedish Museum of Natural History, Stockholm, Sweden

UF University of Florida, Gainesville, USA

UMIZ Universitas Malikussaleh, North Aceh, Sumatra, Indonesia

USMMC Universiti Sains Malaysia, Mollusk Collection, Penang, Malaysia

WAM Western Australian Museum, Perth, Western Australia, Australia

ZMB Museum für Naturkunde, Berlin, Germany

ZMH Zoologisches Museum, Hamburg, Germany

ZSM Zoologische Staatssammlung München, Munich, Germany

ZRC Zoological Reference Collection, Lee Kong Chian Natural History Museum, National University of Singapore

Collecting

Our molecular analyses and anatomical species descriptions are based on a data set of 179 individuals specifically gathered for the present study. Of those 179 individuals, 112 were collected by the Dayrat lab, of which 91 were deposited in countries or states of origin (Australia, Hawaii, India, Indonesia, Japan, Malaysia, Philippines, Singapore, Vietnam) and 21 (from Madagascar and Mauritius) were deposited at the MNHN. Of those 179 individuals, 36 were collected during MNHN expeditions organized by Philippe Bouchet (Madagascar, Mozambique, New Caledonia, Papua New Guinea, and Vanuatu) and are all preserved at the MNHN; the specimens from New Caledonia were collected by Adam Bourke. Of those 179 individuals, 12 were collected by several collaborators: Sadar Aslam collected three specimens from Pakistan deposited at the MNHN; Clay Carlson collected two specimens from Guam deposited at the CAS and the MNHN; Owen Griffiths collected one specimen from Mauritius deposited at the MNHN; Shau Hwai (Aileen) Tan collected two specimens from Malaysia deposited at the USM; and Tomoyuki Nakano collected four specimens from Japan deposited at the NSMT. And, finally, 19 were found in museum collections: four (AM), four (NHMUK), two (NMSA), and nine (UF).

Collecting expeditions of the Dayrat lab were led by Benoît Dayrat in the Andaman Islands (India), West Bengal (India), Peninsular Malaysia, the Philippines, Singapore, New South Wales (Australia), and Northern territory (Australia), by Tricia Goulding in Queensland (Australia), Mauritius, Madagascar, Vietnam, and western India, by Munawar Khalil in Indonesia, and by Rebecca Cumming in Japan. Sites were accessed by car or by boat. Although each site was explored for an average of two hours, the exact time spent at each site also depended on the time of the low tide, the weather conditions, etc. Photographs were taken to document the kind of habitat being visited as well as the diverse microhabitats where specimens were collected. Specimens were individually numbered and photographed in their respective habitat. At each site, as much diversity as possible was sampled: even specimens that looked similar were individually numbered so that the presence of cryptic diversity could be tested. Importantly, a piece of tissue was cut for all specimens individually numbered for DNA extraction and the remainder of each specimen was relaxed (using magnesium chloride) and fixed (using 10% formalin or 70% ethanol) for comparative anatomy.

Specimens

Specimens included in molecular analyses. DNA extraction numbers unique to each individual are indicated in phylogenetic trees as well as in lists of material examined and in figure captions (numbers are between brackets). Our molecular data set includes 190 Peronia individuals, only eleven of which correspond to COI sequences obtained from GenBank or BOLD (Table 2). Anatomical descriptions are based on those 179 Peronia individuals for which sequences were generated for the present study as well as the available type material for existing names (see below).

All DNA sequences for the eleven outgroups are from our previous studies (Dayrat et al. 2016, 2017, 2018, 2019a, b, c, d; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c), with the exception of the nuclear sequences for Laspionchis boucheti, which are new (Table 2). Most Peronia mitochondrial and nuclear sequences in our molecular data set are new (Table 2). New mitochondrial COI and 16S sequences are provided for 169 individuals, and COI and 16S sequences for ten specimens are from a previous study (Dayrat et al. 2011; see below). In addition, all COI sequences in GenBank and BOLD closely related to Peronia sequences in our dataset were examined, and COI sequences for eleven individuals were selected to be included in phylogenetic analyses (Table 2; see below). All nuclear 28S and ITS2 sequences are new except for two individuals which have been used as outgroups in several of our previous studies: [696-2] from Okinawa and [706] from Hawaii (Table 2).

Table 2.

DNA extraction numbers and GenBank accession numbers for all the specimens included in the present study. The letter H next to an extraction number indicates the holotype. Sequences marked with an asterisk (*) are from our former publications (Dayrat et al. 2011, 2016, 2017, 2018, 2019a, b, c, d; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c). In addition, 11 COI sequences also marked with an asterisk (*) were obtained from GenBank (GB) and BOLD: four sequences from China (Sun et al. 2014), two from Singapore (Chang et al. 2018), two from Japan (Takagi et al. 2019), one from the Persian Gulf (unpublished), one from Gujarat, western India (unpublished), and one from Iran (Maniei et al. 2020a). Abbreviations: Australian Museum, Sydney (AM); Bombay Natural History Society, India (BNHS); Bernice Pauahi Bishop Museum, Honolulu, Hawaii, USA (BPBM); California Academy of Sciences, San Francisco, California, USA (CASIZ); Institute of Tropical Biology, Zoology Collection, Vietnam Academy of Science and Technology (ITBZC); Muséum national d’Histoire naturelle, Paris, France (MNHN); Museum of Tropical Queensland, Townsville, Queensland, Australia (MTQ); Natural History Museum, London, United Kingdom (NHMUK); KwaZulu-Natal Museum, Pietermaritzburg, KwaZulu-Natal, South Africa (NMSA); National Museum of Nature and Science, Tokyo, Japan (NSMT); Museum and Art Gallery Northern Territory, Darwin, Northern Territory, Australia (NTM); National Museum of the Philippines, Manila (PNM); University of Florida, Gainesville, Florida, USA (UF); Universitas Malikussaleh, North Aceh, Sumatra, Indonesia (UMIZ); Universiti Sains Malaysia Mollusc Collection, Penang, Malaysia (USMMC); Zoological Reference Collection, Lee Kong Chian Natural History Museum, National University of Singapore (ZRC).

Species Individual (DNA #) Voucher Locality GenBank COI GenBank 16S GenBank ITS2 GenBank 28S
Alionchis jailoloensis 5137 H UMIZ 00117 Indonesia, Halmahera MG953528* MG953538* MG953548* MK122918*
Laspionchis boucheti 1688 H NTM P.57614 Australia, Northern Territory MH619249* MH619310* MT652862 MT652995
Marmaronchis vaigiensis 1183 ZRC.MOL.3007 Singapore MK122812* MK122854* MK122877* MK122910*
Melayonchis eloisae 1011 H ZRC.MOL.6499 Singapore KX240026* KX240050* MK122904* MK125515*
Onchidella celtica 5013 MNHN-IM-2019-1604 France MG958715* MG958717* MK122906* MK122921*
Onchidina australis 1523 AM C.468918.002 Australia, New South Wales KX179548* KX179561* MG958719* MG958887*
Onchidium typhae 965 USMMC 00005 Peninsular Malaysia KX179509* KX179525* MG958720* MG958885*
Paromoionchis tumidus 1732 UMIZ 00121 Indonesia, Sumatra MH054951* MH055104* MH055196* MH055268*
Peronina tenera 960 USMMC 00039 Peninsular Malaysia MG958740* MG958796* MG958840* MG958874*
Platevindex luteus 1001 ZRC.MOL.10179 Singapore MG958714* MG958716* MG958718* MG958888*
Wallaconchis sinanui 2740 UMIZ 00059 Indonesia, Ambon MG970713* MG970881* MG971093* MG971161*
P. verruculata (unit #1) 1538 AM C.448363 Australia, Queensland (19°S) MT653148 MT652693 MT652863 MT652996
2571 MTQ Australia, Queensland (16°S) MT653149 MT652694 MT652864
2620 MTQ Australia, Queensland (20°S) MT653150 MT652695
2622 MTQ Australia, Queensland (20°S) MT653151 MT652696
2682 MTQ Australia, Queensland (21°S) MT653152 MT652697 MT652865
GB China, Guangdong (21°N) JN543152*
GB China, Fujian (26°N) JN543153*
GB China, Guangxi (21°N) JN543154*
GB China, Hainan (18°N) JN543165*
2724 UMIZ 00162 Indonesia, Ambon (03°S) MT653153 MT652698 MT652866 MT652997
P. verruculata (unit #1) 2729 UMIZ 00162 Indonesia, Ambon (03°S) MT653154 MT652699
2856 UMIZ 00163 Indonesia, Ambon (03°S) MT653155 MT652700 MT652867
3080 UMIZ 00164 Indonesia, Bali (08°S) MT653156 MT652701 MT652868
3115 UMIZ 00165 Indonesia, Bali (08°S) MT653157 MT652702 MT652869
5068 UMIZ 00166 Indonesia, Halmahera (00°S) MT653158 MT652703
5120 UMIZ 00167 Indonesia, Halmahera (01°S) MT653159 MT652704 MT652870
5124 UMIZ 00167 Indonesia, Halmahera (01°S) MT653160 MT652705
5130 UMIZ 00167 Indonesia, Halmahera (01°S) MT653161 MT652706
2987 UMIZ 00168 Indonesia, Lombok (08°S) MT653162 MT652707 MT652871
2868 UMIZ 00169 Indonesia, Seram (02°S) MT653163 MT652708
2870 UMIZ 00169 Indonesia, Seram (02°S) MT653164 MT652709 MT652872 MT652998
3441 UMIZ 00169 Indonesia, Seram (02°S) MT653165 MT652710
731 NHMUK 20050628 Indonesia, Sulawesi HQ660046* HQ659914*
2127 UMIZ 00170 Indonesia, Sulawesi (01°N) MT653166 MT652711
2150 UMIZ 00171 Indonesia, Sulawesi (01°N) MT653167 MT652712
2162 UMIZ 00171 Indonesia, Sulawesi (01°N) MT653168 MT652713 MT652873
1747 UMIZ 00172 Indonesia, Sumatra (05°S) MT653169 MT652714 MT652874
1759 UMIZ 00173 Indonesia, Sumatra (05°S) MT653170 MT652715 MT652875 MT652999
5904 UMIZ 00174 Indonesia, Timor (10°S) MT653171 MT652716 MT652876
5925 UMIZ 00175 Indonesia, Timor (10°S) MT653172 MT652717 MT652877
5927 UMIZ 00175 Indonesia, Timor (10°S) MT653173 MT652718
3751 NSMT-Mo 78988 Japan, Wakayama (33°N) MT653174 MT652719 MT652878
3752 NSMT-Mo 78988 Japan, Wakayama (33°N) MT653175 MT652720 MT652879 MT653000
GB Japan, Kagoshima (31°N) LC390389*
6202 MNHN-IM-2019-1591 New Caledonia (22°S) MT653176 MT652721 MT652880 MT653001
6212 MNHN-IM-2019-1592 New Caledonia (22°S) MT653177 MT652722 MT652881 MT653002
6214 MNHN-IM-2019-1593 New Caledonia (21°S) MT653178 MT652723 MT652882
698 UF 253871 Palau (07°N) MT653179 MT652724 MT652883 MT653003
5467 MNHN-IM-2013-12008 PNG, Madang (05°S) MT653180 MT652725
5468 MNHN-IM-2013-12009 PNG, Madang (05°S) MT653181 MT652726 MT652884 MT653004
5469 MNHN-IM-2013-12010 PNG, Madang (05°S) MT653182 MT652727
6085 MNHN-IM-2013-50974 PNG, New Ireland (02°S) MT653183 MT652728 MT652885 MT653005
6087 MNHN-IM-2013-53523 PNG, New Ireland (02°S) MT653184 MT652729
P. verruculata (unit #1) 6088 MNHN-IM-2013-53525 PNG, New Ireland (02°S) MT653185 MT652730
3379 PNM 041274 Philippines, Bohol (09°N) MT653186 MT652731
3380 PNM 041274 Philippines, Bohol (09°N) MT653187 MT652732 MT652886
3433 PNM 041276 Philippines, Bohol (09°N) MT653188 MT652733
3437 PNM 041276 Philippines, Bohol (09°N) MT653189 MT652734
712 UF 368518 Philippines, Cebu (09°N) HQ660050* HQ65991*
3160 PNM 041277 Philippines, Luzon (13°N) MT653190 MT652735 MT652887
3161 PNM 041277 Philippines, Luzon (13°N) MT653191 MT652736
704 UF 368517 Philippines, Negros (09°N) MT653192 MT652737
991 ZRC.MOL.10497 Singapore (01°N) MT653193 MT652738 MT652888 MT653006
GB Singapore MH002570*
5480 MNHN-IM-2013-62392 Vanuatu (17°S) MT653194 MT652739 MT652889
5481 MNHN-IM-2013-62393 Vanuatu (17°S) MT653195 MT652740 MT652890 MT653007
5620 ITBZC IM 00021 Vietnam (12°N) MT653196 MT652741 MT652891
5621 ITBZC IM 00021 Vietnam (12°N) MT653197 MT652742
5639 ITBZC IM 00023 Vietnam (08°N) MT653198 MT652743 MT652892
5670 ITBZC IM 00022 Vietnam (08°N) MT653199 MT652744 MT652893
P. verruculata (unit #2) 1072 BNHS 1072 India, Andaman (11°N) MT653200 MT652745
1077 BNHS 119 India, Andaman (11°N) MT653201 MT652746
1079 BNHS 120 India, Andaman (11°N) MT653202 MT652747
1080 BNHS 121 India, Andaman (11°N) MT653203 MT652748
1081 BNHS 122 India, Andaman (11°N) MT653204 MT652749
1084 BNHS 117 India, Andaman (11°N) MT653205 MT652750
1741 UMIZ 00179 Indonesia, Sumatra (05°S) MT653206 MT652751 MT652894
1742 UMIZ 00179 Indonesia, Sumatra (05°S) MT653207 MT652752 MT652895
1746 UMIZ 00178 Indonesia, Sumatra (05°S) MT653208 MT652753 MT652896 MT653008
1795 UMIZ 00180 Indonesia, Sumatra (05°S) MT653209 MT652754 MT652897
1796 UMIZ 00180 Indonesia, Sumatra (05°S) MT653210 MT652755 MT652898
1797 UMIZ 00180 Indonesia, Sumatra (05°S) MT653211 MT652756 MT652899 MT653009
P. verruculata (unit #3) 974 USMMC 00064 Peninsular Malaysia (06°N) MT653212 MT652757 MT652900 MT653010
975 USMMC 00064 Peninsular Malaysia (06°N) MT653213 MT652758 MT652901
976 USMMC 00051 Peninsular Malaysia (06°N) MT653214 MT652759 MT652902
977 USMMC 00064 Peninsular Malaysia (06°N) MT653215 MT652760 MT652903
2546 USMMC 00065 Peninsular Malaysia (05°N) MT653216 MT652761 MT652904 MT653011
2547 USMMC 00065 Peninsular Malaysia (05°N) MT653217 MT652762 MT652905 MT653012
989 ZRC.MOL.16070 Singapore (01°N) MT653218 MT652763 MT652906 MT653013
P. verruculata (unit #3) 990 ZRC.MOL.10496 Singapore (01°N) MT653219 MT652764 MT652907 MT653014
GB Singapore MH002601*
P. verruculata (unit #4) 1141 BNHS 22 India, western coast (19°N) MT653220 MT652765
1143 BNHS 24 India, western coast (19°N) MT653221 MT652766
1144 BNHS 23 India, western coast (19°N) MT653222 MT652767
6164 MNHN-IM-2019-1384 Pakistan (24°N) MT653223 MT652768 MT652908 MT653015
6165 MNHN-IM-2019-1385 Pakistan (24°N) MT653224 MT652769 MT652909 MT653016
6166 MNHN-IM-2019-1386 Pakistan (24°N) MT653225 MT652770 MT652910 MT653017
GB Iran (26°N) MK993404* MK993392*
P. verruculata (unit #5) 3140 MNHN-IM-2019-1610 Madagascar (12°S) MT653226 MT652771 MT652911 MT653018
3142 MNHN-IM-2019-1610 Madagascar (12°S) MT653227 MT652772 MT652912
3143 MNHN-IM-2019-1611 Madagascar (12°S) MT653228 MT652773 MT652913
3144 MNHN-IM-2019-1611 Madagascar (12°S) MT653229 MT652774 MT652914
3146 MNHN-IM-2019-1611 Madagascar (12°S) MT653230 MT652775 MT652915 MT653019
3149 MNHN-IM-2019-1611 Madagascar (12°S) MT653231 MT652776 MT652916
3231 MNHN-IM-2019-1610 Madagascar (12°S) MT653232 MT652777 MT652917
3597 MNHN-IM-2019-1610 Madagascar (12°S) MT653233 MT652778 MT652918
3598 MNHN-IM-2019-1610 Madagascar (12°S) MT653234 MT652779 MT652919
3600 MNHN-IM-2019-1611 Madagascar (12°S) MT653235 MT652780 MT652920 MT653020
730 NHMUK 20080190 Mozambique (12°S) HQ660045* HQ659913*
733 NHMUK 20060257 Mozambique (11°S) HQ660047* HQ659915*
5507 MNHN-IM-2013-62395 Mozambique (26°S) MT653236 MT652781 MT652920 MT653021
5510 MNHN-IM-2013-62398 Mozambique (26°S) MT653237 MT652782 MT652920 MT653022
P. griffithsi 2934 UMIZ 00177 Indonesia, Kei (05°S) MT653238 MT652783 MT652923 MT653023
2936 UMIZ 00176 Indonesia, Kei (05°S) MT653239 MT652784 MT652924 MT653024
3566 UMIZ 00177 Indonesia, Kei (05°S) MT653240 MT652785 MT652925
3153 MNHN-IM-2019-1608 Mauritius (20°S) MT653241 MT652786 MT652926 MT653025
3154 MNHN-IM-2019-1608 Mauritius (20°S) MT653242 MT652787 MT652927 MT653026
3155 MNHN-IM-2019-1608 Mauritius (20°S) MT653243 MT652788
3156 MNHN-IM-2019-1608 Mauritius (20°S) MT653244 MT652789 MT652928 MT653027
3157 H MNHN-IM-2000-35265 Mauritius (20°S) MT653245 MT652790 MT652929 MT653028
3606 MNHN-IM-2019-1608 Mauritius (20°S) MT653246 MT652791 MT652930
3607 MNHN-IM-2019-1608 Mauritius (20°S) MT653247 MT652792
3608 MNHN-IM-2019-1608 Mauritius (20°S) MT653248 MT652793 MT652931
6095 MNHN-IM-2013-53535 PNG, New Ireland (02°S) MT653249 MT652794 MT652932 MT653029
P. madagascariensis BOLD India, Gujarat, Dwarka (22°N) LGEN099-14*
GB Iran, Persian Gulf LC027608*
5500 MNHN-IM-2009-16391 Madagascar (25°S) MT653250 MT652795 MT652933
5501 MNHN-IM-2009-16392 Madagascar (25°S) MT653251 MT652796 MT652934 MT653030
5502 MNHN-IM-2009-16393 Madagascar (25°S) MT653252 MT652797 MT652935
5503 MNHN-IM-2009-16396 Madagascar (25°S) MT653253 MT652798 MT652936
5504 MNHN-IM-2009-16412 Madagascar (25°S) MT653254 MT652799
5506 MNHN-IM-2009-16418 Madagascar (25°S) MT653255 MT652800 MT652937 MT653031
735 NHMUK 20060414 Mozambique (12°S) HQ660042* HQ659910* MT652938 MT653032
703 UF 332088 Oman (23°N) MT653256 HQ659912* MT652939 MT653033
5841 NMSA W7547 South Africa (29°S) MT653257 MT652801 MT652940 MT653034
5842 NMSA W7547 South Africa (29°S) MT653258 MT652802 MT652941 MT653035
P. okinawensis 696-2 UF 352288 Japan, Okinawa (26°N) HQ660043* HQ659911* MG958871* MG958883*
696-3 UF 352288 Japan, Okinawa (26°N) MT653259 MT652803 MT652942 MT653036
696-4 H UF 352288 Japan, Okinawa (26°N) MT653260 MT652804 MT652943 MT653037
P. peronii 443 CASIZ 180486 Guam (13°N) HQ660041* HQ659909* MT652944 MT653038
5840 MNHN-IM-2019-1609 Guam (13°N) MT653261 MT652805 MT652945 MT653039
GB Japan, Okinawa LC390402*
1553 MNHN-IM-2019-1607 Mauritius (20°S) MT653262 MT652806 MT652946 MT653040
3605 MNHN-IM-2019-1606 Mauritius (20°S) MT653263 MT652807 MT652947 MT653041
5872 MNHN-IM-2019-1605 Mauritius (20°S) MT653264 MT652808 MT652948
5874 MNHN-IM-2019-1605 Mauritius (20°S) MT653265 MT652809 MT652949
5471 MNHN-IM-2013-12500 PNG, Madang (05°S) MT653266 MT652810 MT652950 MT653042
5472 MNHN-IM-2013-14052 PNG, Madang (05°S) MT653267 MT652811 MT652951 MT653043
5474 MNHN-IM-2013-14054 PNG, Madang (05°S) MT653268 MT652812 MT652952
5476 MNHN-IM-2013-16260 PNG, Madang (05°S) MT653269 MT652813 MT652953 MT653044
5477 MNHN-IM-2013-15872 PNG, Madang (05°S) MT653270 MT652814 MT652954 MT653045
6086 MNHN-IM-2013-53482 PNG, New Ireland (02°S) MT653271 MT652815 MT652955 MT653046
P. platei 5405 MNHN-IM-2013-13762 PNG, Madang (05°S) MT653272 MT652816
5410 MNHN-IM-2013-15765 PNG, Madang (05°S) MT653273 MT652817 MT652956
5412 MNHN-IM-2013-13351 PNG, Madang (05°S) MT653274 MT652818 MT652957 MT653047
5464 MNHN-IM-2013-15871 PNG, Madang (05°S) MT653275 MT652819 MT652958 MT653048
706 UF 303653 USA, Hawaii (21°N) HQ660038* HQ659906* MG958722* MG958884*
5380 UF 303653 USA, Hawaii (21°N) MT653276 MT652820 MT652959 MT653049
6160 BPBM 284527 USA, Hawaii (21°N) MT653277 MT652821 MT652960 MT653050
6161 BPBM 284528 USA, Hawaii (21°N) MT653278 MT652822 MT652961 MT653051
P. setoensis 3753 NSMT-Mo 78987 Japan, Wakayama (33°N) MT653279 MT652823 MT652962 MT653052
3754 NSMT-Mo 78987 Japan, Wakayama (33°N) MT653280 MT652824 MT652963 MT653053
5382 NSMT-Mo 78986 Japan, Wakayama (33°N) MT653281 MT652825 MT652964 MT653054
5383 H NSMT-Mo 78985 Japan, Wakayama (33°N) MT653282 MT652826 MT652965 MT653055
5384 NSMT-Mo 78986 Japan, Wakayama (33°N) MT653283 MT652827 MT652966 MT653056
5385 NSMT-Mo 78986 Japan, Wakayama (33°N) MT653284 MT652828 MT652967
P. sydneyensis 1513 AM C.468912.004 New South Wales (33°S) MT653285 MT652829 MT652968 MT653057
1516 H AM C.468916.001 New South Wales (33°S) MT653286 MT652830 MT652969 MT653058
1517 AM C.468915.001 New South Wales (33°S) MT653287 MT652831 MT652970 MT653059
734 AM C.459511 Queensland (22°S) HQ660048* HQ659916*
1539 AM C.459510 Queensland (22°S) MT653288 MT652832
1540 AM C.459511 Queensland (22°S) MT653289 MT652833 MT652971 MT653060
2646 MTQ Queensland (20°S) MT653290 MT652834 MT652972
2653 MTQ Queensland (20°S) MT653291 MT652835 MT652973
2656 MTQ Queensland (20°S) MT653292 MT652836 MT652974
2661 MTQ Queensland (20°S) MT653293 MT652837
2662 MTQ Queensland (20°S) MT653294 MT652838 MT652975 MT653061
2664 MTQ Queensland (20°S) MT653295 MT652839 MT652976
P. sydneyensis 2667 MTQ Queensland (20°S) MT653296 MT652840
2680 MTQ Queensland (21°S) MT653297 MT652841
6189 MNHN-IM-2019-1594 New Caledonia (22°S) MT653298 MT652842 MT652977
6195 MNHN-IM-2019-1595 New Caledonia (22°S) MT653299 MT652843 MT652978 MT653062
6209 MNHN-IM-2019-1596 New Caledonia (22°S) MT653300 MT652844 MT652979
6213 MNHN-IM-2019-1597 New Caledonia (21°S) MT653301 MT652845 MT652980 MT653063
6220 MNHN-IM-2019-1598 New Caledonia (21°S) MT653302 MT652846 MT652981 MT653064
6222 MNHN-IM-2019-1599 New Caledonia (21°S) MT653303 MT652847 MT652982
P. willani 1620 NTM P.57626 Northern Territory (12°S) MT653304 MT652848 MT652983 MT653065
1623 NTM P.57627 Northern Territory (12°S) MT653305 MT652849 MT652984 MT653066
1624 NTM P.57627 Northern Territory (12°S) MT653306 MT652850 MT652985
1625 NTM P.57627 Northern Territory (12°S) MT653307 MT652851 MT652986
1626 NTM P.57627 Northern Territory (12°S) MT653308 MT652852 MT652987 MT653067
1628 H NTM P.57625 Northern Territory (12°S) MT653309 MT652853 MT652988 MT653068
1629 NTM P.57627 Northern Territory (12°S) MT653310 MT652854
1653 NTM P.57626 Northern Territory (12°S) MT653311 MT652855 MT652989
1654 NTM P.57626 Northern Territory (12°S) MT653312 MT652856 MT652990
1655 NTM P.57626 Northern Territory (12°S) MT653313 MT652857 MT652991 MT653069
1667 NTM P.57627 Northern Territory (12°S) MT653314 MT652858 MT652992 MT653070
1668 NTM P.57627 Northern Territory (12°S) MT653315 MT652859 MT652993
1669 NTM P.57627 Northern Territory (12°S) MT653316 MT652860
1670 NTM P.57627 Northern Territory (12°S) MT653317 MT652861

COI sequences publicly available. Eleven COI sequences obtained from GenBank (10) and BOLD (1) were added to our own data set (179 COI sequences) for a total of 190 sequences. Four COI sequences are from China (Sun et al. 2014), two from Singapore (Chang et al. 2018), two from Japan (Takagi et al. 2019), one from the Persian Gulf (unpublished), one from Gujarat, western India (unpublished), and one from Iran (Maniei et al. 2020a). All those sequences were merely referred to as Peronia sp., except for the specimens from China (referred to as Peronia verruculata), the specimen from western India (referred to as Onchidium verruculatum), and the specimen from Iran (recently described as P. persiae, a name regarded here as a synonym of P. verruculata, unit #4). Correct identifications are provided here for all those sequences (Table 2). Note that in the case of duplicate sequences available in GenBank, only one representative was selected. So, for instance, Chang et al. (2018) published many Peronia COI sequences that cluster in two mitochondrial units which they refer to as “Singapore clade” and “Peronia sp. 2 clade.” One sequence for their “Singapore clade” and one sequence for their “Peronia sp. 2 clade” are included here, which is enough to demonstrate that their two units correspond to our two mitochondrial units #1 and #3 of Peronia verruculata. Also, all COI sequences by Maniei et al. (2020a) for P. persiae cluster together within the unit #4 of P. verruculata, so only one of those individuals is included in our analyses: one individual is enough to demonstrate that P. persiae is a junior synonym of P. verruculata. A 16S sequence is available for the individual from Iran (Maniei et al. 2020a); no 16S sequences are available for any of the other COI sequences from GenBank and BOLD, so gaps were inserted in the mitochondrial concatenated alignment.

Vouchers used in Dayrat et al. (2011). Ten of our Peronia specimens were tentatively identified by Dayrat et al. (2011) at a time when nothing was known about the onchidiid species diversity in general and most especially in the genus Peronia. Most of those ten specimens were merely referred to with numbers (e.g., Peronia sp. 1). In order to avoid any confusion, those specimens are all included here so that correct species names are provided (Table 2). The specimen [443] (CASIZ 180486) identified as Peronia peronii from Guam really belongs to P. peronii. The specimen [696-2] (UF 352288) identified as Peronia cf. verruculata from Okinawa belongs to the new species P. okinawensis. The specimen [706] (UF 303653) identified as Peronia sp. 1 from Hawaii belongs to P. platei. The specimen [734] (AM C.459511) identified as Peronia sp. 3 from Queensland, Australia, belongs to the new species P. sydneyensis. Two specimens belong to P. madagascariensis: [735] (NHMUK 20060414) identified as Peronia cf. peronii from Mozambique, and [703] (UF 332088) identified as Peronia sp. 2 from Oman. Four specimens belong to P. verruculata: [712] (UF 368518) identified as Scaphis sp. from Cebu, Philippines, [730] (NHMUK 20080190) identified as Peronia sp. 4 from Mozambique, [733] (NHMUK 20060257) identified as Peronia sp. 5 from Mozambique, and [731] (NHMUK 20050628) identified as Peronia sp. 6 from Sulawesi, Indonesia.

Types of existing species-group names. All type specimens available for all onchidiid species-group names have been examined in context of the revision of the entire family. Comments on many onchidiid types can be found in our previous revisions (Dayrat et al. 2016, 2017, 2018, 2019a, b, c, d; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c). In total, 118 type specimens (holotypes, lectotypes, paralectotypes, syntypes, etc.) are commented on here for the first time. Fifteen of those 118 type specimens are commented on in the general discussion because they are types of nomina dubia which may or may not refer to Peronia slugs. All the other (103) types are commented on in species descriptions because they are the types of 25 species-group names which must be classified in Peronia and which are not nomina dubia (Table 1).There are only two Peronia species names for which types could not be located: Scaphis lata Labbé, 1934a, and Paraperonia jousseaumei Labbé, 1934a. Finally, 14 lectotypes are designated here in order to clarify the application of 14 species names, usually because syntypes belong to different species or come from very distant localities.

Many type specimens were not labeled as types and were found within the general collections. In most cases, it was easy to determine that specimens were types because the information on the labels would match perfectly to that of the original descriptions. However, finding Labbé’s types was challenging, with the exception of the holotype, by monotypy, of Onchidium astridae Labbé, 1934b, preserved in Bruxelles (RBINS I.G.9223/MT.3822): it was not marked as a holotype, but the name Onchidium astridae is on the label, and the locality and collector information is matching.

The types of all the other Peronia species (and one subspecies) described by Labbé are preserved at the MNHN (the monograph in which those new taxa were described was almost exclusively based on material from the MNHN). The major issue with this material is that Labbé did not write any of his new species names on any of the labels. To be fair and fully accurate, there are actually three jars for which a specific name was written in pencil and in tiny letters on labels: one jar contains the type material of Onchidium durum (MNHN-IM-2000-33698), and two other jars contain part of the type material of Paraperonia gondwanae (MNHN-IM-2000-33683, MNHN-IM-2000-33688). Eleven years ago, Dayrat (2009) considered that identifying the types of Labbé’s onchidiid species names in the MNHN collection would be too risky (because specimens could be erroneously interpreted as types). However, after Virginie Héros (who is in charge of the Mollusk type collection at the MNHN) correctly remarked that it should still be possible to find some of Labbé’s types, an excel file was generated including all the old onchidiid material preserved at the MNHN and all the material cited in Labbé’s (1934a) monograph. By comparing various information (localities, names of the collectors, collecting dates, specimen sizes), it then became clear that many specimens could be identified as types with great confidence, even though they were not labeled as types and Labbé’s species names were not indicated on the labels.

For instance, originally, no jar clearly labeled as the type material of Scaphis carbonaria was found at the MNHN. However, of the old jars found at the MNHN with specimens from New Caledonia, only one matches perfectly the information provided in Labbé’s original description of S. carbonaria: an individual collected in 1880 by Réveillère (with an identification as Peronia). Other jars with one or more specimens from New Caledonia were collected by Fisher in 1878 and by François in 1894. Therefore, it is extremely likely that the specimen collected by Réveillère in 1880 is the holotype, by monotypy, of Scaphis carbonaria (MNHN-IM-2000-33708). In many cases, however, identifying the types happened to be much more challenging because there were several jars with the same locality, the same collector, and the same collecting date. In order to avoid any future confusion, Labbé’s types are commented on in great detail in species descriptions. There are only two of Labbé’s species for which no type material could be confidently traced back at the MNHN: Scaphis lata Labbé, 1934a, and Paraperonia jousseaumei Labbé, 1934a.

Finally, the type material of Peronia persiae, recently described by Maniei et al. (2020a), was not borrowed for examination. Regardless, there is no doubt that P. persiae is a junior synonym of both P. verruculata (Cuvier, 1830) and P. gondwanae (Labbé, 1934a) (Table 1), because all the COI and 16S sequences published for P. persiae cluster within the mitochondrial unit #4 of P. verruculata.

Additional material examined (historical museum collections). In addition to the 189 specimens included in the molecular analyses (not including the eleven outgroups) and the 118 type specimens of existing nominal species, 297 old specimens were obtained from museum collections from which no DNA could be extracted. Those specimens correspond to a total of 60 jars. One jar contains 161 specimens. All other jars contain fewer than 15 specimens. These old museum specimens are not included in the anatomical species descriptions, except for the description of Peronia verruculata from the Red Sea. Instead, these additional specimens are commented on in the species remarks. The additional specimens were especially useful to provide geographic records from places which could not be visited, such as the Chagos Archipelago, Nicobar Islands, Persian Gulf, and Socotra. Identifying Peronia species using only anatomical traits is challenging but possible (see below). Finally, some of the historical specimens from museum collections were studied by previous authors, and their re-examination allowed us to confirm or reject many identifications from the literature.

Anatomical preparations and descriptions

Size (length/width) is indicated in millimeters (mm) for each specimen. Both the external morphology and the internal anatomy were studied. All anatomical observations were made under a dissecting microscope and drawn with a camera lucida. Radulae and male reproductive organs were prepared for scanning electron microscopy (Zeiss SIGMA Field Emission Scanning Electron Microscopy). Radulae were cleaned in 10% NaOH for a week, rinsed in distilled water, briefly cleaned in an ultrasonic water bath (less than a minute), sputter-coated with gold-palladium and examined by SEM. Soft parts (penis, accessory penial gland, etc.) were dehydrated in ethanol and critical point dried before coating.

Anatomical species descriptions are based on those 179 Peronia individuals for which sequences were generated for the present study as well as on the available type material for species with existing names (see below). To avoid unnecessary repetition, the description of anatomical features that are virtually identical between Peronia species (e.g., nervous system, heart, and stomach) is not repeated for each species. However, all the characters that are useful for species comparison (e.g., intestinal loops and male apparatus) are described for every species. Special attention has been given to illustrating the holotype and the type locality of each new species.

Species are being described following a phylogenetic order. The detailed description of Peronia verruculata is based on the mitochondrial unit #1, by far the most widespread (from Peninsular Malaysia to the West Pacific) and most abundant (55 specimens in our study), but variations in the other units are precisely reported and figure captions indicate the unit to which each illustrated individual belongs.

Types of intestinal loops

In onchidiids, types of intestinal loops are defined based on the pattern of the intestine on the dorsal aspect of the digestive gland (with the digestive gland still in place). Plate (1893) first distinguished four types of intestinal loops (types I to IV) and Labbé (1934a) later added a type V. Only the types I and V are found in Peronia. Hoffmann (1928: 51, pl. 3, fig. 11) noted before Labbé that intestinal loops of type V differ from other types and he referred to them as type Ia. Labbé’s terminology (type V) is preferred because past authors have adopted it and because a type V is very different from a type I. The different types of intestinal loops and their individual variation are best revealed by coloring sections of the intestine differently (Dayrat et al. 2019b, c, d): a clockwise intestinal loop is colored in blue, a counterclockwise intestinal loop is colored in yellow, and a transitional loop between them is colored in green (Fig. 1).

The intestine first appears dorsally on the right side. In intestinal loops of type I, the intestine starts by forming a clockwise (blue) loop which does not make a complete circle. As a result, the transitional (green) loop is oriented to the right (Fig. 1A–F). In two species with intestinal loops of type I (P. okinawensis and P. peronii), the transitional loop is oriented between 12 and 3 o’clock (Fig. 1D–F). In the three other species with intestinal loops of type I (P. sydneyensis, P. verruculata, and P. willani), the transitional loop is oriented between 3 and 6 o’clock (Fig. 1A–C). In intestinal loops of type V, the intestine starts by forming immediately a counterclockwise (yellow) loop. In intestinal loops of type V, the counterclockwise loop is oriented between 10 and 11 o’clock (Fig. 1G–I). Four Peronia species are characterized by intestinal loops of type V: P. griffithsi, P. madagascariensis, P. platei, and P. setoensis.

Figure 1. 

Intestinal types found in Peronia species. A clockwise intestinal loop is colored in blue, a counterclockwise intestinal loop is colored in yellow, and a transitional loop between them is colored in green. The big red arrow indicates the orientation of the transitional loop (A–F) or counterclockwise loop (G–I), and the small black arrows indicates the direction of the intestinal transport A type I, with a transitional loop oriented at 3 o’clock, P. sydneyensis, Australia, New South Wales, [1517] (AM C.468915.001) B type I, with a transitional loop oriented at 6 o’clock, P. verruculata, lectotype of P. anomala, Red Sea (MNHN-IM-2000-33678) C type I, with a transitional loop oriented between 4 and 5 o’clock, P. verruculata, lectotype, Red Sea (MNHN-IM-2000-22941) D type I, with a transitional loop oriented at 3 o’clock, P. peronii, paralectotype of Onchidium peronii, Timor (MNHN-IM-2000- 22938) E type I, with a transitional loop oriented at 1 o’clock, P. peronii, lectotype of Paraperonia fidjiensis, Fiji (MNHN-IM-2000-33692) F type I, with a transitional loop oriented between 1 and 2 o’clock, P. okinawensis, holotype, Japan, Okinawa, [696-4 H] (UF 352288) G type V, with a counterclockwise loop oriented between 10 and 11 o’clock, P. madagascariensis, Madagascar, [5501] (MNHN-IM-2009-16392) H type V, with a counterclockwise loop oriented at 10 o’clock, P. platei, lectotype, French Polynesia (SMNH-Type-7537) I type V, with a counterclockwise loop oriented at 11 o’clock, P. griffithsi, holotype, Mauritius, [3157 H] (MNHN-IM-2000-35265). Scale bars: 2 mm (A, B), 5 mm (C–G), 3 mm (H, I).

DNA extraction and PCR amplification

DNA was extracted using a phenol-chloroform extraction protocol with cetyltrimethyl-ammonium bromide (CTAB). The mitochondrial cytochrome c oxidase I region (COI) and 16S region were amplified using the following universal primers (all 5’-3’): LCO1490 GGT CAA CAA ATC ATA AAG ATA TTG G, and HCO2198 TAA ACT TCA GGG TGA CCA AAR AAY CA (Folmer et al. 1994), 16Sar-L CGC CTG TTT ATC AAA AAC AT (Palumbi 1996), and the modified Palumbi primer 16S 972R CCG GTC TGA ACT CAG ATC ATG T (Dayrat et al. 2011). The nuclear ITS2 and 28S regions were amplified with the following primers: LSU-1 CTA GCT GCG AGA ATT AAT GTG A, and LSU-3 ACT TTC CCT CAC GGT ACT TG (Wade and Mordan 2000), 28SC1 ACC CGC TGA ATT TAA GCA T (Hassouna et al. 1984), and 28SD3 GAC GAT CGA TTT GCA CGT CA (Vonnemann et al. 2005). The 25 μl PCRs for COI and 16S contained 15.8 μl of water, 2.5 μl of 10× PCR Buffer, 1.5 μl of 25 mM MgCl2, 0.5 μl of each 10 μM primer, 2 μl of dNTP Mixture, 0.2 μl (1 unit) of TaKaRa Taq (Code No. R001A), 1 μl of 20 ng/μl template DNA, and 1 μl of 100× BSA (Bovine Serum Albumin). The PCRs for ITS2 used the reagents in the same amounts as COI and 16S, except that water was reduced to 14.8 μl and the amount of 100× BSA was increased to 2 μl. The PCRs for 28S included 14.8 μl of water, 2.5 μl of 10× PCR Buffer, 0.5 μl of each 10 μM primer, 1 μl of dNTP Mixture, 5 μl of Q solution (which includes MgCl2) and 0.5 μl of 20 ng/μl template DNA. The thermoprofile used for COI and 16S was: 5 minutes at 94 °C; 30 cycles of 40 seconds at 94 °C, 1 minute at 46 °C, and 1 minute at 72 °C; and a final extension of 10 minutes at 72 °C. The ITS2 thermoprofile was: 1 minute at 96 °C; 35 cycles of 30 seconds at 94 °C, 30 seconds at 50 °C, and 1 minute at 72 °C; and a final extension of 10 minutes at 72 °C. The 28S thermoprofile was: 4 minutes at 94 °C; 38 cycles of 50 seconds at 94 °C, 1 minute at 52 °C, and 2 minutes 30 seconds at 72 °C; and a final extension of 10 minutes at 72 °C. The PCR products were cleaned with ExoSAP-IT (Affymetrix, Santa Clara, CA, USA) prior to sequencing. Untrimmed sequenced fragments represented approximately 680 bp for COI, 530 bp for 16S, 740 bp for ITS2, and 1030 bp for 28S.

Phylogenetic analyses

Chromatograms were consulted to resolve rare ambiguous base calls. DNA sequences were aligned using Clustal W in MEGA 7 (Kumar et al. 2016). Eleven onchidiid species outside Peronia were selected as outgroups from our previous studies (Dayrat et al. 2011, 2016, 2017, 2018, 2019a, b, c, d; Dayrat and Goulding 2017; Goulding et al. 2018a, b, c): Alionchis jailoloensis Goulding & Dayrat in Goulding et al. 2018a, Laspionchis boucheti Dayrat & Goulding in Dayrat et al. 2019b; Marmaronchis vaigiensis (Quoy & Gaimard, 1825), Melayonchis eloisae Dayrat in Dayrat et al. 2017, Onchidella celtica (Cuvier in Audouin and Milne-Edwards 1832), Onchidina australis (Semper, 1880), Onchidium typhae Buchannan, 1800, Paromoionchis tumidus (Semper, 1880), Peronina tenera (Stoliczka, 1869), Platevindex luteus (Semper, 1880), and Wallaconchis sinanui Goulding & Dayrat in Goulding et al. 2018b. All new DNA sequences were deposited in GenBank and vouchers deposited in museum collections (Table 2). The ends of each alignment were trimmed. Alignments of mitochondrial (COI and 16S) sequences and nuclear (ITS2 and 28S) sequences were concatenated separately in order to test whether these two data sets support the same relationships. The concatenated mitochondrial alignment included 1014 nucleotide positions: 614 (COI) and 400 (16S). The concatenated ITS2 and 28S alignment included 1544 nucleotide positions: 535 (ITS2) and 1009 (28S). The haplotype ITS2 alignment (in which identical sequences were grouped into a single haplotype sequence) included 740 nucleotide positions.

Three independent sets of phylogenetic analyses were performed: 1) Maximum Likelihood and Bayesian analyses with concatenated mitochondrial COI and 16S sequences; 2) Maximum Parsimony analyses with concatenated nuclear ITS2 and 28S sequences; 3) Maximum Parsimony analyses with ITS2 haplotype sequences. Maximum Parsimony analyses were conducted in PAUP v 4.0 (Swofford 2002) with gaps coded as a fifth character state, and 100 bootstrap replicates conducted using a full heuristic search. Prior to Maximum Likelihood and Bayesian phylogenetic analyses, the best-fitting evolutionary model was selected for each locus separately using the Model Selection option from Topali v2.5 (Milne et al. 2004): a GTR + G model was independently selected for COI and 16S. Maximum Likelihood analyses were performed using PhyML (Guindon and Gascuel 2003) as implemented in Topali. Node support was evaluated using bootstrapping with 100 replicates. Bayesian analyses were performed using MrBayes v3.1.2 (Ronquist and Huelsenbeck 2003) as implemented in Topali, with five simultaneous runs of 1.5×106 generations each, sample frequency of 100, and burn in of 25% (and posterior probabilities were also calculated). Topali did not detect any issue with respect to convergence. All analyses were run several times and yielded the same result.

In addition, genetic distances between COI sequences were calculated in MEGA 7 as uncorrected p-distances. COI sequences were also translated into amino acid sequences in MEGA using the invertebrate mitochondrial genetic code to check for the presence of stop codons (no stop codon was found).

Results

Molecular phylogenetic analyses

The monophyly of Peronia is strongly supported in all analyses except in the mitochondrial ML analyses (bootstrap of 58), which confirms that all onchidiid slugs with dorsal gills belong to the same clade (Figs 24).

Figure 2. 

Phylogenetic relationships between Peronia species based on concatenated mitochondrial COI and 16S DNA sequences. Numbers by the branches are the bootstrap values (maximum likelihood analysis) and the posterior probabilities (Bayesian analysis). Only the values > 50% (ML) and > 0.9 (Bayesian) are indicated. Numbers for each individual correspond to unique identifiers for DNA extraction. Information on specimens can be found in the lists of material examined and in Table 2. The color used for each species or mitochondrial unit is the same as the color used in Figs 36.

Figure 2. 

Continued.

Figure 2. 

Continued.

Seven nodes of higher relationships among Peronia species are well supported. Supports are indicated here in parentheses in the following order: ML bootstrap in mitochondrial analysis, Bayesian posterior probability in mitochondrial analysis, bootstrap in ITS2 analysis, bootstrap in ITS2 and 28S analysis (bootstrap values below 50% and posterior probabilities below 0.90 are replaced by a dash). Most basally, Peronia is always split in clades A and B. Clade A is strongly supported (99, 1.0, 100, 100) and includes P. peronii and P. okinawensis. Clade B is also strongly supported (99, 1, 93, 99) and includes clade C and P. madagascariensis as its most basal species. Clade C, which is consistently recovered but moderately supported (-, -, 90, 87), includes clade D and P. platei as its most basal species. Clade D (98, 1, 99, 86) includes the three clades E, F, and G, of which the relationships are unresolved (Fig. 4) or incongruent (Figs 2, 3). Clade E (83, 0.9, 80, 54) includes P. griffithsi and P. setoensis. Clade F (100, 1.0, 75, 93) includes P. sydneyensis and P. willani. Clade G (97, 1, 71, 94) includes the five least-inclusive mitochondrial units of P. verruculata. The relationships of those five units are not resolved (all support values are very low).

Figure 3. 

Maximum parsimony consensus tree within Peronia based on ITS2 sequences (identical sequences are represented as a single haplotype sequence). Numbers by the branches are the bootstrap values. Only the values > 50% are indicated. Numbers for each individual correspond to unique identifiers for DNA extraction. Information on specimens can be found in the lists of material examined and in Table 2. The color used for each species or mitochondrial unit is the same as the color used in Figs 2, 46.

The monophyly of each species recognized here is strongly supported in all analyses, except for the special case of P. sydneyensis (see below, species delineation). Within four species, some least-inclusive units are supported by the mitochondrial markers but not by comparative anatomy and nuclear markers (Figs 24): two units within P. peronii (one unit from Mauritius and the other from the West Pacific); two units within P. platei (one unit from Hawaii and the other from Papua New Guinea); two units within P. griffithsi (one unit from Mauritius and the other from Kei Islands and Papua New Guinea); and three units of P. verruculata from South-East Asia and the West Pacific (units #1, #2, and #3). Two least-inclusive mitochondrial units within P. verruculata from the western Indian Ocean (units #4 and #5) are also monophyletic in nuclear analyses (Figs 24) but are anatomically cryptic (see below). Note that populations of P. verruculata from the Red Sea are not represented in molecular analyses (see below, species delineation).

In mitochondrial analyses (Fig. 2), P. sydneyensis and P. willani form together the strongly supported clade E and the monophyly of each species is also strongly supported. In nuclear analyses (Figs 3, 4), they also form a strongly supported clade but P. sydneyensis is paraphyletic with respect to P. willani. Both species are close geographically (P. sydneyensis is distributed in New South Wales, Queensland and New Caledonia, and P. willani is distributed in the Northern Territory) and may be the result of a recent divergence. The paraphyly in nuclear analyses most likely is the result of incomplete lineage sorting (see below, species delineation).

Figure 4. 

Maximum parsimony consensus tree within Peronia based on concatenated nuclear ITS2 and 28S sequences. Numbers by the branches are the bootstrap values. Only the values > 50% are indicated. Numbers for each individual correspond to unique identifiers for DNA extraction. Information on specimens can be found in the lists of material examined and in Table 2. The color used for each species or mitochondrial unit is the same as the color used in Figs 2, 3, 5, 6.

Pairwise genetic divergences

Pairwise genetic distances were calculated for a total of 13 units (Fig. 5, Table 3): the five mitochondrial units within P. verruculata as well as the eight other species. A barcode gap is found in all cases, apart from the mitochondrial unit #1 of P. verruculata.

Figure 5. 

Diagram to help visualize the data on pairwise genetic distances between COI sequences within and between species and mitochondrial units (P. verruculata) in Peronia (see Table 3). Ranges of minimum to maximum distances are indicated (in percentages). For instance, within P. willani, individual sequences are between 0 and 1.9% divergent; individual sequences between P. willani and the other species or units are minimally 4.3% and maximally 16.8% divergent. The colors are the same as those used in Figs 24, 6.

Table 3.

Pairwise genetic distances between mitochondrial COI sequences in Peronia. Ranges of minimum to maximum distances are indicated (in percentage). For instance, the intra-specific divergences within P. madagascariensis are between 0 and 0.6%, while the inter-specific divergences between P. griffithsi and P. madagascariensis are between 9.3 and 11.3%.

Units 1 2 3 4 5 6 7 8 9 10 11 12 13
1 P. verruculata (unit #1) 0.0–3.6
2 P. verruculata (unit #2) 3.2–6.6 0.0–1.4
3 P. verruculata (unit #3) 3.4–5.4 4.7–6.1 0.0–0.4
4 P. verruculata (unit #4) 4.9–8.2 6.6–7.3 4.9–6.0 0.0–1.2
5 P. verruculata (unit #5) 4.0–6.1 4.7–6.4 4.5–5.4 6.5–8–2 0.0–0.8
6 P. griffithsi 7.5–10.4 8.3–10.0 7.5–8.7 8.0–9.7 7.0–9.0 0.0–4.2
7 P. madagascariensis 9.3–11.3 9.3–10.6 9.5–10.3 9.2–11.0 8.5–10.0 9.3–11.3 0.0–0.6
8 P. okinawensis 12.0–14.0 12.8–13.6 12.3–13.1 13.6–14.2 11.5–12.4 13.0–14.5 12.0–12.8 0.0–0.2
9 P. peronii 11.3–15.4 11.5–14.7 12.1–14.2 12.6–15.2 12.0–14.8 11.5–15.0 12.4–15.3 8.6–9.4 0.0–4.3
10 P. platei 9.5–12.5 10.5–12.9 11.1–13.5 11.1–12.9 12.1–14.1 10.9–13.3 14.2–14.8 12.8–13.6 11.3–13.5 0.2–4.7
11 P. setoensis 7.1–8.8 8.3–8.6 7.0–7.5 6.5–7.0 8.7–9.5 5.4–7.0 11.0–11.3 13.9–14.2 11.3–14.5 10.9–12.0 0.0–0.0
12 P. sydneyensis 6.8–9.2 7.6–9.3 6.6–8.0 7.0–8.0 7.0–8.3 5.6–6.8 10.0–11.6 12.6–13.8 14.0–15.7 9.8–11.7 7.1–7.8 0.0–1.6
13 P. willani 7.3–9.2 8.3–9.1 6.1–8.0 7.5–8.9 7.8–9.3 5.9–7.5 10.3–11.4 13.8–14.6 13.8–16.8 11.4–12.2 6.5–6.6 4.3–5.4 0.0–1.9

Comparative anatomy

All Peronia slugs are characterized by dorsal gills which are not found in other onchidiids. They are also all characterized by a unique combination of internal traits: they are the only onchidiid slugs with intestinal loops of type I or V, an accessory penial gland, and no rectal gland. The fact that any slug with this combination of traits belongs to a Peronia species is helpful to identify specimens with dorsal gills retracted inside the notum.

There are no external differences between Peronia species. In the field, it is not possible to reliably identify any of them, especially because sympatric species are often found together at the exact same sites. Individuals of very large size (longer than 100 mm) are only found in P. peronii, but smaller individuals are impossible to distinguish externally from other species. Also, tall papillae over the entire notum seem to be mostly found in P. peronii and P. madagascariensis, but that may be due to the fact that slugs of both species are the largest, and it remains difficult to define exactly what a tall papilla is because papilla size is highly variable.

Internal differences help identify some species reliably, but not all (Table 4). Internal differences are almost exclusively based on combinations of traits because no Peronia species is characterized by any unique, distinctive feature, except for P. peronii (characterized by a spine of the accessory penial gland longer than 3 mm) and P. sydneyensis (characterized by strong protuberances on the spine of the accessory penial gland), and it remains difficult to identify Peronia species anatomically. For instance, where they overlap geographically (Queensland and New Caledonia), P. verruculata and P. sydneyensis can only be distinguished based on the length of the spine of the accessory penial gland, the presence of strong protuberances near the tip of the spine of the accessory penial gland, and the length of the penial hooks, which are all traits that are hardly accessible to a non-expert. However, only two Peronia species are cryptic externally and internally: P. setoensis and P. platei, which are not sister taxa (Figs 24) and do not overlap geographically, at least based upon current data (Fig. 6). Finally, the mitochondrial units of P. verruculata cannot be reliably distinguished anatomically.

Figure 6. 

Geographical distribution of the Peronia species A distribution of all Peronia species except for P. peronii B distribution of P. peronii. The colors are the same as those used in Figs 25. Colored areas correspond to hypothetical geographical ranges based on confirmed records only. Distinct colors are used for each unit of P. verruculata. The distribution of P. verruculata in the Indo-West Pacific is actually continuous. However, because it is unclear which units are present in regions from where we have no fresh material of P. verruculata (red areas), no unit of P. verruculata is shown there. For P. peronii, black dots correspond to material identified based on anatomical characters and blue dots correspond to material with DNA sequences. Details on species distribution can be found in each species description.

Types of intestinal loops are useful for the identification of Peronia species (Fig. 1): species are characterized by intestinal loops of type V (P. griffithsi, P. madagascariensis, P. platei, and P. setoensis), type I with a transitional loop oriented between 12 and 3 o’clock (P. okinawensis and P. peronii), or type I with a transitional loop oriented between 3 and 6 o’clock (P. sydneyensis, P. verruculata, P. willani). Exceptions exist but are remarkably rare: only one individual in P. sydneyensis was found with a transitional loop slightly outside the range of that species (at 2 o’clock). Types of intestinal loops, however, can only be used in combination with other traits for the purpose of species identification.

The insertion of the retractor muscle of the penis is not very useful in identification because it mostly matches the distribution of the respective intestinal loop types (Table 4). An insertion near the heart is only found in the two species with intestinal loops of type I and transitional loops oriented between 12 and 3 o’clock (P. peronii and P. okinawensis). Within each species, all individuals share the same insertion of the retractor muscle (either near the heart or at the posterior end of the visceral cavity). However, in P. griffithsi, which is widely distributed from the West Pacific to Mauritius, individuals are characterized by both insertions. In P. peronii, the retractor muscle can exceptionally be vestigial (with no clear insertion).

The length of the muscular sac of the accessory penial gland varies depending on the size of animals, but it is useful to help identify some species. Indeed, only two species (P. peronii and P. willani) are characterized by a muscular sac which is longer than 20 mm (Table 4). The length of the spine of the accessory penial gland is helpful to distinguish closely related species which, otherwise, are very similar anatomically: P. peronii (at least 3 mm) and P. okinawensis (less than 2.3 mm); P. setoensis (more than 0.9 mm) and P. griffithsi (less than 0.62 mm); and P. sydneyensis (less than 1 mm) and P. willani (more than 1.5 mm). The diameter of the spine at its base can be used in exactly the same way. The length of penial hooks also differs between species: the longest hooks are found in P. madagascariensis (up to 100 μm), the shortest in P. setoensis and P. griffithsi (less than 25 μm).

Table 4.

Summary of traits that can help identify Peronia species, based exclusively on specimens examined for the present revision. Species are arranged in a phylogenetic order (Figs 24). Traits are described in detail in species descriptions.

Species Max. animal length (mm) Papillae with dorsal eyes Intestinal type (transitional loop orientation) Retractor muscle insertion (near heart or end of visceral cavity) Muscular sac length (mm) Accessory penial gland spine length (mm) Accessory penial gland spine diameter base (μm) Accessory penial gland spine diameter tip (μm) Penis hooks length (μm) Distribution
P. peronii 140 15–20 I (12–3 o’clock) heart (exc. vestigial) >20 3.0–5.0 400–500 160–200 <50 Indo-West Pacific (Zanzibar to Okinawa and Tonga)
P. okinawensis 27 10–15 I (12–3 o’clock) heart <15 1.8–2.3 240–300 115–150 <35 Japan (Okinawa)
P. madagascariensis 80 12–18 V end of VC <15 2–2.4 200–230 70–80 <100 Western Indian Ocean
P. platei 30 7–10 V end of VC <5 0.7–1.0 65–100 20–30 <60 Western Pacific (PNG to Hawaii & French Polynesia)
P. setoensis 20 8–12 V end of VC <5 0.9–1.2 80–85 15–25 <25 Japan (Wakayama)
P. griffithsi 25 6–10 V end of VC (exc. heart) <5 0.50–0.62 60–65 15–20 <25 Indo-West Pacific (Mauritius to Kei Islands & New Ireland)
P. sydneyensis 50 8–16 I (3–6 o’clock) end of VC <10 0.6–1.0 90–100 20–50 <30 Queensland, New South Wales & New Caledonia
P. willani 65 10–25 I (3–6 o’clock) end of VC <25 1.5–1.9 240–250 80–100 <37 Northern Territory
P. verruculata #1 60 (exc. 73) 10–22 I (3–6 o’clock) end of VC <15 1.4–2.0 100–270 35–50 <50 Singapore to eastern Australia, New Caledonia & Japan
#2 55 14–22 <10 1.4–1.7 140–160 30–35 Sumatra & Andaman
#3 40 10–18 1.8–2.2 200–270 40–80 <60 Malaysia & Singapore
#4 60 (1.3) 2.2–2.8 200 50 Western India, Pakistan & Persian Gulf
#5 50 10–20 1.8–2.0 150–180 45–50 <55 Mozambique & Madagascar
#6 40 10–18 <15 2.0–2.4 140–200 55–60 Red Sea

Species delineation

The delineation of Peronia species is straightforward. They are all supported by independent data sets: they are reciprocally monophyletic with both mitochondrial and nuclear markers, and their monophyly is strongly supported; they are all separated by a large barcode gap; and they each are characterized by a unique combination of anatomical traits (with the exception of P. setoensis and P. platei, which are cryptic). Only two species need special attention: P. sydneyensis and P. verruculata.

The paraphyly of P. sydneyensis with respect to P. willani in nuclear analyses most likely is the result of incomplete lineage sorting, because lineage sorting progresses more rapidly for mitochondrial alleles than for nuclear alleles (Funk and Omland 2003). Also, P. sydneyensis and P. willani species are clearly distinct anatomically: in particular, P. sydneyensis is characterized by unique, strong protuberances near the tip of the spine of the accessory penial gland. Therefore, P. sydneyensis and P. willani are regarded as two recent but well-delineated species.

Despite some genetic structure, Peronia verruculata is regarded as a single species for various reasons. In mitochondrial analyses, P. verruculata is split in five least-inclusive mitochondrial units of which the relationships are basically unresolved due to low support (Fig. 2). In nuclear analyses, the mitochondrial units #1, #2, and #3 are not monophyletic (Figs 3, 4). Therefore, they should not be recognized as distinct taxa. In nuclear analyses, units #4 and #5 are monophyletic (Figs 3, 4). However, the mitochondrial units #1, #2, and #3 do not form a monophyletic group with respect to units #4 and #5. Recognizing mitochondrial units #4 and #5 each as a separate taxon would mean that mitochondrial units #1, #2, and #3 would also have to be recognized as separate taxa, which is unwarranted for the reasons given above.

All mitochondrial units of P. verruculata are cryptic anatomically (their anatomical traits display overlapping variation) while P. verruculata is clearly distinct from other Peronia species (Table 4). Finally, it would seem premature to recognize units #4 and #5 as independent lineages because our geographical sampling of P. verruculata is not continuous (Fig. 6). Future samples from southern India (including Sri Lanka) or the Arabian Sea (the coast of Yemen, Oman, Somalia) might show that the individuals of the western mitochondrial units #4 and #5 can still interbreed, exactly like units #1, #2, and #3. We therefore refrain from naming those five mitochondrial units within P. verruculata. They are merely regarded as mitochondrial units that indicate some genetic structure, but the current data do not suggest that they should be recognized as distinct taxa. Note that taxon names are already available for the mitochondrial units #1, #4, and #5 of P. verruculata (Table 1).

Finally, note that Peronia verruculata was described from the Red Sea, from which no fresh material could be obtained. However, the specimens examined from the Red Sea are anatomically indistinguishable from the specimens of the five mitochondrial units of P. verruculata (Table 4). Therefore, at this stage, there is no reason to think that the populations from the Red Sea belong to a distinct species and that the name P. verruculata cannot apply to the whole species from the Red Sea and South Africa all the way to the West Pacific (Japan, New Caledonia, and Queensland). At any rate, there are plenty of available names that can be used in the future if it were to be demonstrated that the populations from the Red Sea belong to a distinct species (see remarks on P. verruculata).

Species distribution

Geographic distribution is discussed in detail with each species description. The map of species distributions only illustrates the records that are regarded as correct (Fig. 6). Most of those correct records correspond to the specimens included in our molecular analyses. However, they also include types as well as historical museum specimens and records from the literature which could be positively identified using anatomical traits (e.g., intestinal loops, length of the spine of the accessory penial gland).

The secondary literature was read with great attention, especially in cases where it could provide geographical records not included in our material. Every record found in the literature is commented on (in the species remarks). Records from the literature are certainly not taken for granted because the secondary literature is plagued with two major issues. First, past authors did not always take the time to examine type specimens. For instance, Labbé (1934a) did not examine the types of Onchidium verruculatum and Onchidium peronii which are preserved at the Paris Museum (he did not list them in the material examined for these species), even though his study was almost exclusively based on material from that institution. Second, because there was no proper knowledge about intraspecific character variation, nobody knew which character could help distinguish species or not. For instance, Hoffmann’s (1928: 73) record of Peronia verruculata from Hawaii was never questioned, but Peronia slugs from Hawaii are all characterized by intestinal loops of type V, which means that they cannot belong to P. verruculata (which is characterized by intestinal loops of type I).

Systematics and anatomical descriptions

Family Onchidiidae Rafinesque, 1815

Peronia Fleming, 1822a

Onchis Férussac, 1822: xxxi. Nomen oblitum.

Peronia Fleming, 1822a: 574; Fleming 1822b: 463. Nomen protectum.

Peronia Blainville, 1824: 280 [junior homonym of Peronia Fleming, not a reference of Peronia Fleming].

Eudrastus Gistel, 1848: x.

Paraperonia Labbé, 1934a: 196.

Scaphis Labbé, 1934a: 203.

Lessonia Labbé, 1934a: 213 [junior homonym of Lessonia Swainson, 1832, replaced by Lessonina Starobogatov, 1976].

Quoya Labbé, 1934a: 216.

Lessonina Starobogatov, 1976: 211.

Quoyella Starobogatov, 1976: 211 [unnecessary replacement name for Quoya Labbé, 1934a].

Type species

Onchis: Onchidium peronii Cuvier, 1804, by monotypy.

Peronia Fleming: Onchidium peronii Cuvier, 1804, by monotypy.

Peronia Blainville: Peronia mauritiana Blainville, 1824, by original designation.

Eudrastus: Onchidium tonganum Quoy & Gaimard, 1832, by subsequent designation (Baker 1938: 86).

Paraperonia: Paraperonia gondwanae Labbé, 1934a, by subsequent designation (Starobogatov 1976: 211).

Scaphis: Onchidium astridae Labbé, 1934b, by subsequent designation (Starobogatov 1976: 211).

Quoya: Quoya indica Labbé, 1934a, by monotypy.

Lessonina: Onchidium ferrugineum Lesson, 1831a, by monotypy.

Quoyella: Quoya indica Labbé, 1934a, by monotypy.

Etymology

Onchis: After the Greek ὁ ὂγκος, oncos, which means mass, or tumor.

Peronia: After François Péron [1775–1810], zoologist of the Baudin expedition between 1800 and 1803, during which he collected the two slugs (from Mauritius and Timor) which Cuvier described as Onchidium peronii in 1804.

Eudrastus: Likely, although for unclear reasons, from the Greek εὖ, eu, for true, and δραστέoς, drasteos, a verbal adjective which means to be done.

Paraperonia: From the Greek παρα, para, meaning beside, and Peronia.

Scaphis: After the Greek ἡ σκᾰφίs, which means small boat (Labbé, 1934a: 202).

Quoya: After the French naturalist Jean René Constant Quoy [1790–1869], a member of two circumnavigations from 1817 to 1820 with captain Freycinet and from 1826 to 1829 with captain Dumont d’Urville. Quoy and Joseph Paul Gaimard [1793–1858] described several species of onchidiids based on their collections in the southern seas. Quoyella has the same etymology.

Lessonina: After the French naturalist René Primevère Lesson [1794–1849], a member of a circumnavigation from 1822 to 1825 with captain Duperrey. Lesson described several species of onchidiids based on his collections in the southern seas, such as the type species of Lessonina, Onchidium ferrugineum, which he collected in West Papua, Indonesia. Labbé’s invalid name Lessonia was also dedicated to Lesson.

Gender

Onchis: Masculine. Férussac did not specify the gender of Onchis which he did not combine with any specific name, and even the binomen Onchis peronii, which Férussac did not use per se, would not help in that respect. Because Onchis is derived from the masculine Greek noun ὁ ὂγκος, it is considered to be of masculine gender.

Peronia: Feminine. No gender was specified by Fleming, and the combination Peronia peronii does not help to determine it. Because no gender was originally specified or indicated and because Peronia ends in -a, it is treated as a name of feminine gender (ICZN 1999: Article 30.2.4). Indeed, Peronia mauritiana, an early combination used by Blainville (1824: 281), shows that Peronia has always been treated as a name of feminine gender.

Eudrastus: Masculine. No gender was originally specified or indicated. Eudrastus ends in a word derived from a word of variable gender (a verbal adjective) and should be treated as masculine (ICZN 1999: Article 30.1.4.2).

Paraperonia: Feminine. Gender of Peronia.

Scaphis: Feminine. The gender was not specified by Labbé, but his original combinations S. atra, S. carbonaria, S. lata, and S. punctata indicate that he treated Scaphis as a name of feminine gender, which is correct since Scaphis is derived from the feminine Greek noun ἡ σκᾰφίs.

Quoya: Feminine. The gender was not specified by Labbé, but his original combination Q. indica indicates that he treated Quoya as a name of feminine gender, which is assumed to be the gender of Quoyella as well.

Lessonina: Feminine. The gender was not specified by Starobogatov, and no gender was specified for Lessonia by Labbé. Labbé’s original combination Lessonia ferruginea indicates that he treated Lessonia as a name of feminine gender, which is assumed to be the gender of Lessonina as well.

Diagnosis

Body not flattened. Dorsal gills present. Dorsal eyes present. No retractable, central papilla present. Eyes at tip of short ocular tentacles. Male opening below right ocular tentacle and to its left. Foot wide. Pneumostome median, on ventral hyponotum. Intestinal loops of types I or V. Rectal gland absent. Accessory penial gland present, with muscular sac. Penis with hooks.

Remarks

Phylogenetic analyses show that all species of slugs with dorsal gills belong to the same clade (Figs 24). Seven generic names apply to that clade (excluding spelling mistakes, unjustified emendations, replaced names, and Peronia Blainville, 1824, a junior homonym of Peronia Fleming, 1822a). Note that the species name of a type species can be valid (such as Peronia peronii), synonymous (such as Onchidium tonganum, junior synonym of P. peronii), or even a nomen dubium (such as Quoya indica). Remarks on the nomenclatural history of the genus Peronia follow a chronological order.

Cuvier (1804) described the first Peronia species as Onchidium peronii but did not mention the presence of dorsal gills. Nor did he illustrate them. He only described a mantle covered by small warts subdivided in even smaller warts. Dorsal gills are actually present on the dorsum of the type specimen of Onchidium peronii from Timor, but they are retracted, as most often seen in preserved specimens. Cuvier (1804: 41) also confessed that he would have believed O. peronii to be terrestrial, due to its pulmonary cavity “similar to that of reptiles”, but that he regarded it as marine because Péron was certain to have collected it in seawater. But, Cuvier (1804: 41) adds: “I think at least that it comes to the surface to open its [pulmonary] hole, and naturally take air to breathe, as do our bulines [Bulinus] and our planorbes [Planorbis] which, although aquatic, breathe only air.” Actually, Peronia slugs hide in crevices at high tide and only come out at low tide.

Cuvier (1804: 38) decided to classify his new species in Buchannan’s (1800) genus Onchidium because of the “extreme external resemblance” between O. peronii and Buchannan’s O. typhae, despite the fact that, according to Buchannan, sexes are separate in O. typhae, while Cuvier’s O. peronii is hermaphroditic. In his description of O. typhae, Buchannan (1800) wrote that slugs live in Bengal on leaves of Typha reeds and are “very nearly allied” to Limax, suggesting that they are terrestrial, although he did not mention the presence of a pulmonary cavity and did not clearly state whether the slugs were terrestrial or not. At any rate, authors considered that Buchannan’s (1800) O. typhae was not a marine species and Blainville (1817: 440) argued that Buchannan’s O. typhae was “generically” different from Cuvier’s O. peronii, and that Onchidium should be restricted to O. typhae. However, Blainville (1817) did not propose any new generic name for Cuvier’s (1804) Onchidium peronii.

In his Histoire naturelle générale et particulière des mollusques terrestres et fluviatiles, Férussac (1819: 80–82) agreed with Blainville (1817) that Cuvier’s (1804) Onchidium peronii was distinct from Buchannan’s (1800) O. typhae, but, like Blainville, he refrained from creating a new generic name for O. peronii. A year later, Fleming (1820: 616) stated that he thought Cuvier’s O. peronii should probably be classified in a different genus from Buchannan’s Onchidium: “This species [Onchidium typhae Buchannan], however, if the description be accurate, differs essentially from the one described by Cuvier [Onchidium peronii], and would lead us to infer that a new genus would be necessary for the reception of the species of the last-mentioned naturalist.”

The two generic names Onchis and Peronia were independently created in 1822 for O. peronii, respectively by Férussac (1822) and Fleming (1822a, b) who both follow Blainville’s (1817) argument according to which a marine and hermaphroditic species (O. peronii) cannot be classified in the same genus as a terrestrial species with separate sexes (O. typhae). Interestingly, neither Férussac (1822) nor Fleming (1822a, b) mention dorsal gills (which, again, Cuvier did not mention in the original description of O. peronii). Dorsal gills were first illustrated by Savigny (1817: pl. 2, fig. 3.5) in the Description de l’Egypte for slugs from the Red Sea; for a collation, see Baring (1838) and Sherborn (1897). However, gills remained completely unnoticed because the explanation of Savigny’s plate was published nearly ten years later by Audouin (1826: 18–20).

The exact date of publication of Onchis is 13 April 1822 (when the pages xxv–xlvii were published); a collation for Férussac’s (1821–1822) Tableaux can be found in Coan and Kabat (2019). Férussac (1822: xxxi) clearly distinguishes two genera of onchidiids: “Genre I. Onchide, Onchis; Onchidium, Cuvier, Ocken. (Marin.)” and “Genre II. Onchidie, Onchidium, Buchannan, Ocken.” Note that Oken (1815: 307), to which Férussac (1822) refers, merely listed Onchidium typhae and O. peronii. According to Férussac, Onchis clearly refers to Cuvier’s Onchidium peronii, supposedly marine and living underwater, and Onchidium is restricted to Buchannan’s Onchidium typhae, thought not to live underwater. In the Tableau systématique de la famille de limaces (part of the 16th livraison published on 13 July 1822), Férussac (1822: 8) also considered two genera: the “premier genre,” i.e., the first genus ever described, Buchannan’s Onchidium, and another genus, unnamed, with Onchidium peronii as type.

Onchis is not etymologically rigorous. The latinization of ὂγκος is oncos or oncus, as in the English word oncology. The Greek letter κ is “c” in Latin, while χ becomes “ch.” That Férussac used onchis instead of oncos is not surprising, as naturalists often took liberties with the latinization of Greek words. A famous example being the word taxonomy, created as taxonomie by De Candolle (1813: 19) from the Greek words taxis (arrangement, order) and nomos (law, rule): taxis should have stayed as taxi- to form taxinomie, taxinomy, exactly like in the English word taxidermy (from taxis and dermis, skin). However, the Code does not require taxon names to be etymologically correct. Therefore, the intentional spelling change of Onchis to Oncus by Agassiz (1846: 259; 1848: 748) is an unjustified emendation because Onchis is not the result of “inadvertent error, such as a lapsus calami or a copyist’s or printer’s error” (ICZN 1999: Article 32.5.1) and therefore Onchis must not be corrected. The emendation of Onchidium into Oncidium by Agassiz (1846: 259; 1848: 748) also is unjustified for the same reason.

The generic name Peronia first appeared in two different venues, both published by Fleming (1822). One venue is Fleming’s (1822a: 574) article “Mollusca” in the fifth volume (second part) of the Supplement to the fourth, fifth, and sixth editions of the Encyclopædia Britannica published in May 1822 (as clearly indicated in a memorandum at the end of the sixth volume of the Supplement), even though the Supplement was only completed in 1824 (date on the title page). The other venue is Fleming’s (1822b: 463) Philosophy of Zoology which, according to Feuer and Smith (1972: 55), was not published earlier than May 1822 but no later than June 1822. The mention of Peronia in the Supplement is considered here to be the earliest one because it was published in May 1822.

Peronia Fleming, 1822a is an objective junior synonym of Onchis Férussac, 1822, because Férussac’s Onchis was published prior to Fleming’s Peronia and both generic names share the same type species (Onchidium peronii). However, to the best of our knowledge, Onchis has only been used twice in a binomen, and both times before 1899: by Stimpson (1855) for Onchis fruticosa, a species name that has remained unnoticed until now, and by Mörch (1863) for Onchis (Peronella) armadilla Mörch, 1863, i.e., Onchidella armadilla (Mörch, 1863). Reversal of precedence applies here (ICZN 1999: Article 23.9). Onchis, the senior synonym, “has not been used as a valid name after 1899” (ICZN 1999: Article 23.9.1.1) and Peronia, the junior synonym, “has been used for a particular taxon, as its presumed valid name, in at least 25 works, published by at least 10 authors in the immediately preceding 50 years and encompassing a span of not less than 10 years.” (ICZN 1999: Article 23.9.1.2) A chronological list of 25 works meeting the criteria of ICZN Article 23.9.1.2 is provided here, all of which mentioning Peronia, Peronia verruculata, or Peronia peronii as valid names: Marcus and Marcus (1970), Starobogatov (1976), Britton (1984), Biskupiak and Ireland (1985), Faulkner (1987), Pietra (1990), Arimoto et al. (1993), Davies-Coleman and Garson (1998), Pietra (2002), Nakaoka et al. (2006), Carbone et al. (2009), Morrisey et al. (2010), Dayrat et al. (2011), White et al. (2011), Gaitán-Espitia et al. (2013), Mandal and Harkantra (2013), Sun et al. (2014), Bitaab et al. (2015), Harasewych et al. (2015), Liu et al. (2015), Wardiatno et al. (2015), Sun et al. (2016), Santhosh Kumar et al. (2016), Solanki et al. (2017), Xu et al. (2018). Onchis Férussac, 1822, objective senior synonym, is regarded as a nomen oblitum, and Peronia Fleming, 1822a, objective junior synonym, is regarded as a nomen protectum (ICZN 1999: Article 23.9.1.2).

Fleming (1822a: 571, 574) classified Onchidium (with only the type species O. typhae) in a group of slugs that “reside constantly on the land,” and transferred O. peronii to Peronia, a genus for marine slugs that have “their residence constantly in water” and look like Onchidium. However, Fleming (1822a: 574) expressed doubts that Peronia slugs are air-breathing, as Cuvier (1804) claimed in the original description of O. peronii:

“This genus, which we have named in honor of M. Peron, was referred by Cuvier to the Onchidium of Buchanan (…) and the species termed O. Peronii. It was found creeping upon marine rocks, under water, at the Mauritius, by M. Peron. M. Cuvier conjectures that it breathes free air, and has accordingly inserted it among the Pulmones aquatique [Pulmonés aquatiques, i.e., aquatic pulmonates]. Some doubts, however, may reasonably be entertained about the truth of this supposition. It would certainly be an unexpected occurrence to find a marine gasteropodous mollusca obliged to come to the surface at intervals to respire. It will probably be found that it is truly branchiferous.”

It was Audouin (1826) who demonstrated later that both Cuvier and Fleming were correct because Peronia peronii can breathe through both its pulmonary cavity and dorsal gills.

Blainville (1824: 280) created the generic name Peronia without being aware that Fleming (1822a, b) had already created exactly the same name two years before. Indeed, that Blainville (1824: 258) wrote “our genus Péronie” clearly suggests that he thought he was the author of Peronia. Also, most past authors attributed the authorship of Peronia to Blainville instead of Fleming (e.g., Stoliczka 1869: 100; Plate 1893: 102; Labbé 1934a: 189). Peronia Blainville, 1824 is a junior homonym of Peronia Fleming, 1822a and thus cannot be used as a valid name (ICZN 1999: Article 52.2). However, Peronia Blainville is also a junior objective synonym of Peronia Fleming, because they “both denote nominal taxa with name-bearing types whose own names are themselves objectively synonymous.” (ICZN 1999: “objective synonym” in the glossary) Indeed, O. peronii, the type species of Peronia Fleming, and P. mauritiana, the type species of Peronia Blainville are objective synonyms because they share the same lectotype, i.e., the specimen from Mauritius which Cuvier (1804: pl. 6) illustrated (see below, the comments on the type material of O. peronii and P. mauritiana).

When he created the generic name Peronia, Blainville (1824: 280, 281) cited only one species name, Peronia mauritiana, a junior objective synonym of Onchidium peronii. Blainville (1824: 281) also claimed that he knew four or five other species of marine onchidiids from the southern hemisphere, without naming them, but Blainville (1826: 523) listed them two years later (Table 1): Peronia laevis, a junior objective synonym of Marmaronchis vaigiensis; Peronia semituberculata, a junior objective synonym of Onchidium planatum, itself a nomen dubium which may or may not refer to an onchidiid species; Peronia oniscoides, which all authors ignored except for Labbé (1934a: 243) and which clearly does not refer to a Peronia species (see general discussion). In addition, Blainville (1826: 523) also pointed out that Onchidium celticum, a name which Cuvier used for small marine slugs from the coast of Brittany, France, could also refer to a Peronia; Onchidium celticum remained a nomen nudum until 1832, when it was described by Audouin and Milne-Edwards (1832: 118).

Like Cuvier (1804), Férussac (1822), and Fleming (1822a, b), Blainville (1824) did not mention the existence of dorsal gills. Dorsal gills were first described by Audouin (1826: 18–20) in the explanation of a plate by Savigny (1817: pl. 2) from the Description de l’Egypte. Savigny’s (1817: pl. 2, figs 3.1–3.8) plate displays eight drawings for two onchidiid slugs from the Red Sea, with one of them clearly representing a dorsal gill (Savigny 1817: pl. 2, fig. 3.5). According to Audouin (1826: 19), it was Cuvier himself who identified those two slugs as Onchidium peronii, although Cuvier (1830) later changed his mind and created the new name Onchidium verruculatum for them. More importantly, Audouin (1826: 19) described in great detail the “small vascular branches” at the posterior end of the dorsum, or “tubercles” that work as “true gills.” And Audouin (1826: 19) even made this clever statement:

“The Onchidie thus would have at the same time a pulmonary apparatus and a branchial apparatus; and that structure is in perfect agreement with what we know of the habits of that mollusk: Péron says that it is aquatic; on the contrary M. Cuvier, without the authority of this observer, would have believed it to be terrestrial. (...) We think that the Onchidie, at least the species illustrated here, enjoys the capacity to breathe under water thanks to the help of those ramified tubercles which cover the posterior end of its body, without the necessity of coming up to the surface; which is relatively difficult for an animal that slowly crawls at the bottom underwater. As for the pulmonary opening, it indicates that the onchidie breathes air as well; and we must suppose that several times in its life it finds itself in the condition to do so.”

Audouin supposedly assumed that those slugs were truly aquatic.

Because Peronia was originally used as a genus for all marine onchidiids by both Fleming (1822a, b) and Blainville (1824, 1826), several Peronia species names already existed by 1830: Peronia mauritiana, P. peronii, P. oniscoides, P. semituberculata, and P. laevis (see above). Of those names, only the two objective synonyms P. mauritiana and P. peronii refer to true Peronia slugs, i.e., slugs with dorsal gills (Table 1). Cuvier (1830: 46) did not see the need for a genus assignment for marine onchidiid species and still only recognized Onchidium, but other naturalists started transferring species names from Onchidium to Peronia. Lesson (1833: pl. 19) transferred his own Onchidium ferrugineum Lesson, 1831a to Peronia, and clearly specified that he agreed with Blainville that marine onchidiids should be classified in a distinct genus. Dorsal gills are very clearly described by Lesson (1831a: 128–130; 1831b: 300–302; 1832: 36–37, fig. 32; 1833: pl. 19) in O. ferrugineum, but they were not the reason why he transferred it from Onchidium to Peronia. Shortly after that, Oken (1834a) also transferred six Onchidium species names by Quoy and Gaimard (1832–1833) to Peronia (P. cinerea, P. incisa, P. nigricans, P. patelloides, P. punctata, and P. tongana), with no justification but most likely because he also adopted the idea that marine onchidiids should not be classified in Onchidium.

The name Eudrastus was created by Gistel (1848: x), as a replacement name for “Peronia (Quoy, Isis 1834. 287.).” Gistel refers here to a report (Oken 1834a: 283–310) on Quoy and Gaimard’s (1832–1833) contribution to the Voyage de découvertes de l’Astrolabe published in Isis, the encyclopedic journal edited by Lorenz Oken from 1817 to 1848. This report was most likely written by Oken himself, as was often the case (Kertesz 1986), which would explain that the six onchidiid specific names mentioned (tongana, incisa, patelloides, nigricans, punctata, cinerea) are combined with Peronia instead of Onchidium, the generic name originally used by Quoy and Gaimard (1832–1833). Regardless of who authored that Isis report, Gistel (1848) did create the new generic name Eudrastus for those six species. Baker (1938: 86) subsequently designated Onchidium tonganum Quoy & Gaimard, 1832 (Peronia tongana in Isis), as the type species of Eudrastus. Onchidium tonganum is regarded here as a junior subjective synonym of Peronia peronii, so Eudrastus is a junior subjective synonym of Peronia. Britton (1984: 182–183) suggested that Eudrastus should be regarded as a junior synonym of Peronia because it seemed to be based on “unimportant characters.”

John Edwards Gray (1847: 179) attributed the authorship of Peronia to Blainville (with an erroneous date of 1825) but, most importantly, gave its modern definition to Peronia by restricting it to six species of slugs with “radiating processes” on the back (JE Gray 1850: 117): P. alderi, P. ferruginea, P. mauritiana, P. peronii, P. punctata, and P. tongana. All those names refer to true Peronia slugs with dorsal gills. JE Gray (1850: 117) restricted Onchidium to Buchannan’s O. typhae and included all the other marine species without dorsal gills in a new genus Onchidella.

JE Gray’s (1850) clarity only lasted for a few years. Indeed, Adams and Adams (1855: 234) pointed out that Peronia slugs differ from Onchidium and Onchidella because of “arbusculiform and other appendages of the mantle, which have sometimes been mistaken for gills.” Because they did not believe that gills were distinct from other dorsal papillae, Adams and Adams (1855: 234) classified in Peronia some names that belong to both Peronia (P. ferruginea, P. mauritiana, P. peronii, P. punctata, P. tongana) and to Onchidella (O. celtica, O. indolens, O. marginata, and O. parthenopeia).

JE Gray’s (1850) classification was adopted by Keferstein (1865a) but, until Labbé’s (1934a) work, all authors have ignored the genus Peronia and simply used the genus Onchidium for slugs with and without dorsal gills (Stoliczka 1869; Semper 1880–1885; Plate 1893; Bretnall 1919; Hoffmann 1928). Stoliczka (1869: 100–102), who was the first one to re-examine live slugs of O. typhae since Buchannan (1800), firmly argued that slugs with “dorsal tufts” were anatomically so similar to Onchidium and Onchidella that only one name, Onchidium, was needed. Stoliczka (1869: 98) also clarified that O. typhae is not a terrestrial species but that, instead, it lives in “damp places, generally close to tanks or ditches, especially those which are supplied during high tide with brackish water.”

Stoliczka’s (1869) strong influence can be seen in Semper’s (1880–1885) study of the onchidiids from the Philippines (and other parts of the Indo-West Pacific) in which all onchidiids are in Onchidium, with the exception of a single species in his new genus Onchidina Semper, 1882; for a collation of Semper’s work, see Johnson (1969). Plate (1893) adopted a classification with five genera, but the four species of slugs with dorsal gills recognized by Plate are classified in Onchidium with thirteen species of slugs without dorsal gills. Hoffmann (1928) adopted a classification with six genera, six species of slugs with dorsal gills being classified in Onchidium with 34 species without dorsal gills.

Then, suddenly, in 1934, the number of onchidiid taxon names for slugs with dorsal gills dramatically increased. Based on the onchidiid collection at the Paris Museum, Labbé (1934a) created fourteen new species-group names for slugs with dorsal gills (all but one name are species names) and four new generic names: Lessonia (later replaced by Lessonina), Paraperonia, Quoya, and Scaphis. Below, the nomenclatural status of Labbé’s generic names is justified first (they all are junior synonyms of Peronia), followed by opinions in the secondary literature.

The generic name Paraperonia was created by Labbé (1934a: 196) for four species similar to Peronia but with intestinal loops of type V (instead of type I). The type species is Paraperonia gondwanae Labbé, 1934a, by subsequent designation (Starobogatov 1976: 211). Labbé’s description of Paraperonia gondwanae was based on 38 individuals with intestinal loops of types I and V which belong to different species. The application of the name P. gondwanae is clarified through the designation of a lectotype (see P. verruculata): Paraperonia gondwanae is a junior synonym of Peronia verruculata, and Paraperonia is a junior synonym of Peronia.

The generic name Scaphis was created by Labbé (1934a: 203) for nine species similar to Peronia but supposedly with an oblique, almost vertical hyponotum. The type species is Onchidium astridae Labbé, 1934b, by subsequent designation (Starobogatov 1976: 211). Onchidium astridae is a junior synonym of Peronia verruculata, and Scaphis is a junior synonym of Peronia.

Lessonia Labbé, 1934a is objectively invalid because it is the junior homonym of Lessonia Swainson, 1832 [Aves]. Starobogatov (1976: 211) replaced it by Lessonina. Labbé (1934a: 213–216, figs 48–50) described Lessonia based on a single species, Onchidium ferrugineum Lesson, 1831a, of which he examined no other material than the four syntypes (MNHN-IM-2000-22951). The examination of the three remaining syntypes (one syntype was lost by or after Labbé) revealed that the lectotype (Goulding et al. 2018b: 75) belongs to a Peronia species and that the two paralectotypes belong to Wallaconchis ater (Lesson, 1831a). Both Lesson’s original description of Onchidium ferrugineum and Labbé’s re-description of Lessonina ferruginea are a confusing combination of traits that characterize species from two distinct genera. For instance, the dorsal gills mentioned by both authors, are characteristic of Peronia, while the absence of an accessory penial gland mentioned by Labbé (even though there is a penial gland in the lectotype) is characteristic of Wallaconchis. Thanks to the designation of a lectotype with dorsal gills, the name Onchidium ferrugineum clearly applies to a Peronia species and Lessonina becomes a junior synonym of Peronia.

Starobogatov (1976: 211) created Quoyella as a replacement name of Quoya Labbé, 1934a, which he treated as a junior homonym of “Quoya Deshayes, 1843” [Mollusca, Gastropoda, Planaxidae]. In the second edition of Lamarck’s Histoire naturelle des animaux sans vertèbres, Deshayes indicates that he originally thought of creating a new genus Quoya but that, after all, he decided not to (Deshayes and Milne-Edwards 1845: 236). Deshayes still used the binomen “Planaxis decollata Quoy” (Deshayes and Milne-Edwards 1845: 238). However, in the Explication des planches of his Traité élémentaire de conchyliologie, Deshayes (1853: 50) used Quoya for two valid species names: Quoya decollata and Quoya grateloupi. Regardless, according to Gray (1847: 138), the generic name Quoya by Deshayes is an incorrect subsequent spelling of his Quoyia JE Gray, 1839. As an incorrect subsequent spelling, Quoya Deshayes is not available (ICZN 1999: Article 33.3) and, as a result, Quoyella is an unnecessary replacement name. Ironically, Gray (1847: 138) indicated that he originally found the generic name Quoyia in a manuscript by Deshayes in 1830 (“Quoyia, Desh. MSS. 1830; Gray, 1839 (...) Quoya, Desh. 1843”). According to Baker (1938: 87), Quoya Agassiz, 1862 [Coelenterata] is another homonym of Quoya Labbé, 1834a. However, the spelling of that generic name is not Quoya but Quoyia (Agassiz, 1862: 173). So, Quoyia Agassiz, 1862 is a junior homonym of Quoyia Gray, 1839, but Quoya Labbé, 1934a is not a junior homonym of Quoyia. Quoya indica Labbé, 1934a, type species of Quoya by monotypy, is regarded here as a nomen dubium even though it applies to a species with dorsal gills and thus belongs to Peronia (see general discussion).

Nothing is ever simple in onchidiid taxonomy. Indeed, Labbé (1935a, b) also described what he called “microgills” in Elophilus Labbé, 1935a, a name preoccupied by Elophilus Meigen, 1803 (Diptera) and replaced by Labbella Starobogatov, 1970. Labbé’s (1935a, b) microgills consolidated the old idea of a gradual continuum between regular dorsal papillae and dorsal gills. So, for instance, Marcus and Marcus (1960: 875) argued that one cannot say for sure whether a papilla is a dorsal gill or not. However, Dayrat et al. (2016, 2019d) demonstrated that there are no gills at all (not even microgills) on the notum of the type material of the type species of Labbella which actually belongs to Onchidium stuxbergi (Westerlund, 1883). Labbella is a junior synonym of Onchidium. Contrary to regular papillae, dorsal gills are distinctively branched, which is striking if specimens are fully relaxed before preservation but otherwise difficult to see. Finally, note that Labbé (1935b: 320) claimed that he observed rudimentary eyes on dorsal gills, which, to our knowledge, has never been confirmed.

Labbé (1934a: 187, 188) rightly recognized the importance of dorsal gills for classification and he separated all five genera of slugs with dorsal gills from all other onchidiids. According to Labbé, onchidiids deserved their own order, the Silicodermatae, composed of two suborders: Dendrobranchiatae (onchidiids with dorsal gills) and Abranchiatae (onchidiids without dorsal gills). Our phylogenetic analyses clearly demonstrate that all species of slugs with dorsal gills belong to a single clade, and that only one generic name (Peronia) is necessary (Figs 24). However, the species of slugs with no dorsal gills do not form a natural group (Figs 24). In other words, the absence of dorsal gills is a plesiomorphic trait for the onchidiids and the presence of dorsal gills is a synapomorphy for the genus Peronia.

Labbé’s (1934a: 187) distinction between the tribes Peroniidae (Peronia and Paraperonia) and Scaphidae (Scaphis, Lessonina, Quoya) based on the orientation of the hyponotum (horizontal versus oblique) is meaningless. This trait obviously varies depending on preservation, and Labbé exclusively studied preserved material from the collections of the MNHN without access to live animals.

Labbé’s (1934a: 187) distinction between Peronia and Paraperonia based on the intestinal types (type I in Peronia and type V in Paraperonia) is unwarranted because Peronia species with intestinal loops of type V are not more closely-related to each other (Table 4, Figs 24). Also, Labbé often made mistakes with respect to intestinal types: for instance, the type material of Paraperonia gondwanae includes individuals with loops of both types I and V, even though Labbé described it as a species with loops of type V. Labbé asserted that the position of the pneumostome and the size of the muscular sac differ between Peronia and Paraperonia. However, the position of the pneumostome varies between individuals and is not consistently on the right side of the median axis in species he classified as Paraperonia.

Labbé’s (1934a: 187) distinction between Scaphis, Quoya, and Lessonina, is also unwarranted. Again, the position of the pneumostome (on the right of a median line in Scaphis according to Labbé) varies between individuals. Labbé’s (1934a) re-description of Lessonina ferruginea (the type species of Lessonina, by monotypy) was based on individuals of two different species (see above). The male opening of the lectotype, which bears dorsal gills, is on the left of the right ocular tentacle, exactly as in all Peronia species, while the male opening of the two paralectotypes, which belong to Wallaconchis ater, is under the right ocular tentacle (Goulding et al. 2018: 75). Labbé (1934a: 216, fig. 51) described a double male opening in Quoya indica (the openings of the penis and of the accessory penial gland being supposedly separated), but this could not be confirmed in the type material. Regardless, male openings occasionally appear separated due to preservation (when the vestibule is everted) and that is by no means a trait of generic value.

Authors completely rejected Labbé’s (1934a) idea that the presence or absence of dorsal gills could be of any use in onchidiid classification (e.g., Marcus and Marcus 1960; Starobogatov 1976). Britton (1984: 180) even asserted that “the division of the group into two subordinate taxa based on this character is no longer admissible.” As for the status of Labbé’s (1934a, 1935a) generic names for slugs with dorsal gills, authors were not in agreement. Marcus and Marcus (1970: 213) regarded Peronia and Paraperonia “at most as subgenera.” Starobogatov (1976) regarded all names as valid: Lessonina, Paraperonia, Peronia, Quoyella (unnecessary replacement name for Quoya), Scaphis, and Labbella (supposedly with micro-gills). Britton (1984: 182–183) suggested that Paraperonia, Eudrastus and Scaphis should be regarded as junior synonyms of Peronia because they seemed to be based on “unimportant characters,” but treated Labbella (supposedly with micro-gills), Lessonina, and Quoyella (for Quoya) as valid. In a recent review of the application of onchidiid generic names, Dayrat et al. (2017: 1861) made it clear that all slugs with dorsal gills belong to one clade and that Eudrastus, Lessonina, Onchis, Paraperonia, Peronia, Quoyella (for Quoya), and Scaphis all refer to that clade. Note that the application of Lessonina was fully clarified when a lectotype was designated for its type species Onchidium ferrugineum (Goulding et al. 2018: 75).

Peronia peronii (Cuvier, 1804)

Figs 7, 8, 9, 10, 11, 12, 13, 14, 15, 16

Onchidium peronii Cuvier, 1804: 37–51, pl. 6, figs 1–9; Cuvier 1816: 411; Lamarck 1822: 46; Cuvier 1830: 46; Voigt 1834: 101; Deshayes 1836–1845: pl. 26, fig. 2; Deshayes and Milne-Edwards 1836: 709; JE Gray 1850: 117; ME Gray 1850: pl. 181, fig. 7; Berge 1855: 124, pl. 16, fig. 8; Plate 1893: 172–173, pl. 12, figs 85, 87, 91; Odhner 1919: 42; Hoffmann 1928: 44–45, 71–72 [in part only].

Peronia peronii (Cuvier, 1804): Fleming 1822a: 574; Fleming 1822b: 463; Keferstein 1865a: pl. CIII, fig. 1; Labbé 1934a: 190–191 [in part only]; Marcus and Marcus 1960: 877; Marcus and Marcus 1970: 213 [in part only]; Dayrat et al. 2011: 428; White et al. 2011: 4.

Onchis peronii (Cuvier, 1804): Férussac 1822: xxxi.

Peronia mauritiana Blainville, 1824: 281; Adams and Adams 1855: 235.

Onchidium tonganum Quoy & Gaimard, 1832: 210–211, pl. 15, figs 17, 18; Semper 1880: 258–260, pl. XIX, figs 2, 9, pl. XXII, figs 1, 2, 10 [in part only]; Bergh 1884a: 142–148, pl. VI, fig. 19, pl. VII, figs 1–6.

Peronia tongana (Quoy & Gaimard, 1832): Oken 1834a: 287; JE Gray 1850: 117; ME Gray, 1850: pl. 182, fig. 1, as tongensis; Adams and Adams 1855: 235, pl. LXXXI, fig. 3; Keferstein 1865a: pl. CII, fig. 20; Tapparone Canefri 1883: 214 [in part only]; Labbé 1934a: 191–192, figs 4–7 [in part only].

Onchidium punctatum Quoy & Gaimard, 1832: 215–216, pl. 15, figs 27, 28. Syn. nov.

Peronia punctata (Quoy & Gaimard, 1832): Oken 1834a: 287; JE Gray 1850: 117; ME Gray 1850: pl. 183, fig. 3; Adams and Adams 1855: 235; Chenu 1859: 474, fig. 3505; Tapparone Canefri 1883: 214.

Onchidium melanopneumon Bergh, 1884a: 129–142, pl. IV, figs 25–27, pl. V, figs 1–27, pl. VI, figs 5–18, 20–21; Joyeux-Laffuie 1885: viii–xi.

Paraperonia fidjiensis Labbé, 1934a: 197–198, figs 9–11. Syn. nov.

Peronia verruculata: Mörch 1872a: 28; Mörch 1872b: 325, as vermiculata [non Peronia verruculata (Cuvier, 1830)].

Type material

Lectotype and paralectotype (Onchidium peronii). Mauritius • lectotype, hereby designated, by means of Cuvier’s (1804: pl. 6) anatomical drawings. Timor • 1 paralectotype, 60/40 mm; F Péron leg.; MNHN-IM-2000-22938. The fact that the specimen illustrated by Cuvier cannot be located does not invalidate the lectotype designation (ICZN 1999: Article 74.4). That individual, according to Cuvier, measured approximately 140 mm long (preserved). Cuvier’s (1804: pl. 6) detailed anatomical drawings are exclusively based on the individual collected by Péron in Mauritius. Note that, although Cuvier’s (1804: pl. 6) illustrations are truly remarkable, they are flipped at 180° because, for instance, the heart and the male anterior parts are on the left. Something must have happened during the engraving or the printing. Hoffmann (1928: 71) referred to Mauritius as the “Typ-Lokalität” of Onchidium peronii but did not formally designate a lectotype for O. peronii. In case of syntypes, “the place of origin of the lectotype becomes the type locality of the nominal species-group taxon, despite any previously published statement of the type locality.” (ICZN 1999: Article 76.2)

The original description of Onchidium peronii was based on two specimens collected by Péron: the lectotype from Mauritius, of which the internal anatomy was illustrated in detail by Cuvier (1804: pl. 6), could not be located and is likely lost; the paralectotype from Timor (MNHN-IM-2000-22938) was very briefly mentioned by Cuvier (1804: 39) who merely wrote that another specimen was brought from Timor by Péron and that Onchidium peronii is present “at the two extreme ends of the Indian Ocean.” The paralectotype (60/40 mm) is well preserved even though dorsal papillae with eyes cannot be counted because their color faded. It is obvious that Cuvier did not actually use it for his detailed anatomical description and illustrations on plate 6, because it was never opened prior to the present study, except for a tiny cut near the lung. It was carefully opened on its side to draw a dorsal view of its intestinal loops of type I (Fig. 9A) and measure the length (4.5 mm) of the spine of the accessory penial gland (by transparency, so that the male copulatory apparatus was not dissected).

Lectotype (Peronia mauritiana). Mauritius • lectotype, hereby designated, by means of Cuvier’s (1804: pl. 6) anatomical drawings. The species name Peronia mauritiana was introduced by Blainville (1824: 281) for a species originally illustrated by Cuvier (1804: pl. 6) in the Annales du Muséum d’Histoire naturelle and which Cuvier named Onchidium peronii. Blainville’s reference to Cuvier’s (1804) plate 6 (“La Péronie de l’Isle-de-France [Mauritius]. Peronia mauritiana. Blainv., Cuv., Ann. du Mus., 5, pl. 6.”) serves as an indication, and Peronia mauritiana is an available binomen (ICZN 1999: Article 12.2.1). However, Cuvier’s original description of Onchidium peronii was based on two specimens, a lectotype from Mauritius and a paralectotype from Timor, but Cuvier’s (1804: pl. 6) plate of anatomical drawings exclusively illustrates the lectotype from Mauritius (see above). Because the lectotype of Peronia mauritiana also is the lectotype of Onchidium peronii, Peronia mauritiana remains what it always was, i.e., a junior objective synonym of Onchidium peronii.

Blainville also mentioned the name Peronia mauritiana in his Manuel de Malacologie et de Conchyliologie (Blainville 1825: 490) and in the article “Péronie” of the Dictionnaire des Sciences Naturelles (Blainville 1826: 523). The illustration published by Blainville (1827: pl. 46, fig. 7) in the Atlas of the Manuel differs from that published by Cuvier (1804: pl. 6, fig. 1). The specimen used by Blainville for that illustration could not be located, which does not matter much since it does not have any name-bearing function. However, it also means that, because there are two species of Peronia in Mauritius, Blainville’s (1827: pl. 46, fig. 7) illustration may or may not refer to Peronia mauritiana.

Lectotype (Onchidium tonganum). Tonga • lectotype, hereby designated, 100/60 mm; Panhi-Motou [possibly the small island of Pangaimotu]; MNHN-IM-2000-22937. It is unclear how many specimens Quoy and Gaimard (1832: 210–211, pl. 15, figs 17, 18) examined for the original description of Onchidium tonganum. They may have examined more than one individual. Regardless, it is clear that Onchidium tonganum applies to a Peronia species because the notum of the lectotype bears gills which were also illustrated in the original description. Its notum also bears fifteen dorsal papillae with eyes but others probably faded. The lectotype was dissected prior to the present study. The accessory penial gland and the penial apparatus are missing (pieces of the deferent duct remain). The intestinal loops are of type I with a transitional loop between 2 and 3 o’clock (Fig. 9B). Quoy and Gaimard (1832: 216) briefly mentioned the presence of O. tonganum in Manokwari, West Papua, Indonesia, but that record could not be confirmed (although P. peronii is known to be present there because Manokwari is the type locality of O. punctatum).

Lectotype and paralectotypes (Onchidium punctatum). Indonesia • lectotype, hereby designated, 70/60 mm; dans le port de Dorey [Manokwari harbor, West Papua]; 1829; JRC Quoy and JP Gaimard leg.; MNHN-IM-2000-22966. • 2 paralectotypes, 35/25 and 32/30 mm; same collection data as for the lectotype; MNHN-IM-2000-33701. An old label of the lectotype says “Onchidium punctatum, Q. G, Ast. pl. 15, fig. 27, de la Nouvelle Guinée, Quoy et Gaimard 1829.” That old label does not say “Dorey” (for the locality), which is only mentioned in the original description, but it clearly indicates that the lectotype was part of the type series of Onchidium punctatum. The lectotype bears dorsal gills, as illustrated by Quoy and Gaimard (1832: pl. 15, figs 27, 28). It was dissected prior to the present study, likely by Labbé (1934a: 203–204) and its penis is missing but its intestinal loops are of type I with a transitional loop at 3 o’clock (Fig. 9C). Its spine of the accessory penial gland, still in place in the animal, is 3.7 mm long.

A second jar was found with two paralectotypes (MNHN-IM-2000-33701). An old label for that second jar says “Onchidium piquetée, Q G. MM Quoy Gaimard, 1829” with no locality data. The name “Peronia” was added on the label. The number “51” also appears on another old label, which corresponds to an unknown numbering system. There also is a more recent label saying “Peronia picta QG, M. Quoy et Gaimard, 1829.” Quoy and Gaimard did not describe any onchidiid species with the specific name picta. However, the French vernacular name of Onchidium punctatum in Quoy and Gaimard’s (1832: 215) original description is “Onchidium piquetée.” So, it is likely that these two additional specimens were part of the type series of Onchidium punctatum. Both paralectotypes (35/25 and 32/30 mm) bear dorsal gills. The largest paralectotype was dissected prior to the present study, possibly by Labbé (1934a: 203, 204), and its penis is missing but its accessory penial gland remains. The small paralectotype was not dissected. Labbé (1934a: 203) listed three individuals from Port-Dorey which he (implicitly) regarded as part of the original series of Onchidium punctatum. Labbé gave the measurements for only two individuals: “a” (35/25 mm), likely the largest paralectotype; “b” (77/56 mm), likely the lectotype. In addition, in his re-description of Scaphis punctata, Labbé (1934a: 204–205) mentioned two individuals identified as Peronia and collected by Quoy and Gaimard in 1829, from an unknown locality. Those two individuals are likely within another jar found at the MNHN with the old number “48” and a label saying “Peronia M. Quoy et Gaimard 1829.” There is no reason to consider that those two unidentified individuals from the collection of Quoy and Gaimard were part of the type series of Onchidium punctatum. Finally, there is no other old material at the MNHN which could be assigned to the type series of O. punctatum. There are only three other old specimens from Port Dorey at the MNHN: the two syntypes (MNHN-IM-2000-22950) of Wallaconchis ater (Goulding et al. 2018: 63), and one specimen collected by Raffray in 1878 (with numbers “22” and “75” on the label).

Holotype (Onchidium melanopneumon). Fiji • holotype, by monotypy, 65/40 mm; Kandavu [Kadavu]; Aug 1874; HMS Challenger leg.; NHMUK 1888.5.30.39. The holotype was entirely dissected by Bergh and is now empty. Given the presence of dorsal gills, Onchidium melanopneumon clearly applies to a Peronia species.

Lectotype and paralectotypes (Paraperonia fidjiensis). Fiji • lectotype, hereby designated, 60/50 mm; 1876; Filhol leg.; MNHN-IM-2000-33692. No jar clearly labeled as the type material of Paraperonia fidjiensis was found at the MNHN, but the lectotype could be traced, and six paralectotypes could not be found at the MNHN. Labbé (1934a: 197–198, figs 9–11) described Paraperonia fidjiensis based on seven individuals from Fiji (“Iles Fidji”) collected by Filhol (Henri Filhol [1843–1902]) in 1876 and with the following sizes: 75/50 mm for six “a” individuals and 70/50 mm for a seventh “b” individual. Two jars of material collected in Fiji by Filhol in 1876 were found at the MNHN. The first jar, labeled as “Peronia [written over Oncidium] I. Fidji Mr. Filhol n°11 1876” and “71,” contains a single Peronia specimen which, given its size (60/50 mm), very likely is part of the type series of P. fidjiensis, and which is designated as the lectotype (MNHN-IM-2000-33692). Its radula and all reproductive parts are missing. Its intestinal loops are clearly of type I, with a transitional loop at ~ 1 o’clock (Fig. 9E). The second jar, labeled as “Oncidiella I. Fidji Mr. Filhol n°11 1876” and “101,” contains four poorly-preserved specimens which do not even appear to belong to Peronia, with a size (less than 30 mm) not compatible with the original description of P. fidjiensis, and which, therefore, cannot be regarded as part of the type series.

Additional material examined

Mauritius • 2 specimens 140/100 mm [5872] and 125/75 mm [5874]; La Mivoie; 20°20.659'S, 57°21.763'E; 11 Jun 2014; TC Goulding leg.; st 177, basalt rocks, at night; MNHN-IM-2019-1605. • 1 specimen 110/100 mm [3605]; Mahebourg, waterfront; 20°24.317'S, 57°42.605'E; 13 Jun 2014; TC Goulding leg.; st 178, rocky intertidal, with algae, just before sunrise; MNHN-IM-2019-1606. • 1 specimen 100/90 mm [1553]; Grand Port, east side of île Marianne; 20°22.828'S, 57°47.220'E; May 2003; O Griffiths leg.; A2518, out of water on limestone platform; MNHN-IM-2019-1607.

Mariana Islands • 1 specimen 115/80 mm [443]; Guam Island, Bile Bay; 13°17.124'N, 144°39.742'E; 23 Mar 2007; C Carlson leg.; reef margin; CASIZ 180486. • 1 specimen 85/70 mm [5840]; Guam Island, Bile Bay; 13°16.582'N, 144°39.752'E; 27 Nov 2007; C Carlson leg.; shoreline; MNHN-IM-2019-1609.

Papua New Guinea – Madang • 1 specimen 70/60 mm [5476]; Wonad Island; 05°08.1'S, 145°49.3'E; 29 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM43, night tide, sandy beach and intertidal rocks; MNHN-IM-2013-16260. • 1 specimen 65/45 mm [5477]; Wonad Island; 05°08.1'S, 145°49.3'E; 27 Nov & 09 Dec 2012; MNHN Expedition Papua Niugini leg.; st PM41, sandy beach and intertidal rocks; MNHN-IM-2013-15872. • 1 specimen 55/40 mm [5474]; Rempi Area, Barag Island; 05°01.1'S, 145°47.9'E; 15 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM25, fringing reef on narrow barrier island; MNHN-IM-2013-14054. • 1 specimen 80/60 mm [5472]; same collection data as for the preceding; MNHN-IM-2013-14052. • 1 specimen 80/70 mm [5471]; Rempi Area, South Dumduman Island; 05°00.2'S, 145°47.6'E; 9 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM 12, limestone rocky intertidal; MNHN-IM-2013-12500. – New Ireland • 1 specimen 50/40 mm [6086]; Kavieng, Lemus Island; 02°38'S, 150°37.5'E; 12–14 Jun 2014; MNHN Expedition Kavieng 2014 leg.; st KM24, mixed platform with seagrass; MNHN-IM-2013-53482.

Additional material examined

(historical museum collections). Chagos Archipelago • 1 specimen 95/65 mm; Ye Ye, Peros Banhos atoll; 24 Feb 1996; M Spalding (from N Yonow’s personal collection) leg.; exposed on shallow reef flat on rocks; MNHN-IM-2014-7992.

Fiji • 1 specimen 75/50 mm; Viti Isles; A Garrett leg.; ANSP 57967. • 1 specimen 28/25 mm; Viti Levu, Namuka; 18°08'S, 177°23'E; 18 Apr 1917; S Bock’s Pacific Expedition 1917–1918 leg.; barrier reef; SMNH 180357. • 2 specimens 23/20 mm and 15/15 mm; Viti Levu, SW Suva, Namuka; 18°08'S, 177°23'E; 16 Jun 1917; S Bock’s Pacific Expedition 1917–1918 leg.; barrier reef; SMNH 180374. • 1 specimen 37/30 mm; Viti Levu, Namuka; 18°08'S, 177°23'E; 19 Jun 1917; S Bock’s Pacific Expedition 1917–1918 leg.; SMNH 180375. • 1 specimen 80/65 mm; Viti Levu, Bau Island; 17°58'S, 178°36'E; 2 Jul 1917; S Bock’s Pacific Expedition 1917–1918 leg.; reef; SMNH 180373.

India • 2 specimens 85/55 mm and 70/50 mm; Nicobar Islands, Pulo Milo, Little Nicobar; Reinhardt, Galathea 305 leg.; NHMD 613753.

Indonesia – Java • 1 specimen 90/55 mm; Batavia [Jakarta]; 1899; C Aurivillius leg.; SMNH 180355. – Sumatra • 1 specimen 100/70 mm; Sumatra; Deshayes leg.; MNHN-IM-2012-25150. • 1 specimen 65/50 mm; west coast of Sumatra, Pulo Pasu [or Pulu Pasu]; 1891; C Aurivillius leg.; SMNH 180354. – Tanimbar • 1 specimen 60/50 mm; Jamdena Straits, West side of Mitak Island; 07°11'S, 131°28'E; 22 Jun 1970; Mariel King Memorial Expedition Moluccas MV “Pele” 1970 leg.; WAM S26723.

Kiribati • 1 specimen 35/35 mm; Gilbert Islands, Apaiang [Abaiang]; 01°49'N, 172°57'E; 12 Aug 1917; S Bock’s Pacific Expedition 1917–1918 leg.; outer reef; SMNH 180353. • 1 specimen 70/65 mm; Gilbert Islands, Tarawa; 01°26'N, 173E; 16–20 Aug 1917; S Bock’s Pacific Expedition 1917–1918 leg.; reef; SMNH 180382. • 1 specimen 65/50 mm; Gilbert Islands, Aranuka; 00N, 174E; 6 Oct 1917; S Bock’s Pacific Expedition 1917–1918 leg.; reef; SMNH 180376. • 1 specimen 70/50 mm; Gilbert Islands, Aranuka; 00N, 174E; 22 Oct 1917; S Bock’s Pacific Expedition 1917–1918 leg.; outer reef; SMNH 180377. • 1 specimen 30/25 mm; Gilbert Islands, Aranuka; 00N, 174E; 1 Nov 1917; S Bock’s Pacific Expedition 1917–1918 leg.; SMNH 180378. • 1 specimen 15/15 mm; Gilbert Islands, Aranuka; 00N, 174E; 26 Oct 1917; S Bock’s Pacific Expedition 1917–1918 leg.; outer reef; SMNH 180383. • 2 specimens 20/15 mm and 17/13 mm; Gilbert Islands, Aranuka; 00N, 174E; 26 Oct 1917; S Bock’s Pacific Expedition 1917–1918 leg.; outer reef east; SMNH 180384. • 1 specimen 15/12 mm; Gilbert Islands, Aranuka; 00°09'N, 173°35'E; 1917; S Bock’s Pacific Expedition 1917–1918 leg.; outer reef; SMNH 180478. • 1 specimen 65/50 mm; Gilbert Islands; Oct 1917; S Bock’s Pacific Expedition 1917–1918 leg.; outer reef; SMNH 180475. • 1 specimen 80/65 mm; Gilbert Islands, Apamama [Abemama]; 00°24'N, 173°55'E; 1917; S Bock’s Pacific Expedition 1917–1918 leg.; entrance reef; SMNH 180380. • 1 specimen 45/35 mm; Gilbert Islands, Apamama [Abemama]; 00N, 173E; 1917; S Bock’s Pacific Expedition 1917–1918 leg.; at low tide; SMNH 180379.

Madagascar • 1 specimen 65/50 mm; Tulear [Toliara]; 23°22'S, 43°39'E; Feb 1913; K Afzelius leg.; coral reef; SMNH 180381.

Maldive Islands • 1 specimen 85/55 mm; Tiladummati Atoll, Faro Islet, on reef NW of Fildau Island; 06°55.333'S, 73°11.833'E; 30 & 31 Mar 1964; R Robertson, International Indian Ocean Expedition leg.; st R021, intertidal, on dead coral rubble; ANSP 304860.

Marshall Islands • 1 specimen 37/30 mm; Jaluit; 06N, 170E; 20 Oct 1917; C Hessle, S Bock’s Pacific Expedition 1917–1918 leg.; west shore southeast of entrance; SMNH 180356.

Mauritius • 10 specimens up to 90/60 mm; probably Mauritius according to a new label (the original label was destroyed); 1929–1930; T Mortensen leg.; NHMD 613752.

New Caledonia • 1 specimen 100/60 mm; Touho, NW, Koë Reef, 2 mi. SSE; 16–20 Jan 1961; Kline & Orr leg.; 0–4 feet, live and dead coral, sand, weed; ANSP 270221.

Palau • 1 specimen 80/65 mm; ANSP 203028.

Seychelles • 1 specimen 90/70 mm; 1830; Dussumier leg.; MNHN-IM-2012-25149. • 1 specimen 85/60 mm; 1841; L. Rousseau leg.; MNHN-IM-2012-25148.

Tanzania • 1 specimen 65/50 mm; Zanzibar; 1902; C Eliot leg.; ANSP 84336. • 1 specimen 80/65 mm; west coast; Jun 1995; M Richmond & M Toni (from N Yonow’s personal collection) leg.; sheltered, on limestone rock, intertidal exposed at low tide, common at night; MNHN-IM-2014-7991.

GenBank sequence

One COI sequence was obtained from GenBank (LC390402) for an individual identified as Peronia sp. and collected from Okinawa, Japan (Takagi et al. 2019), which is the northernmost confirmed locality for Peronia peronii.

Distribution

(Fig. 6). Given that our fresh molecular samples of P. peronii from the West Pacific (Guam, Papua New Guinea) are conspecific with those from Mauritius, it is assumed here that all individuals with a long spine of the accessory penial gland belong to the same species. Strictly speaking, however, the presence of P. peronii from places like Zanzibar, the Maldives, Nicobar Islands, West Papua, Timor, Palau, New Caledonia, and Tonga, would still need to be validated with fresh material.

Interestingly, but for unclear reasons, Peronia peronii seems to be only recorded from relatively small islands, the largest ones being Timor, New Caledonia, and Fiji. Even in Papua New Guinea, it was found on small islands close to the mainland but not on the mainland. Peronia peronii seems to be transported across vast distances from the western Pacific Ocean to the western Indian Ocean, but which does not seem to settle on the coasts of large land masses. We did not find it in any of the many localities we visited in the Philippines, Vietnam, Malaysia, Borneo, Sulawesi, Halmahera, Sumatra, etc. It is possible that we occasionally missed it in a few places (obviously we missed it in Timor and New Caledonia where it is present), but it is unlikely that we missed it everywhere.

The presence of P. peronii is confirmed in the following locations (Fig. 6): Chagos Archipelago (new record); Fiji (type locality of O. melanopneumon and P. fidjiensis; Hoffmann, 1928; present study); India, Nicobar Islands (Mörch 1872a, b: 325, as P. verruculata; Bergh, 1884a, as O. tonganum; Hoffmann, 1928; present study); Indonesia, Java (Hoffmann 1928; present study), Sumatra (Hoffmann 1928; Labbé 1934a; present study), Tanimbar (new record), Timor (Cuvier 1804, paralectotype of O. peronii), West Papua (type locality of O. punctatum Quoy & Gaimard, 1832); Japan, Okinawa (Takagi et al. 2019, as onchidiids of “Group II”; new record); Kiribati, Gilbert Islands (Hoffmann 1928; present study); Madagascar (Odhner 1919; present study); Maldive Islands (Marcus and Marcus 1960, 1970; present study); Mariana Islands, Guam (Dayrat et al. 2011; White et al. 2011; present study); Marshall Islands (Hoffmann 1928; present study); Mauritius (type locality of O. peronii and P. mauritiana; Semper 1880; Bergh 1884a, as O. tonganum; Plate 1893; present study); New Caledonia (new record); Palau (new record); Papua New Guinea, Madang (new record), New Ireland (new record); Seychelles (Labbé 1934a; present study); Tanzania, Zanzibar (new record); and Tonga (type locality of O. tonganum Quoy & Gaimard, 1832). The most western records of P. peronii are Zanzibar and southwestern Madagascar; its most eastern records are Okinawa, Guam, Kiribati, and Tonga. Note that P. peronii is most likely also present in Tokara Islands (Baba 1958: 144, as O. verruculatum), just south Kyushu, ca. 30N, which would be its most northern record.

The following records from the literature are not confirmed here, because authors did not provide enough information supporting the identification: Djibouti (Vayssière 1912; O’Donoghue 1929; Labbé 1934a); India, Nicobar (Godwin-Austen 1895, as O. mauritianum; Patil & Kulkarni, 2013); Indonesia, West Papua (Quoy and Gaimard 1832, as O. tonganum); Japan (Arimoto et al. 1993); Kenya (Martens 1897); Madagascar (Marcus and Marcus 1970); Mariana Islands, Guam (Biskupiak and Ireland 1985); Mozambique (Martens 1879; Connolly 1912, 1939; Macnae and Kalk 1958); Papua New Guinea, New Ireland (Labbé 1934a, as P. tongana); Persian Gulf (White 1951; Bitaab et al. 2015); Philippines (Casto de Elera 1896, as O. tonganum), Bohol (Semper 1880, as O. tonganum); Red Sea (Sturany 1904); Samoa (Semper 1880, as O. tonganum); South Africa, Natal (Krauss 1848; Sturany 1898; Collinge 1910; Connolly 1912, 1939; Morrisey et al. 2010); Australia, Lord Howe Island (Bretnall 1919; Hoffmann 1928), Torres Strait (Smith 1884, as Onchidium punctatum), Western Australia (Bretnall 1919).

Etymology

Onchidium peronii was named after François Péron [1775–1810] who collected the two slugs described by Cuvier during the Baudin expedition [1800–1803]. Peronia mauritiana, Onchidium tonganum, and Paraperonia fidjiensis were named after type localities. Onchidium punctatum was named after the speckled (punctatum in Latin) dorsal notum of live animals. Onchidium melanopneumon was named after the black (melas in Greek) lung (pneumon in Greek) tissue of the holotype.

Habitat

(Fig. 7). Live slugs of Peronia peronii are found in the rocky intertidal, like most other Peronia slugs. Many of our specimens were collected at night or just before sunrise, suggesting that P. peronii is, at least partly, a nocturnal species. This could explain why we missed it at some localities where we only collected during the day. Peronia peronii is not rare, but it is definitely not as common as some other species. The fact that collecting it at night seems necessary, at least in some localities, might explain why collections of P. peronii are not as abundant as collections of P. verruculata.

Figure 7. 

Habitat, Peronia peronii, Papua New Guinea, Madang, limestone rocky intertidal (st PM 12).

Color and morphology of live animals

(Fig. 8). No picture of live animals was available for individuals from the West Pacific (Guam and Papua New Guinea). The description of the color of live animals is based on the Mauritius individuals. The dorsal notum is brown, with a greenish hue, light to dark, mottled with darker and lighter areas. The color of the dorsal papillae varies a s that of the background itself. The ventral surface (foot and hyponotum) is yellowish-greenish and can change rapidly in any given individual. The ocular tentacles are brown-grey, like the head. The dorsal notum of live animals is covered by dozens of papillae of various sizes. Dorsal papillae can be particularly tall (easily up to 4 mm), even in preserved specimens, and are evenly distributed over the entire notum. Preserved, they are difficult to distinguish from retracted dorsal gills in the posterior half of the notum. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (15–20). The longest animals are 140 mm long in Mauritius and 115 mm long in the West Pacific.

Figure 8. 

Live animals, Peronia peronii, Mauritius A dorsal view, 140 mm long [5872] (MNHN-IM-2019-1605) B dorsal view, 125 mm long [5874] (MNHN-IM-2019-1605) C ventral view, same as A; D ventral view, same as B.

Digestive system

(Figs 912). Examples of radular formulae are presented in Table 5. The median cusp of the rachidian teeth is approximately 75 μm long. The hook of the lateral teeth is approximately 160–200 μm long. The intestinal loops are of type I, with a transitional loop oriented between 12 to 3 o’clock.

Figure 9. 

Digestive system, dorsal view, Peronia peronii, type specimens. The arrow indicates the orientation of the transitional loop A paralectotype, Onchidium peronii, Timor (MNHN-IM-2000-22938) B lectotype, Onchidium tonganum, Tonga (MNHN-IM-2000-22937) C lectotype, Onchidium punctatum, Indonesia, West Papua (MNHN-IM-2000-22966) D possible paralectotype, Paraperonia gondwanae, Mauritius (MNHN-IM-2000-33686) E lectotype, Paraperonia fidjiensis, Fiji (MNHN-IM-2000-33692). Scale bars: 5 mm (A, D), 10 mm (B, C, E). Abbreviations: ddg dorsal digestive gland, i intestine, pdg posterior digestive gland, st stomach.

Figure 10. 

Digestive system, dorsal view, Peronia peronii. The arrow indicates the orientation of the transitional loop A Mauritius [5874] (MNHN-IM-2019-1605) B Papua New Guinea, Madang [5472] (MNHN-IM-2013-14052) C Guam [5840] (MNHN-IM-2019-1609). Scale bars: 10 mm (A–C). Abbreviations: ddg dorsal digestive gland, i intestine, pdg posterior digestive gland, st stomach.

Figure 11. 

Radula, Peronia peronii A–C Papua New Guinea [5476] (MNHN-IM-2013-16260) D–H Guam [5840] (MNHN-IM-2019-1609) A lateral teeth B rachidian and innermost lateral teeth C rachidian and innermost lateral teeth D rachidian and innermost lateral teeth E rachidian and lateral teeth F lateral teeth G lateral teeth, frontal view H outermost lateral teeth. Scale bars: 100 μm (A), 40 μm (B, D), 80 μm (C), 200 μm (E, F), 100 μm (G, H).

Figure 12. 

Radula, Peronia peronii, Mauritius [5872] (MNHN-IM-2019-1605) A rachidian and innermost lateral teeth B rachidian and lateral teeth C outermost lateral teeth D lateral teeth. Scale bars: 40 μm (A), 100 μm (B), 20 μm (C), 200 μm (D).

Table 5.

Radular formulae in Peronia species. Each formula follows the same format: number of rows × number of lateral teeth per left half row - 1 (rachidian tooth) - number of lateral teeth per right half row. Each DNA extraction number corresponds to one individual. The letter H next to an extraction number indicates a holotype.

Species Radular formula Spm length (mm) - Locality DNA extraction number
P. verruculata (unit #1) 63 × 70-1-70 45 UMIZ 00170 Sulawesi 2127
73 × 92-1-92 40 ITBZC IM 00021 Vietnam 5621
56 × 60-1-60 25 MTQ Queensland 2622
74 × 75-1-75 45 UMIZ 00166 Halmahera 5068
52 × 57-1-57 40 UMIZ 00162 Ambon 2729
60 × 60-1-60 40 UMIZ 00168 Lombok 2987
70 × 72-1-72 50 UMIZ 00169 Seram 2870
70 × 75-1-75 35 MNHN-IM-2013-12010 Papua New Guinea 5469
56 × 56-1-56 17 MNHN-IM-2013-62393 Vanuatu 5481
P. verruculata (unit #2) 70 × 75-1-75 50 UMIZ 00178 Sumatra 1746
70 × 78-1-78 50 UMIZ 00180 Sumatra 1797
60 × 68-1-68 45 UMIZ 00180 Sumatra 1795
64 × 70-1-70 55 UMIZ 00180 Sumatra 1796
P. verruculata (unit #3) 68 × 78-1-78 35 USMMC 00051 Peninsular Malaysia 976
70 × 92-1-92 40 USMMC 00065 Peninsular Malaysia 2547
65 × 85-1-85 25 ZRC.MOL.10496 Singapore 990
72 × 86-1-86 35 USMMC 00064 Peninsular Malaysia 975
P. verruculata (unit #4) 73 × 85-1-85 50 MNHN-IM-2019-1384 Pakistan 6164
75 × 95-1-95 50 MNHN-IM-2019-1385 Pakistan 6165
75 × 92-1-92 40 MNHN-IM-2019-1386 Pakistan 6166
P. verruculata (unit #5) 65 × 75-1-75 40 MNHN-IM-2019-1610 Madagascar 3231
55 × 63-1-63 35 MNHN-IM-2019-1611 Madagascar 3144
55 × 65-1-65 25 MNHN-IM-2013-62398 Mozambique 5510
P. verruculata (Red Sea) 66 × 86-1-86 35 ZMH 27472 Red Sea #1
80 × 95-1-95 40 ZMH 27472 Red Sea #2
67 × 80-1-80 35 ZMH 27472 Red Sea #3
70 × 80-1-80 35 ZMH 27472 Red Sea #4
P. madagascariensis 85 × 90-1-90 40 MNHN-IM-2009-16392 Madagascar 5501
78 × 90-1-90 40 MNHN-IM-2009-16412 Madagascar 5504
47 × 50-1-50 10 UF 332088 Oman 703
70 × 72-1-72 35 NMSA W7547 South Africa 5841
P. peronii 90 × 115-1-115 110 MNHN-IM-2019-1606 Mauritius 3605
90 × 105-1-105 140 MNHN-IM-2019-1605 Mauritius 5872
95 × 105-1-105 80 MNHN-IM-2013-14052 Papua New Guinea 5472
90 × 100-1-100 70 MNHN-IM-2013-16260 Papua New Guinea 5476
100 × 110-1-110 85 MNHN-IM-2019-1609 Guam 5840
P. platei 75 × 75-1-75 12 UF 303653 Hawaii 706
65 × 78-1-78 12 UF 303653 Hawaii 5380
70 × 90-1-90 30 BPBM 284527 Hawaii 6160
70 × 80-1-80 30 BPBM 284528 Hawaii 6161
67 × 75-1-75 14 MNHN-IM-2013-13762 Papua New Guinea 5405
70 × 72-1-72 20 MNHN-IM-2013-13351 Papua New Guinea 5412
P. sydneyensis 56 × 60-1-60 30 AM C468916.001 New South Wales 1516 H
51 × 60-1-60 23 AM C468915.001 New South Wales 1517
47 × 45-1-45 6 MTQ Queensland 2667
58 × 70-1-70 50 MTQ Queensland 2680
35 × 35-1-35 12 MNHN-IM-2019-1594 New Caledonia 6189
55 × 70-1-70 41 MNHN-IM-2019-1595 New Caledonia 6195
45 × 46-1-46 25 MNHN-IM-2019-1598 New Caledonia 6220
P. okinawensis 60 × 60-1-60 20 UF 352288 Okinawa, Japan 696-2
60 × 60-1-60 25 UF 352288 Okinawa, Japan 696-3
65 × 65-1-65 27 UF 352288 Okinawa, Japan 696-4 H
P. setoensis 50 × 50-1-50 20 NSMT-Mo 78985 Wakayama, Japan 5383 H
55 × 55-1-55 15 NSMT-Mo 78987 Wakayama, Japan 3753
50 × 50-1-50 15 NSMT-Mo 78987 Wakayama, Japan 3754
P. griffithsi 50 × 45-1-45 18 UMIZ 00177 Kei 2934
50 × 50-1-50 17 UMIZ 00176 Kei 2936
50 × 45-1-45 25 UMIZ 00177 Kei 3566
45 × 52-1-52 20 MNHN-IM-2019-1608 Mauritius 3153
50 × 52-1-52 20 MNHN-IM-2019-1608 Mauritius 3156
50 × 50-1-50 15 MNHN-IM-2000-35265 Mauritius 3157 H
P. willani 58 × 80-1-80 50 NTM P.57625 Northern Territory 1628 H
53 × 60-1-60 40 NTM P.57627 Northern Territory 1668
65 × 80-1-80 60 NTM P.57627 Northern Territory 1626
70 × 90-1-90 65 NTM P.57626 Northern Territory 1620

Reproductive system

(Figs 1316). In the anterior (male) parts, the muscular sac of the accessory penial gland is at least 30 mm long in specimens from Mauritius and at least 25 mm long in specimens from the West Pacific (Guam & Papua New Guinea). Note that, in some additional museum specimens, the muscular sac was only 20 mm long, and, even exceptionally 17 mm long (see remarks below). The hollow spine of the accessory penial gland is narrow, elongated, and straight or slightly curved, and its shape (including at its tip) varies between individuals. Its length ranges from 3.4 mm ([5872] MNHN-IM-2019-1605) to 3.6 mm ([3605] MNHN-IM-2019-1606) in Mauritius, and from 3.5 mm ([5472] MNHN-IM-2013-14052) to 4 mm ([5471] MNHN-IM-2013-12500) in the West Pacific (Guam and Papua New Guinea). Its diameter at the conical base is approximately 400 μm in specimens from Mauritius and between 400 and 500 μm in specimens from the West Pacific (Guam and Papua New Guinea). Its diameter at the tip measures 160–170 μm in specimens from the West Pacific, and from 180 to 200 μm in specimens from Mauritius. Note that, in some additional museum specimens, the spine was only 3 mm long (see remarks below).

Figure 13. 

Posterior, hermaphroditic (female) reproductive system, Peronia peronii A Mauritius [3605] (MNHN-IM-2019-1606) B Papua New Guinea, Madang [5472] (MNHN-IM-2013-14052). Scale bars: 10 mm (A), 5 mm (B). Abbreviations: dd deferent duct, fgm female gland mass, hg hermaphroditic gland, ov oviduct, rs receptaculum seminis, sp spermatheca.

Figure 14. 

Anterior, male, copulatory apparatus, Peronia peronii A Mauritius [3605] (MNHN-IM-2019-1606) B Papua New Guinea, Madang [5472] (MNHN-IM-2013-14052). Scale bars: 10 mm (A), 5 mm (B). Abbreviations: ag accessory penial gland, dd deferent duct, ms muscular sac, ps penial sheath, rm retractor muscle, v vestibule.

The retractor muscle is shorter or longer than the penial sheath and inserts near the heart. Exceptionally, the retractor muscle can even be vestigial ([5472] MNHN-IM-2013-14052). Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 50 μm long.

Diagnostic features

(Table 4). Peronia peronii is the only Peronia species which is easy to identify anatomically. Indeed, it is characterized by a very long spine (at least 3 mm) of the accessory penial gland, which is distinctive and easily accessible (one just needs to pull on the flagellum of the penial gland or, even, in some cases, measure the spine by transparency). The two longest spines were found in the lectotype of P. fidjiensis (MNHN-IM-2000-33692) from Fiji (5 mm), and in an old historical specimen (ANSP 304860) from the Maldives (4.8 mm).

Peronia peronii is additionally characterized by a unique combination of anatomical traits: muscular sac longer than 20 mm, intestinal loops of type I (with a transitional loop oriented between 12 and 3 o’clock), retractor muscle inserting near the heart. Also, no individual larger than 80 mm was found in any other Peronia species so far. Animal size can be useful when several Peronia species are found at the same site. For instance, the two individuals of P. verruculata (unit #1) found at the station PM 12 (near Madang, Papua New Guinea) are 35 and 38 mm long while the individual of P. peronii from the same station is 80 mm long. The type I of its intestinal loops (with a transitional loop oriented between 12 and 3 o’clock) is only shared by P. okinawensis, a species endemic to Japan with which it is most closely related.

Figure 15. 

Penial hooks, Peronia peronii A Mauritius [5872] (MNHN-IM-2019-1605) B Mauritius [3605] (MNHN-IM-2019-1606) C, D Guam [5840] (MNHN-IM-2019-1609). Scale bars: 6 μm (A, B, D), 40 μm (C).

Figure 16. 

Accessory penial gland spine, Peronia peronii A, B, F, G Mauritius C, D, H Papua New Guinea E, I Guam A [3605] (MNHN-IM-2019-1606) B [5872] (MNHN-IM-2019-1605) C [5471] (MNHN-IM-2013-12500) D [5472] (MNHN-IM-2013-14052) E [5840] (MNHN-IM-2019-1609) F same as A; G same as B; H same as C; I same as E. Scale bars: 800 μm (A–D), 1 mm (E), 40 μm (F–I).

Remarks

Synonymies. There is no doubt that Cuvier’s (1804) Onchidium peronii applies to the species described here, just based on animal size alone. According to Cuvier, the lectotype from Mauritius measured approximately 140 mm long and our molecular data show that all individuals of that size from Mauritius belong to a single species (Table 4). Cuvier’s (1804: pl. 6) detailed anatomical description and drawings are exclusively based on the lectotype (he did not dissect the paralectotype from Timor). Cuvier (1804: 48, pl. 6, fig. 8) described the spine of the accessory penial gland as a “very sharp, brown spike” but unfortunately did not provide its length. However, Cuvier’s (1804: pl. 6, fig. 4) illustration of the intestinal loops is identical to some of our Mauritius individuals here: intestinal loops of type I with a transitional loop at 3 o’clock. The paralectotype of Onchidium peronii from Timor (MNHN-IM-2000- 22938) is only briefly mentioned by Cuvier in the original description. The length (4.5 mm) of the spine of its accessory penial gland (checked for the present study) indicates that it also belongs to P. peronii. Its intestinal loops are also identical to those of the lectotype (Fig. 9A).

Peronia mauritiana is a junior objective synonym of Onchidium peronii because they share the same name-bearing type.

Onchidium tonganum was described by Quoy and Gaimard (1832: 210–211, pl. 15, figs 17, 18) from “Panhi-Motou,” possibly the small island of Pangaimotu, Tonga, based on an unspecified number of individuals. The illustrations of the dorsal gills by Quoy and Gaimard (1832: pl. 15, figs 17, 18) and their presence on the notum of the lectotype (MNHN-IM-2000-22937) clearly indicate that Onchidium tonganum belongs to Peronia. The lectotype was dissected prior to the present study and most of the male copulatory parts are missing (only the deferent duct remains). As a result, the length of the spine of the accessory penial gland, which is diagnostic of P. peronii, cannot be checked. Labbé (1934a: 191) listed the lectotype in the material he examined for his re-description of P. tongana, but he did not point out that it was part of the type material of O. tonganum and he did not describe it anatomically. It is possible but not certain that Labbé dissected the lectotype. At any rate, its intestinal loops are of type I with a transitional loop between 2 and 3 o’clock (Fig. 9B). Both the length (100 mm) of the lectotype as well as its intestinal loops indicate that Peronia tongana is a junior synonym of P. peronii (Table 4).

Onchidium punctatum is regarded here as a junior synonym of P. peronii because the length (3.7 mm) of the spine of the accessory penial gland of the lectotype (MNHN-IM-2000-22966) is only compatible with P. peronii (Table 4). The length of the lectotype (70 mm, preserved) is also far more compatible with P. peronii than with P. verruculata, another species found in West Papua. Our many individuals of P. verruculata are all less than 60 mm long (alive), except a single individual from New Caledonia (73 mm alive). Given their small size, the two paralectotypes (MNHN-IM-2000-33701) likely belong to P. verruculata (unit #1) instead of P. peronii, which would not be surprising at all because the type locality of O. ferrugineum (a junior synonym of P. verruculata) is the same as that of O. punctatum (Manokwari, West Papua, Indonesia). At the end of the description of O. punctatum, Quoy & Gaimard (1832: 216) also mention in passing that they also found Onchidium tonganum in Port Dorey (i.e., Manokwari, West Papua, Indonesia) and they even point out that local inhabitants know how to distinguish both species. Both O. punctatum and O. tonganum are regarded here as junior synonyms of P. peronii. However, it remains true that there are two sympatric Peronia species in West Papua, P. verruculata and P. peronii, which can be distinguished in the field based on animal length (except, of course, for individuals measuring less than 60 mm long).

Bergh (1884a: 129–142, pl. IV, figs 25–27, pl. V, figs 1–27, pl. VI, figs 5–18, 20, 21) described Onchidium melanopneumon from a single individual (65/40 mm) from Fiji. This specimen was completely dissected by Bergh and is now empty (NHMUK 1888.5.30.39). Onchidium melanopneumon applies to a Peronia species due to the presence of dorsal gills, and the length (4 mm) of the spine of the accessory penial gland indicates that it applies to P. peronii (Table 4). Its intestinal loops (Bergh 1884a: pl. V, fig. 27) are also similar to those found in P. peronii, although the transitional loop is slightly past the 3 o’clock limit. As a result, O. melanopneumon is regarded as a junior synonym of P. peronii. Bergh (1884b: 263; 1885: 176) briefly mentioned again O. melanopneumon in a comparative study on the affinities of onchidiids.

Labbé (1934a: 197–198, figs 9–11) described Paraperonia fidjiensis based on seven individuals from Fiji, one of which could be found and is designated as the lectotype (MNHN-IM-2000-33692). Because all reproductive parts are missing, the length of the spine of the accessory penial gland cannot be checked. However, according to Labbé (1934a: 197, fig. 10), the spine of the accessory penial gland is 5 mm long, which is only compatible with P. peronii (Table 4), and is the longest spine known in P. peronii. The intestinal loops of the lectotype of P. fidjiensis are clearly of type I, with a transitional loop oriented at ~ 1 o’clock (Fig. 9E), even though Labbé (1934a: 197) erroneously described them a type V, which is a mistake he often made. Given the length of the lectotype (60 mm) and, most importantly, the length of the spine of the accessory penial gland, P. fidjiensis is regarded as a junior synonym of P. peronii.

Secondary literature. Several early authors mentioned Cuvier’s Onchidium peronii without any new material (Cuvier 1816: 411; Cuvier 1830: 46; Férussac 1822: xxxi; Fleming 1822a: 574; Fleming 1822b: 463; Lamarck 1822: 46; Voigt 1834: 101). Oken (1834a: 287) transferred Quoy and Gaimard’s (1832) Onchidium tonganum and O. punctatum to Peronia but with no justification.

In the seventh volume of the second edition of Lamarck’s Histoire naturelle des animaux sans vertèbres, which was revised by Deshayes and Milne-Edwards (1836), P. mauritiana is proposed as a synonym of Onchidium peronii. However, as a reference for P. mauritiana, the authors mentioned the illustration published by Blainville (1827: pl. 46, fig. 7) in the Atlas of his Manuel which differs from that published by Cuvier (1804: pl. 6, fig. 1) and may or may not refer to Peronia mauritiana.

John Edward Gray (1850: 117) listed Onchidium peronii as a synonym of P. mauritiana and his wife Maria Emma Gray (1850: pl. 181, fig. 7) reproduced Cuvier’s (1804: pl. 6, fig. 1) original figure of the dorsal notum of Onchidium peronii. As a result, JE Gray (1850: 117) and ME Gray (1850: pl. 181, fig. 7) are listed above as correct references of O. peronii. In the same work, JE Gray (1850: 117) regarded P. punctata and P. tongana (as spelling mistake tongensis) as valid, and ME Gray (1850: pl. 182, fig. 1, pl. 183, fig. 3) reproduced the original illustrations by Quoy and Gaimard (1832: pl. 15, figs 17, 18, 27, 28). As a result, those names are also listed above as correct references. According to JE Gray (1850: 117), P. mauritiana (as mauriciana) was a valid Peronia species name but ME Gray (1850: pl. 183, fig. 2) reproduced Blainville’s (1827: pl. 46, fig. 7) illustration which differs from that published by Cuvier (1804: pl. 6, fig. 1) and which may or may not refer to P. peronii because there are two Peronia species in Mauritius (Fig. 6). Therefore, ME Gray’s (1850: pl. 183, fig. 2) Peronia mauritiana is not listed above as a correct reference of P. peronii. And, finally, ME Gray’s (1850: pl. 183, figs 4, 4a, 5) reproductions of Savigny’s (1817: pl. II, figs 3.1–3.3) illustrations of Onchidium peronii from the Red Sea do not represent P. peronii (see remarks on P. verruculata).

Adams and Adams (1855: 235) merely listed Peronia mauritiana, P. peronii, P. punctata, and P. tongana as Peronia species names. Note that for P. peronii, they refer to Savigny’s illustrations of individuals from the Red Sea misidentified as P. peronii by Audouin instead of Cuvier’s original description of P. peronii, which means that Adams and Adams refer to P. verruculata instead of P. peronii (see remarks on P. verruculata). Adams and Adams (1855: pl. LXXXI, fig. 3) also reproduced the original illustration of O. tonganum by Quoy and Gaimard (1832: pl. 15, fig. 17).

Berge (1855: 124) mentioned “Onchidium peronii Cuv.” from the East Indies and the Red Sea but with no new material or literature reference except for a German translation of Cuvier’s Règne Animal by Voigt (1834: 101) as well as “Cuvier, Règ. anim. pl. 26, fig. 2.” Berge (1855: 124) followed Voigt (1834: 101) and accepted P. mauritiana as a synonym of O. peronii. Cuvier’s illustration (pl. 26, fig. 2) mentioned by Berge was actually published after Cuvier’s death in the Disciples’ edition of the Règne Animal which was accompanied by beautiful illustrations. According to Cowan (1976), the authorship for the mollusks should be attributed to Deshayes (1836–1845) who prepared the volume of text and the atlas published in livraisons between 1836 and 1845. However, the exact dates of publication are still unknown for most pages and plates, including for the page 69 and the plate 26 where Onchidium is mentioned and illustrated. Note the spelling mistake Unchidium on the figure caption of plate 26. The illustrations in both Deshayes (1836–1845: pl. 26, fig. 2) and Berge (1855: pl. 16, fig. 8) are mere reproductions of Cuvier’s (1804: pl. 6, fig. 5) anatomical drawing of O. peronii. Berge (1855: 124) also mentioned “Onchidium punctatum Quoy” from Australia (as Neuholland) but with no new material or literature reference except for another illustration (pl. 26, fig.1) from the Disciples’ edition of the Règne Animal. Again, the illustrations in both Deshayes (1836–1845: pl. 26, fig. 1) and Berge (1855: pl. 21, fig. 7) are mere reproductions of Quoy and Gaimard’s (1832: pl. 15, fig. 27) original illustration of O. punctatum. It cannot be determined which species Berge referred to exactly (because the localities mentioned by Berge are not the type localities).

The record of Onchidium peronii from Natal, South Africa (Krauss 1848: 72) likely is a record of P. madagascariensis, the only Peronia species known in South Africa so far (see remarks on P. madagascariensis). However, P. verruculata (unit #5) could also be present in northeastern South Africa because its southernmost known locality is in Maputo, Mozambique (ca. 26°S). This record by Krauss was mentioned again by a few authors (Sturany 1898: 73; Collinge 1910: 171; Connolly 1912: 224–225; Connolly 1939: 454).

Chenu (1859: 474, fig. 3505) mentioned Peronia punctata with no additional material or records, and with a reference to Quoy and Gaimard’s (1832: pl. 15, fig. 27) original illustration of O. punctatum.

Keferstein (1865a: pl. CII, fig. 20) reproduced Quoy and Gaimard’s (1832: pl. 15, fig. 17) original illustration of Onchidium tonganum, which he classified in Peronia. Keferstein (1865a: pl. CIII, fig. 1) also reproduced Cuvier’s (1804: pl. 6, fig. 4) original illustration of the internal anatomy of O. peronii, which he also classified in Peronia.

Based on the collections of the Galathea Expedition preserved in Copenhagen, Mörch (1872a: 28; 1872b: 325) mentioned Peronia verruculata (as spelling mistake vermiculata in 1872b) from Pulo Milu [Pulo Milo, Little Nicobar] and Nancouri [Nancowry, Nicobar Islands], where he says it is common. Given the animal size (up to 133 mm long alive), we agree with Hoffmann (1928: 71) that Mörch’s record is very likely a record of P. peronii. The preserved specimen (88/38 mm) reported by Mörch (1872a: 28; 1872b: 325) from the Galathea collections most likely is the specimen identified by Semper as Onchidium tonganum, described by Bergh (1884a: 142–148, pl. VI, fig. 19, pl. VII, figs 1–6), examined by Hoffmann (1928: 44) for his description of O. peronii, and finally re-examined for the present study (NHMD 613753). Bergh (1884b: 264; 1885: 177) briefly mentioned O. tonganum again in a comparative study on the affinities of onchidiids. Mörch (1872a: 28; 1872b: 325) mentioned Peronia mauritiana from Sambelong, Great Nicobar, Nicobar Islands, based on much smaller individuals from the collections of the Galathea Expedition in Copenhagen, which are a record for Peronia verruculata (see remarks on that species).

The record of Onchidium mauritianum from the Red Sea by Pagenstecher (1877: 62) refers to either Peronia verruculata or P. madagascariensis (Fig. 6).

The records of Onchidium peronii from Mozambique by Martens (1879: 735) in Ibo Island (ca. 12°21'S) and Inhambane (ca. 23°52'S) are within the geographical range of both P. verruculata (unit #5) and P. madagascariensis (Fig. 6). It is not possible to know to what species Martens was referring; this record by Martens was mentioned twice by Connolly (1912: 225; 1939: 454).

Semper (1880: 258–260, pl. XIX, figs 2, 9, pl. XXII, figs 1, 2, 10) referred to huge onchidiid slugs (from 50 to 105 mm, preserved) as Quoy and Gaimard’s (1832) Onchidium tonganum and merely suggested, with a question mark, that O. peronii could refer to the same species. Semper (1880: 258) listed five geographical records for O. tonganum: Tonga and West Papua (as Port Dorey), from Quoy and Gaimard (1832); Mauritius, based on some material from the Vienna and Kiel museums; Samoa, based on some material from the Museum Godeffroy; and Bohol, Philippines, based on his own collections. Semper (1880: 258) indicated that the specimens he examined were from 50 to 105 mm long, preserved, and that the smallest individual was found in Mauritius. His anatomical description perfectly matches the anatomy of P. peronii. In particular, a spine of an accessory penial gland measuring 4 mm long is only compatible with P. peronii (Table 4). However, he did not clearly indicate whether he observed a long spine in every specimen. It cannot be excluded that he measured the length of the accessory penial gland spine only in a specimen from Mauritius. Therefore, the records of P. peronii in Bohol and in Samoa are regarded here as questionable, even though it is very possible that P. peronii lives in Samoa, given that it is so close to Tonga (800 km) and Fiji (1100 km).

Semper (1882: 290) thought that Cuvier’s (1804) original description of P. peronii was problematic because his drawing of the dorsal notum did not match the internal anatomy. Because Semper was convinced that Cuvier used specimens that did not belong to the same species, he thought that the name P. peronii should not be used. Plate (1893: 172–173) disagreed with Semper even without examining the type material of P. peronii. It is demonstrated here that the two type specimens described by Cuvier as P. peronii both belong to the same species (see above). Semper (1882: 268) was undecided about the nomenclatural status of what he called Onchidium mauritianum (then a new combination), which he listed as one of the names for which a “closer inspection of the originals” was needed. Like most authors, he cited Blainville’s (1827: pl. 46, fig. 7) illustration (which is not part of Blainville’s original description) as a reference without realizing that it may or may not correspond to P. mauritiana, a junior objective synonym of P. peronii. Semper (1882: 289) was also undecided about the status of Onchidium punctatum, for which he erroneously thought that the type locality was unknown. He suggested that it might refer to the same species as Onchidium tumidum, which is not possible because O. tumidum was recently transferred to Paromoionchis (Dayrat et al. 2019a).

Tapparone Canefri (1883: 214) listed all of Semper’s geographic records for Peronia tongana with no new material or anatomical observations (see above). Tapparone Canefri (1883: 214) also regarded Peronia punctata as a valid species name, but with no other reference or material than the original description by Quoy and Gaimard (1832). Tapparone Canefri’s suggestion that Peronia punctata could refer to the same species as Onchidium tumidum must be rejected because O. tumidum was recently transferred to Paromoionchis (Dayrat et al. 2019a).

Smith (1884: 92) mentioned Onchidium (Peronia) punctatum from Albany Island and Thursday Island, in the Torres Strait, without any description. This is likely a record of Peronia verruculata (unit #1), the only species thought to be present in the Torres Strait, although our study does not include any fresh material from the Torres Strait and P. peronii could also live there (Fig. 6). Note that Thursday Island also happens to be the type locality of Scaphis viridis, a junior synonym of Peronia verruculata.

Bergh (1884a: 142–148, pl. VI, fig. 19, pl. VII, figs 1–6) described as Onchidium tonganum a specimen from the collections of the Copenhagen Museum which was collected in the Nicobar Islands during the Galathea Expedition (station 305). That specimen (85/55 mm), dissected by Bergh, is in a jar (NHMD 613753) with a second specimen (70/50 mm) which is still entire and not dissected by Bergh. Both specimens were re-examined for the present study, although Bergh’s measurement of the penial gland spine in the largest specimen (4.25 mm) could not be checked because internal organs are missing. Given the specimen sizes, their intestinal loops (type I with a transitional loop at 3 o’clock in the second specimen), and the spine of their accessory penial glands (4.25 mm in the largest specimen according to Bergh, and 4 mm in the second specimen), those two specimens belong to P. peronii.

Joyeux-Laffuie (1885: viii–xi) merely mentioned O. melanopneumon in a summary of Bergh’s (1884a) work.

Plate (1893: 172–173, pl. 12, figs 85, 87, 91) re-described Onchidium peronii based on at least one specimen from Mauritius for which he did not provide any size. However, given the length of the spine of the accessory penial gland (7 mm long), there is no doubt that he examined P. peronii. It is possible that he included a part of the duct of the accessory penial gland in that measurement because the longest spine observed in the present study was 5 mm, in the lectotype of P. fidjiensis (MNHN-IM-2000-33692). According to Plate, the retractor muscle inserts near the central nervous system, which does fit in the variation observed here (Table 4). Plate listed several synonyms: Peronia mauritiana, Onchidium tonganum, O. melanopneumon, and possibly (with a question mark) P. corpulenta. Note that Plate (1893: 172) rightly regarded O. melanopneumon as a junior synonym of O. peronii but for a weak reason (a similar pigmentation of the lung). These synonymies are all accepted here, except for P. corpulenta which is regarded as a nomen dubium (see general discussion). Plate (1893) did not comment on O. punctatum.

Godwin-Austen (1895: 443) listed Onchidium mauritianum in Little Nicobar. It is impossible to know what species was referred to. However, P. peronii (of which P mauritiana is a junior synonym), is known to be present in Nicobar Islands.

Casto de Elera (1896: 629) mentioned the presence of several species in the Philippines, without description or new material, mostly based on Semper’s (1880–1885) work: Onchidium verruculatum, O. tonganum, and O. savignyi (as savigngi). Our data suggest that Peronia verruculata (unit #1) lives in the Philippines (Fig. 6).

Martens (1897: 126) listed Peronia mauritiana as a synonym of Onchidium peronii with a reference to Blainville’s (1827: pl. 46, fig. 7) illustration of P. mauritiana which may or may not refer to P. mauritiana. Martens (1897: 126) also claimed that O. tonganum is a synonym of O. peronii, with a reference to the original description by Quoy and Gaimard (1832) as well as to Semper’s (1880: 258–260, pl. XIX, figs 2, 9, pl. XXII, figs 1, 2, 10) re-description, which may only partly correspond to P. peronii (see above). The record of O. peronii in Mombasa (Mombas, Ostküste Afrika) by Martens (1897: 126) is not supported by any description and is therefore not accepted here, even though it is possibly correct (P. peronii is present in Zanzibar).

Collinge (1900: 7) and Connolly (1912: 225) mentioned Onchidium peronii from Green Point, Cape Peninsula, South Africa. Those specimens were later used by Watson (1925: 283–284, pl. XXVII, figs 4–11, pl. XXVIII, figs 12, 14, pl. XXXI, fig. 58) to describe Onchidella capensis Watson, 1925.

Sturany (1904: 269) mentioned the presence of Onchidium peronii in Massawa, Eritrea, Red Sea. This record most likely refers to either Peronia verruculata or P. madagascariensis (Fig. 6).

Onchidium punctatum is one of the eight onchidiid species mentioned by Hedley (1909: 369) from Queensland, Australia, without any reference to any material. It is impossible to know what species Hedley refers to. Our data show that there are two Peronia species in Queensland (Fig. 6).

The record of Onchidium peronii from Durban, Natal, South Africa by Collinge (1910: 171) likely is a record of P. madagascariensis, the only Peronia species known in South Africa so far (see remarks on P. madagascariensis). However, P. verruculata (unit #5) could also be present in northeastern South Africa because its southernmost known locality is in Maputo, Mozambique (ca. 26°S). This record was mentioned again by Connolly (1912: 225; 1939: 454).

According to Connolly (1912: 224–225), Onchidium peronii is a valid name and Peronia mauritiana (as spelling mistake mauritziana) and O. tonganum are its synonyms. The references listed by Connolly are all commented on above. Let us briefly emphasize here, however, that the localities of Onchidium peronii mentioned by Connolly in South Africa and Mozambique are problematic. Connolly (1939: 454) later admitted that “it is open to question (...) whether the true O. peronii Cuv. really exists in South Africa.” Connolly (1939:453), who did not cite Labbé’s (1934a) work, considered that Peronia was a subgenus of Onchidium and should include onchidiid slugs with dorsal gills.

Vayssière (1912: 125–129) recorded seven individuals of Peronia peronii shipped to him from Moucha Islands (Djibouti) by Charles Gravier and Félix Pierre Jousseaume, two of the people who also collected many specimens studied by Labbé (1934a). Vayssière mostly focused on the description of the radula, which is not useful to identify species. Vayssière reported a wide range of animal sizes (from 10 to 80 mm long and from 6 to 60 mm wide). Thus, it is very possible that he examined more than one species. Instead of P. peronii, which has never been positively recorded from Djibouti, Vayssière likely examined P. verruculata, P. madagascariensis, or both (Fig. 6). His specimens of large size most likely were P. madagascariensis because P. verruculata individuals rarely are longer than 60 mm (Table 4). Note that the number of rows of teeth and the number of teeth per half row mentioned by Vayssière (95 to 100 rows on average) are higher than what was observed here, although they are more compatible with P. madagascariensis than P. verruculata (Table 5), acknowledging that radular formulae are expected to vary.

It is not possible to determine to what species Odhner (1919: 42) was referring solely based on his brief, external description of Onchidium peronii from Toliara, Madagascar. However, his material, dissected here, clearly belongs to P. peronii: a single individual (65/50 mm) is characterized by intestinal loops of type I with a transitional loop at 3 o’clock, a spine of the accessory penial gland of 3 mm long, and a muscular sac of 25 mm long (SMNH 180381).

Bretnall (1919) uncritically took for granted every species record ever published, without considering that species often are misidentified. Bretnall (1919) accepted O. peronii as a valid name, with Onchidium tonganum and Peronia mauritiana as synonyms, and P. corpulenta as a potential synonym (with a question mark). The references listed by Bretnall (1919: 311–312) for O. peronii are all commented on above already. However, Bretnall’s (1919: 313) list of geographic records needs to be discussed, especially because Bretnall did not mention the key characters supporting a proper identification of P. peronii (Table 4). The presence of P. peronii in Samoa, which Bretnall obtained from Semper (see above), should not be taken for granted, even if it is quite possible. The presence of P. peronii in the Buccaneer Archipelago, northern Western Australia (16S, 123E), based on specimens from the Australian Museum, should not be taken for granted, even though it is quite possible. The identification of P. peronii in the Santa Cruz Islands, Solomon Islands, based on specimens from the Australian Museum, should not be taken for granted (specimens may have been misidentified), even if the Santa Cruz Islands are within the known geographical range of P. peronii (Fig. 6). Bretnall (1919: 315–316) also regarded O. melanopneumon as a valid name, for which he cited Bergh’s (1884a) original description and its French summary by Joyeux-Laffuie’s (1885), and indicated Plate’s (1893) proposed synonymy (with O. peronii) with a question mark. Bretnall (1919: 316) listed Lord Howe Island, off southeastern Australia (based on specimens from the Australian Museum), as a locality for O. melanopneumon, but without description of key characters. Thus, the presence of P. peronii in Lord Howe Island, which is 1350 km south of the southernmost known locality of P. peronii (New Caledonia), is not taken for granted here. As for Onchidium punctatum, Bretnall (1919: 316–317) followed Semper (1882: 289) and Tapparone Canefri (1883: 214) who both thought that it could be a synonym of Onchidium tumidum (see above), which is not possible because O. tumidum refers to a Paromoionchis species (Dayrat et al. 2019a).

Hoffmann (1928: 71), following most of Plate’s (1893) nomenclatural decisions, accepted Peronia mauritiana, P. corpulenta, Onchidium tonganum and O. melanopneumon as junior synonyms of O. peronii. Hoffmann, like other authors, did not mention the key anatomical characters that allow a reliable identification of P. peronii and uncritically accepted most geographical records published before him. As a result, his proposed distribution for O. peronii should not be taken for granted. For instance, the presence of P. peronii in Lord Howe Island, off southeastern Australia, obtained from Bretnall (1919) is questionable. Hoffmann (1928: 44) examined a specimen from the Nicobar Islands (NHMD 613753) which was originally mentioned by Mörch (1872a: 28; 1872b: 325; see above). Hoffmann (1928: 44–45) also provided several geographical records (Sumatra, Java, Marshall Islands, Kiribati, Fiji) for O. peronii based on material preserved at the SMNH in Stockholm. His material was re-examined and all records are confirmed. Hoffmann only dissected two individuals, one from Sumatra (SMNH 180354) and one from Kiribati (SMNH 180379). The other eighteen specimens were dissected for the present study.

Eight large specimens (longer than 65 mm) examined by Hoffmann from Sumatra (SMNH 180354), Java (SMNH 180355), Kiribati (SMNH 180376, 180377, 180380, 180382, 180475), and Fiji (SMNH 180373) share the diagnostic characteristics of P. peronii: a spine of the accessory penial gland between 3 and 4 mm long, intestinal loops of type I with a transitional loop at 3 o’clock, and a muscular sac between 20 and 25 mm long (exceptionally 17 mm, SMNH 180354). Seven smaller specimens (between 15 and 37 mm long) examined by Hoffmann from the Marshall Islands (SMNH 180356), Fiji (SMNH 180374), and Kiribati (SMNH 180353, 180383, 180384) are immature: the anterior male reproductive parts are barely developed, and, if present, the spine of the accessory penial gland is still soft (SMNH 180353). Given their intestinal loops (type I with a transitional loop at 3 o’clock), they are regarded as individuals of P. peronii. In other species, individuals of that size are already fully mature. Two smaller specimens (between 28 and 37 mm long) examined by Hoffmann from Fiji (SMNH 180357, 180375) belong to P. peronii because of several characteristics (retractor muscle inserting near the heart, intestinal loops of type I with a transitional loop at 3 o’clock, a spine of 3 mm long). Their muscular sacs (11 and 15 mm) are shorter than in other specimens, suggesting that they likely are not fully mature. Two specimens from Kiribati (SMNH 180378, 180478), poorly preserved, could not be confidently identified. Finally, the male reproductive parts are missing in a specimen from Kiribati dissected by Hoffmann (SMNH 180379), but its intestinal loops (type I with a transitional loop oriented between 1 and 2 o’clock) confirm that it belongs to P. peronii.

Note that the locality of the specimen from Sumatra (SMNH 180354) is problematic. The label and Hoffmann’s publication both say “Pulu Pasu, west coast of Sumatra,” but there is no such place on the west coast of Sumatra. There are two small islands off the west coast of Sumatra called Pulau Asu (Hinako Islands) and Pulau Pasumpahan (south of Padang). There also is a small island called Pulau Pasu in the Riau Islands, but that archipelago is located north of Sumatra, in the South China Sea. So, it is unclear where that specimen was collected exactly in Sumatra.

O’Donoghue (1929: 833) reported one specimen (30/21 mm) of Peronia peronii from Port Taufiq, Suez, Egypt. A radular formula (65 × 72–1-72) is not enough to identify a Peronia species, and he most likely examined P. verruculata or P. madagascariensis (Fig. 6).

Two names accepted as valid by Labbé (1934a) are regarded as synonyms of Peronia peronii: P. tongana, and P. fidjiensis. Labbé (1934a: 191) himself acknowledged that differences between P. peronii and P. tongana were weak. The traits that he mentioned (position of the pneumostome with respect to the anus, head longer than the foot) vary greatly due to preservation. Labbé (1934a: 197–198) did not compare Paraperonia fidjiensis with Peronia peronii probably because he classified them in two distinct genera. However, there are no differences between the type material of P. fidjiensis and the type material of P. peronii. Labbé (1934a: 190) agreed with most authors that P. mauritiana and O. melanopneumon were synonyms of P. peronii. Like Plate (1893), Labbé (1934a: 190) thought that P. corpulenta was simply a potential synonym of P. peronii but in fact it is a nomen dubium (see general discussion).

All references cited by Labbé for P. peronii and P. tongana have been commented on above, but Labbé’s (1934a) proposed distribution ranges need additional clarification. Labbé’s (1934a: 190–191) re-description of P. peronii was based on one individual (100/70 mm) from Sumatra (MNHN-IM-2012-25150), one individual (90/70 mm) from the Seychelles (MNHN-IM-2012-25149), and ten individuals from the Red Sea (not found in the MNHN collections). At least one of those specimens belongs to P. peronii because of the length of the spine of the accessory penial gland mentioned by Labbé as 6 to 7 mm. The specimens from Sumatra and the Seychelles were fully dissected by Labbé (the Sumatra individual is basically empty): the male parts are missing, and it is not possible to determine the type of intestinal loops. However, given their huge size, they most likely belong to P. peronii. The presence of P. peronii in the Red Sea is possible but, at this stage, questionable: the size mentioned by Labbé for those specimens (17/12 mm) strongly suggests that he did not examine P. peronii from the Red Sea. Those specimens from the Red Sea identified as P. peronii by Labbé could not be located at the MNHN (there are no specimens collected by Clot-Bey in the collections, and there are too many jars of specimens collected by Jousseaume to determine which jar corresponds to the species description in Labbé’s monograph).

Labbé’s (1934a: 191–192, figs 4–7) re-description of P. tongana was based on one individual from Djibouti (Obock), one individual (85/60 mm) from the Seychelles (MNHN-IM-2012-25148), two individuals from New Ireland, and one individual from Tonga which happens to be part of the type series by Quoy and Gaimard (MNHN-IM-2000-22937) even though Labbé does not mention it. The specimen from the Seychelles was re-examined for the present study and, given its huge size, it is confirmed that it belongs to P. peronii: its intestinal loops are of type I, with a transitional loop at 3 o’clock; the male parts are missing. There are two specimens (60/50 mm) from New Ireland at the MNHN which could potentially be the two specimens mentioned by Labbé, but the collecting dates do not match. At any rate, it does not matter much since our fresh specimens demonstrate that P. peronii is present in New Ireland (Fig. 6). The specimen from Obock could not be traced back at the MNHN; there is a specimen (80/60 mm) which could possibly correspond to it but it is a problematic specimen as it could also be a type specimen for P. gaimardi, and is now an empty notum (see below, remarks on the type material of P. gaimardi in P. verruculata). Thus, the presence of P. peronii in Djibouti is not accepted here and would need to be supported by positive evidence.

Risbec (1935: 415) illustrated the eggs of an onchidiid individual from New Caledonia which he called “Oncidium tonga Q et G,” clearly a spelling mistake for Onchidium tonganum Quoy & Gaimard, 1832. It is not possible to know what species Risbec was referring to because there are three Peronia species in New Caledonia (Fig. 6).

White (1951: 241) reported a single specimen (53/38 mm) of Onchidium peronii from the Persian Gulf. The radular formula (88 × 88–1-88) is not enough to identify a Peronia species. White’s record referred either to P. verruculata (unit #4) or P. madagascariensis (Fig. 6).

In Japan, Baba (1958: 144) indicated that some specimens of Onchidium verruculatum from Tokara Islands, south of Kyushu (ca. 30°N) are very large (up to 120 mm long), suggesting that P. peronii is found there, which would be its most northern record.

Macnae and Kalk (1958: 34, 44, 128) mentioned Onchidium peronii from Inhaca Island, Mozambique (ca. 26°S). Given that no information is provided for species identification, this record is not taken for granted. Onchidium peronii was likely confused with P. verruculata (unit #5), which our material indicates is present in Inhaca, or even P. madagascariensis, known from South Africa to western India (Fig. 6). The fact that the slugs were found on sand (Macnae and Kalk 1958: 128) could suggest that they saw P. verruculata (unit #5).

Solem (1959: 39) did not report any new material or localities for P. peronii. The references that he mentioned (e.g., Bretnall 1919; Hoffmann 1928) are already commented on above. His proposed distribution (“from the Red Sea and Mauritius to New Caledonia, Samoa, and the Marshall Islands”) is not fully accurate because it is based on the assumption that people never made any mistakes when identifying P. peronii, which is unfortunately not true. Solem (1959: 38) mentioned what he thought were the three “most obvious” of the “numerous differences” between O. peronii and O. verruculatum: distribution of branchial plumes (dorsal gills) on the notum, relative position of the pneumostome and the anus, and relative width of the hyponotum and pedal sole. But those features vary among individuals and should not be used for species identification.

Marcus and Marcus (1960: 877) described Peronia peronii from the Maldives based on eight specimens. Given that they report a maximum animal length of 155 mm, a long (4.5 mm) spine of the accessory penial gland, as well as a retractor muscle inserting near the heart, there is little doubt that they did examine P. peronii (Table 4). Later, Marcus and Marcus (1970: 213) added that they observed a retractor muscle inserting near the nerve ring in another of their specimens from the Maldives, which also is compatible with our present observations: a vestigial retractor muscle was even observed here in P. peronii (Table 4). Some of the material examined from historical museum collections for the present work also came from the Maldives (ANSP 304860).

Webb et al. (1969: 107–112) described copulatory mechanisms in specimens they identified as O. peronii. It is unclear from where those specimens were, possibly South Africa. At any rate, given that they illustrate a spine of the accessory penial gland which is only 1.4 mm long (Webb et al. 1969: 110, fig. 3), they did not examine individuals of P. peronii.

It is not possible to determine whether Marcus and Marcus (1970: 213) examined an individual of Peronia peronii from Madagascar because they do not provide the key features that characterize it. They could have seen a large individual of P. madagascariensis instead. Britton (1984: 183) merely mentioned the fact that Marcus and Marcus (1970) accepted only two valid species names (P. peronii and P. verruculata), which is not strictly exact because Marcus and Marcus (1970) did not address the nomenclatural status of P. tongana and did say that P. branchifera was close to P. verruculata but not that it was its synonym.

Patil and Kulkarni (2013) reported Onchidium peronii from Uran City, near Mumbai, India, but it is impossible to determine what species they saw (most likely it was P. madgascariensis or the unit #4 of P. verruculata, or both).

Many chemical studies have mentioned P. peronii in the past few decades. However, the name P. peronii was used arbitrarily. The individuals used for the extraction of natural products may not have been properly identified. Biskupiak and Ireland (1985) extracted peroniatriols from specimens identified as P. peronii from Guam. Peronia peronii is undeniably present in Guam. However, it is possible that P. verruculata (unit #1) could be present there as well. Pietra (1990: 145) mentioned peroniatriols in Peronia peronii from Micronesia where more than one species may be found. Arimoto et al. (1993) did not indicate where specimens of P. peronii and O. verruculatum were collected. In Japan, where the individuals used by Arimoto et al. (1993) possibly came from, there are four Peronia species which are all cryptic externally. Pietra (2002: 290) briefly cited peroniatriols in P. peronii based on the work by Arimoto et al. (1993). Finally, the antibacterial peptide extracted from individuals of Peronia peronii from the Persian Gulf (Bitaab et al. 2015) was most likely extracted from individuals of either P. verruculata (unit #4), or P. madagascariensis, or both (Fig. 6). The same general remark applies to ecological studies: Morrisey et al. (2010: 72) listed (with no justification for species identification) the presence of Peronia peronii in mangroves of the estuary of the Mtata River (31°57'S), South Africa; most likely, Morrisey et al. (2010: 72) encountered P. madagascariensis instead.

Finally, a few last words on P. peronii in phylogenetic studies. Dayrat et al. (2011: 428) and White et al. (2011: 4) identified a specimen from Guam (CASIZ 180486) as Peronia peronii, which is specimen [443] in the present study (Fig. 2). The specimen tentatively identified as Peronia cf. peronii from Mozambique (NHMUK 20060414) by Dayrat et al. (2011: 428) belongs to P. madagascariensis, which is specimen [735] in the present study (Fig. 2). The DNA sequences of the specimen from Guam were used again in several studies (e.g., Gaitán-Espitia et al. 2013; Harasewych et al. 2015).

Peronia okinawensis Dayrat & Goulding, sp. nov.

Figs 17, 18, 19, 20

Type material

Holotype. Japan • holotype, hereby designated, 27/25 mm [696-4 H]; Okinawa, Kunigami, Bay just SE of Cape Hedo; 26°51.803'N, 128°15.863'E; 3 Jul 2004; G Paulay, J Jeller, M Malay & Y Hiratsuka leg.; reef flat; UF 352288.

Additional material examined

Japan • 2 specimens 25/20 mm [696-3] and 20/17 mm [696-2]; same collection data as for the holotype; UF 352288.

Distribution

(Fig. 6). Endemic to Okinawa, Japan.

Etymology

Peronia okinawensis is named after its type locality: okinawensis is a latinized adjective that agrees in gender (feminine) with the generic name (ICZN 1999: Article 31.2).

Habitat

The only specimens known were found on a reef flat. Peronia okinawensis seems to be rare compared to P. verruculata (unit #1) but may be more abundant at some other sites in Okinawa. It would be interesting, in the future, to map in detail at what exact sites the three Peronia species that are sympatric in Okinawa (P. okinawensis, P. peronii, and P. verruculata) overlap or not, in Okinawa and possibly in the rest of the Ryukyu Islands.

Color and morphology

No picture of live animals is available. The color of preserved specimens is beige mottled with darker areas dorsally and whitish ventrally. The dorsal notum of live animals is covered by dozens of papillae of various sizes. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (8–15). The largest specimens are 27 mm long.

Digestive system

(Figs 17A, 18). Examples of radular formulae are presented in Table 5. The median cusp of the rachidian teeth is approximately 45 μm long. The hook of the lateral teeth is approximately 110 μm long. The intestinal loops are of type I, with a transitional loop oriented between 12 to 3 o’clock.

Figure 17. 

Peronia okinawensis, Japan, Okinawa, holotype [696-4 H] (UF 352288) A digestive system, dorsal view, the arrow indicates the orientation of the transitional loop B posterior, hermaphroditic (female) reproductive system C anterior, male, copulatory apparatus. Scale bars: 3 mm (A–C). Abbreviations: ag accessory penial gland, dd deferent duct, ddg dorsal digestive gland, fgm female gland mass, hg hermaphroditic gland, i intestine, ms muscular sac, ov oviduct, pdg posterior digestive gland, ps penial sheath, rm retractor muscle, rs receptaculum seminis, sp spermatheca, st stomach, v vestibule.

Figure 18. 

Radula, Peronia okinawensis, Japan, Okinawa A, B holotype [696-4 H] (UF 352288) C–F [696-2] (UF 352288) A left half rows of teeth B rachidian and innermost lateral teeth C rachidian and innermost lateral teeth D rachidian and lateral teeth E lateral teeth F outermost lateral teeth. Scale bars: 200 μm (A), 80 μm (B), 20 μm (C, F), 60 μm (D), 100 μm (E).

Reproductive system

(Figs 17B, C, 19, 20). In the anterior (male) parts, the muscular sac of the accessory penial gland is less than 15 mm long. The hollow spine of the accessory penial gland is narrow, elongated, and straight or slightly curved, and its shape (including at its tip) varies between individuals. Its length ranges from 1.8 mm ([696-3] UF 352288) to 2.3 mm ([696-4 H] UF 352288). Its diameter at the conical base ranges from 240 to 300 μm. Its diameter at the tip ranges from 115 to 150 μm. The retractor muscle is shorter or longer than the penial sheath and inserts near the heart. Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 35 μm long.

Diagnostic features

(Table 4). Peronia okinawensis is characterized by a unique combination of anatomical traits: muscular sac shorter than 15 mm, intestinal loops of type I (with a transitional loop oriented between 12 and 3 o’clock), retractor muscle inserting near the heart.

Remarks

A new species name is needed because no existing name applies to the species described here. The specimen [696-2] was tentatively identified as Peronia cf. verruculata by Dayrat et al. (2011). This identification should be disregarded because the specimen [696-2] belongs to the species described here (Figs 24). Peronia okinawensis is one of the four Peronia species in Japanese waters (Fig. 6). For a comparison of their geographic range, see remarks on P. setoensis. For their identification, see the identification key as well as Table 4. It is possible that P. okinawensis is not strictly endemic to Okinawa.

Figure 19. 

Penial hooks, Peronia okinawensis, Japan, Okinawa A, B holotype [696-4] (UF 352288) C, D [696-3] (UF 352288). Scale bars: 4 μm (A, C, D), 2 μm (B).

Figure 20. 

Accessory penial gland spine, Peronia okinawensis, Japan, Okinawa A holotype [696-4] (UF 352288) B [696-3] (UF 352288) C [696-2] (UF 352288) D same as A; E same as B; F same as C. Scale bars: 400 μm (A–C), 40 μm (D–F).

Peronia madagascariensis (Labbé, 1934a)

Figs 21, 22, 23, 24, 25

Paraperonia madagascariensis Labbé, 1934a: 199, fig. 15.

Paraperonia jousseaumei Labbé, 1934a: 198, figs 12–14. Syn. nov.

Type material

Holotype (Paraperonia madagascariensis). Madagascar • holotype, by monotypy, 40/40 mm; Fort Dauphin [Taolagnaro]; 1932; Décary leg.; MNHN-IM-2000-33680. Originally, no jar clearly labeled as the type material of P. madagascariensis was found at the MNHN, but the holotype could be traced back. The original description of P. madagascariensis is based on a single individual (40/38 mm) from Fort-Dauphin collected by Décary (the French botanist Raymond Décary [1891–1973]) in 1932. Only one old jar was found at the MNHN with a specimen collected from Fort-Dauphin (MNHN-IM-2000-33680). The information on the label (specimen collected by Décary in 1932) matches the information provided in Labbé’s original description of P. madagascariensis, and even the specimen size matches. Therefore, that specimen is considered to be the holotype by monotypy of P. madagascariensis. The holotype was dissected by Labbé. The radula, the posterior (hermaphroditic) reproductive parts, and the male parts are all missing. The intestinal loops are of type V (Fig. 21A).

Figure 21. 

Peronia madagascariensis A–D digestive system, dorsal view, with intestinal loops of type V E posterior, hermaphroditic (female) reproductive system A holotype, Paraperonia madagascariensis, Madagascar (MNHN-IM-2000-33680) B paralectotype, Paraperonia gondwanae, Mumbai, western India (MNHN-IM-2000-33682) C paralectotype, Paraperonia gondwanae, Red Sea (MNHN-IM-2000-33683) D Madagascar, [5501] (MNHN-IM-2009-16392) E same as D. Scale bars: 5 mm (A–D), 2 mm (E). Abbreviations: dd deferent duct, ddg dorsal digestive gland, fgm female gland mass, hg hermaphroditic gland, i intestine, ov oviduct, pdg posterior digestive gland, rs receptaculum seminis, sp spermatheca, st stomach.

Syntypes (Paraperonia jousseaumei). The type material of Paraperonia jousseaumei could not be located at the MNHN. The original description of P. jousseaumei was based on ten individuals (45/38 to 40/30 mm) from the Red Sea (“Mer Rouge”) collected by Jousseaume in 1892. Only two old jars were found at the MNHN with that collecting information. One of them contains specimens that are part of the type series of P. gondwanae because the specific name “gondwanae” is written on an old label (MNHN-IM-2000-33683). The three labels of the other jar (MNHN-IM-2014-7993) say: “Peronia Mer Rouge Mr Jousseaume n°15, 1892,” “Oncidium [written over “Oncidiella”] peronii Cuvier Mer Rouge M. Jousseaume n°15-1892,” and, for unknown reasons, “60.” This jar contains six specimens of Peronia, from 60/45 to 25/15 mm, two of which were dissected, possibly by Labbé. The intestinal loops of the two dissected specimens are of type I and thus are not in agreement with Labbé’s (1934a: fig. 12) original illustration of the intestinal loops of type V in P. jousseaumei. Also, the sizes and the number of individuals do not match the original description of P. jousseaumei. Those specimens could possibly be some of the eight non-type specimens that Labbé (1934a: 190) mentioned in his re-description of Peronia peronii collected by Jousseaume from the Red Sea (“Mer Rouge”) in “1852” (likely a mistake for 1892). Given that Labbé does not specify their size, it is not possible to know to what species Labbé thought those specimens belong exactly (MNHN-IM-2014-7993).

Additional material examined

South Africa • 2 specimens 35/23 mm [5841] and 18/13 mm [5842]; KwaZulu-Natal, Durban, Treasure Beach; 29°57.294'S, 30°59.514'E; 18 Nov 2010; D Herbert and L Davis leg.; rocky intertidal zone; NMSA W7547.

Mozambique • 1 specimen 42/37 mm [735]; Cabo Delgado Province, Pemba, Wimbi Beach, Pemba Beach Hotel; 12°58'S, 40°32'E; 14 Jul 2006; DG Reid leg.; on shady rock at base of limestone cliff, in upper eulittoral behind intertidal platform; NHMUK 20060414.

Madagascar • 1 specimen 55/40 mm [5500]; Ambatobe, près Soamanitse; 25°27.4'S, 44°57.4'E; 24 May & 7 Jun 2010; MNHN Expedition Atimo Vatae leg.; st BM02, 0–1 m; MNHN-IM-2009-16391. • 1 specimen 40/35 mm [5504]; same collection data as for the preceding; MNHN-IM-2009-16412. • 1 specimen 40/30 mm [5501]; Ambatomainty; 25°26.3'S, 44°56.5'E; 25 May 2010; MNHN Expedition Atimo Vatae leg.; st BM03, 0–1 m; MNHN-IM-2009-16392. • 1 specimen 55/40 mm [5502]; same collection data as for the preceding; MNHN-IM-2009-16393. • 1 specimen 55/40 mm [5503]; Ambatobe, Bavarama; 25°27.9'S, 44°57.6'E; 28 & 29 May 2010; MNHN Expedition Atimo Vatae leg.; st BM06, 0–1 m; MNHN-IM-2009-16396. • 1 specimen 40/35 mm [5506]; same collection data as for the preceding; MNHN-IM-2009-16418.

Oman • 1 specimen 10/7 [703]; Muscat, Cemetery Bay; 23°37.250'N, 58°36.016'E; 9 Feb 2004; G Paulay & M Claereboudt leg.; coral community, reef slope, on ophiolitic bedrock and rubble; UF 332088.

Additional material examined

(historical museum collections). Oman • 3 specimens 80/60 mm; Qurm Beach, near Muscat; 23°37.56'N, 58°28.86'E; 26 Jan 2005; V Bonito, M Claereboudt & G Paulay leg.; intertidal rocky shore; UF 368019.

Iran • 3 specimens 80/65 mm to 75/65 mm; Persian Gulf, Strait of Hormuz, Qeshm Island; 18 Apr 1937; G Thorson leg.; st 69; NHMD 635302.

Yemen • 1 specimen 55/55 mm; Socotra, off Quadub; 12°39.015'N, 53°55.730'E; 18 Mar 1999; Salim Al-Moghrabi (from N Yonow’s personal collection) leg.; intertidal, ST-064 SAM-1; SMF 358305.

South Africa • 1 specimen 70/45 mm; Port Natal, Durban; 30S, 31E; Wahlberg leg.; littoral rocky bottom; SMNH 180711.

GenBank and BOLD sequences

One COI sequence was obtained from BOLD (LGEN099-14) for an individual identified as Onchidium verruculatum and collected from Dwarka, Gujarat, on the western coast of India (ca. 22°N), which is the easternmost known locality for P. madagascariensis. A second COI sequence was obtained from GenBank (LC027608) for an individual identified as Peronia sp. and collected from the coast of Iran in the Persian Gulf. Both sequences were unpublished.

Distribution

(Fig. 6). From South Africa to the Red Sea and western India (ca. 22°N): South Africa, Mozambique, Madagascar (type locality of P. madagascariensis), Gulf of Oman, Iran (Strait of Hormuz), Yemen (Socotra), India (Mumbai, Gujarat), Red Sea (type locality of P. jousseaumei). All records are new except for the type locality in Madagascar. Peronia madagascariensis is, so far, not present in Mauritius.

Etymology

Peronia madagascariensis was named after its type locality, Madagascar. Peronia jousseaumei was named after Félix Pierre Jousseaume [1835–1921], a medical doctor and malacologist who collected many specimens from the Red Sea preserved at the MNHN and which Labbé (1934a) studied for his monograph on onchidiids.

Habitat

Peronia madagascariensis is found in the rocky intertidal, like most other Peronia slugs.

Color and morphology

No picture of live animals was available. The color of preserved specimens is not different from other species (greyish brown and mottled with darker and lighter areas dorsally, and light brown greyish ventrally). The dorsal notum of live animals is covered by dozens of papillae of various sizes. In large individuals, dorsal papillae can be particularly tall (easily up to 4 mm), even in preserved specimens, and are evenly distributed over the entire notum. Preserved, they are very difficult to distinguish from retracted dorsal gills in the posterior half of the notum, but they are regular papillae with or without eyes. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (from 12 to 18). Dorsal gills seem taller and denser than in other species. The largest specimens in our fresh material are 55 mm long but two additional museum specimens are much longer (80 mm).

Digestive system

(Figs 21A–D, 22). Examples of radular formulae are presented in Table 5. The median cusp of the rachidian teeth is approximately 55 μm long. The hook of the lateral teeth is approximately 100 to 130 μm long. The intestinal loops are of type V.

Figure 22. 

Radula, Peronia madagascariensis, South Africa, [5841] (NMSA W7547) A right half rows of teeth B rachidian and innermost lateral teeth C rachidian and innermost lateral teeth D lateral teeth E lateral teeth, frontal view F outermost lateral teeth. Scale bars: 200 μm (A), 20 μm (B, E, F), 40 μm (C), 100 μm (D).

Reproductive system

(Figs 21E, 2325). In the anterior (male) parts, the muscular sac of the accessory penial gland is less than 15 mm long. The hollow spine of the accessory penial gland is narrow, elongated, and straight or slightly curved, and its shape (including at its tip) varies between individuals. Its length ranges from 2 mm ([5502] MNHN-IM-2009-16393) to 2.4 mm ([5500] MNHN-IM-2009-16391). Its diameter at the conical base ranges from 200 to 230 μm. Its diameter at the tip ranges from 70 to 80 μm. The retractor muscle is shorter or longer than the penial sheath and inserts near the heart. Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 100 μm long.

Figure 23. 

Anterior, male, copulatory apparatus, Peronia madagascariensis A Madagascar, [5501] (MNHN-IM-2009-16392) B South Africa, [5841] (NMSA W7547). Scale bars: 5 mm (A), 2 mm (B). Abbreviations: ag accessory penial gland, dd deferent duct, ms muscular sac, ps penial sheath, rm retractor muscle, v vestibule.

Figure 24. 

Penial hooks, Peronia madagascariensis, Madagascar A, C [5500] (MNHN-IM-2009-16391) B, D [5504] (MNHN-IM-2009-16412) E [5506] (MNHN-IM-2009-16418) F [5501] (MNHN-IM-2009-16392). Scale bars: 60 μm (A), 100 μm (B), 20 μm (C, D), 40 μm (E), 10 μm (F).

Figure 25. 

Accessory penial gland spine, Peronia madagascariensis, Madagascar A, E [5500] (MNHN-IM-2009-16391) B, F [5502] (MNHN-IM-2009-16393) C, G [5504] (MNHN-IM-2009-16412) D, H [5506] (MNHN-IM-2009-16418). Scale bars: 400 μm (A–D), 20 μm (E–H).

Diagnostic features

(Table 4). Peronia madagascariensis is characterized by a unique combination of two anatomical traits: intestinal loops of type V and a spine of the accessory penial gland longer than 2 mm.

Remarks

The name Paraperonia madagascariensis clearly applies to a Peronia species because of the dorsal gills on the notum of the holotype. The holotype was entirely dissected by Labbé. The radula, the posterior (hermaphroditic) reproductive parts, and the anterior copulatory apparatus are missing. The intestinal loops are of type V (Fig. 21A), as illustrated by Labbé (1934a: fig. 17). The name Peronia madagascariensis applies to the species described here because it is, according to our molecular data, the only Peronia species with intestinal loops of type V along the eastern African coast, from South Africa to the Persian Gulf and western India, including Madagascar. Note that some of our fresh material was collected only 150 km east of the type locality in southern Madagascar. Some internal characters described by Labbé (1934a: 199) could not be verified on the holotype because most internal parts are missing, but they are similar to the species described here. In particular, the length of the spine of the accessory penial gland (2 mm) is compatible with what was observed in our material.

Additional, non-type specimens were found in historical museum collections which could be identified as P. madagascariensis due to the presence of intestinal loops of type V, from Oman (UF 368019), the Strait of Hormuz (NHMD 635302), and Socotra (SMF 358305). Those localities, however, are all already included within the known distribution of P. madagascariensis based on our DNA sequences, as the Strait of Hormuz is very close to the Gulf of Oman. Finally, one of the “a” paralectotypes of Labbé’s (1934a: 199) Paraperonia gondwanae from Bombay (MNHN-IM-2000-33682), with intestinal loops of type V (Fig. 21B), belongs to P. madagascariensis. Note that two of those museum specimens are longer (80 mm) than our fresh material (less than 55 mm).

Peronia slugs with intestinal loops of type V are without doubt present in the Red Sea. For instance, one of the “c” paralectotypes of Labbé’s (1934a: 200) Paraperonia gondwanae from Suez (MNHN-IM-2000-33683) is characterized by intestinal loops of type V (Fig. 21C), which means that it does not belong to P. verruculata (characterized by intestinal loops of type I). Labbé’s (1934a) Paraperonia jousseaumei, with the Red Sea as type locality, is also characterized by intestinal loops of type V. Even though the type material of P. jousseaumei could not be located at the MNHN, Labbé’s (1934a: fig. 12) drawing of the internal anatomy of P. jousseaumei clearly illustrates intestinal loops of type V. Given that P. madagascariensis is widespread from South Africa all the way to western India, including the Strait of Hormuz, it is accepted here that it also is distributed in the Red Sea. That, however, will still need to be confirmed with fresh material from both the Red Sea and the Gulf of Aden. If it appears that the populations of Peronia slugs with intestinal loops of type V from the Red Sea are a distinct species, then the name P. jousseaumei could apply to them and be valid. Finally, given that P. madagascariensis is present in the Strait of Hormuz, it most likely also is distributed in the rest of the Persian Gulf, which hopefully will be confirmed at some point with fresh material.

Even though the names Peronia madagascariensis and Peronia jousseaumei were never used prior to the present contribution, they are not regarded as new combinations because Paraperonia has already been regarded as a synonym of Peronia by Britton (1984: 182) and because it has also been made clear that the genus Peronia included all species of slugs with dorsal gills (e.g., Dayrat et al. 2017: 1861).

The specimen [703] from Oman was tentatively identified as Peronia sp. 2 by Dayrat et al. (2011) but it clearly belongs to P. madagascariensis (Fig. 2). Also, note that its COI sequence was resubmitted to GenBank because the old one (GenBank HQ660044) was inaccurate. The specimen [735] from Mozambique was tentatively identified as Peronia cf. peronii by Dayrat et al. (2011). This identification should be disregarded because the specimen [735] belongs to P. madagascariensis (Fig. 2).

A specimen from Durban (30°S), South Africa, preserved in Stockholm (SMNH 180711) identified as O. verruculatum by Hoffmann (1928: 44, 73) is identified here as P. madagascariensis because of its intestinal loops of type V (Table 4). Various records of Onchidium peronii, O. savignyi, and Onchidium verruculatum from Natal, South Africa (Krauss 1848: 72; Sturany 1898: 73; Collinge 1910: 171–172; Connolly 1912: 224–225, 1939: 454; Webb 1969) most likely are records of Peronia madagascariensis, although P. verruculata (unit #5) could also be present in northeastern South Africa because it is known in Maputo, southern Mozambique (ca. 26°S).

Peronia platei (Hoffmann, 1928)

Figs 26, 27, 28, 29, 30, 31, 32

Onchidium platei Hoffmann, 1928: 51–53, figs 9, 10, pl. 3, figs 11, 12.

Type material

Lectotype and paralectotypes. French Polynesia • lectotype, hereby designated, 18/10 mm; Eimeo [Moorea], Tahiti; 1851–1853; Eugenie Expedition leg.; st 1245–9, in the barrier reef; SMNH-Type-7537. • 2 paralectotypes, 16/10 mm and 16/10 mm; same collection data as for the lectotype; SMNH-Type-7537. • 4 paralectotypes, 17/10 mm, 16/12 mm, 15/11 mm, and 10/7 mm; Tahiti; Dec 1846; Reinhardt, Galathea Expedition 470 leg.; NHMD 613754. • 1 paralectotype, 7/5 mm; Tahiti; Reinhardt, Galathea Expedition 471 leg.; NHMD 613755. • 1 paralectotype, 15/10 mm; Tahiti; Reinhardt, Galathea Expedition 472 leg.; NHMD 613756.

Additional material examined

Hawaii • 2 specimens 12/10 mm [706] and 12/12 mm [5380]; Molokai, Puko’o; 21°04.313'N, 156°48.001'W; 27 Jan 2003; V Bonito leg.; on rocks; UF 303653. • Oahu, Ala Moana Beach Park; 21°17.158'N, 157°50.827'W; 1 specimen 30/20 mm [6160]; 7 Oct 2018; TC Goulding leg.; st 264, intertidal rocks, night tide; BPBM 284527. • 1 specimen 30/20 mm [6161]; same collection data as for the preceding; BPBM 284528.

Papua New Guinea – Madang • 1 specimen 14/12 mm [5405]; Rempi Area, SW Hargun Island; 05°01.6'S, 145°47.9'E; 15 & 20 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM24, night tide; MNHN-IM-2013-13762. • 1 specimen 20/17 mm [5412]; Rempi Area, Barag Island; 05°01.1'S, 145°47.9'E; 15 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM25, fringing reef on narrow barrier island; MNHN-IM-2013-13351. • 1 specimen 12/10 mm [5410]; Riwo Waters; 05°08.9'S, 145°48.2'E; 26 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM40, sandy beach and intertidal rocks; MNHN-IM-2013-15765. • 1 specimen 14/12 mm [5464]; Wonad Island; 05°08.1'S, 145°49.3'E; 27 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM41, sandy beach and intertidal rocks; MNHN-IM-2013-15871.

Additional material examined

(historical museum collections). French Polynesia • 2 specimens 15/10 mm and 13/8 mm; Tuamotu Archipelago, NE side, Anaa Atoll; 17°20'S, 145°30'W; 27 Oct 1967; NGS-SBM Marquesa Expedition MV “Pele” 1967 leg.; WAM S26717. • 2 specimens 7/5 mm and 5/4 mm; Tuamotu Archipelago, Marutea Atoll; 17S, 143°10.02'E; Aug 1903; LG Seurat leg.; AM C.17073.

Hawaii • 15 specimens from 18/15 mm to 8/8 mm; Oahu, Kailua Bay, Mokapu Point; 21°28.02'N, 157°43.98'E; WF Ponder and EA Kay leg.; 7 Apr 1974; on rocks, semi-sheltered and exposed platforms; AM C.214245.

Kiribati • 8 specimens from 10/9 mm to 3/3 mm; Gilbert Islands, Apamama [Abemama]; 00S, 173E; 1917–1918; S Bock’s Pacific Expedition leg.; sand, inside lagoon; SMNH 106488.

Distribution

(Fig. 6). West Pacific: Papua New Guinea, French Polynesia (Tuamotu and Tahiti), Kiribati, and Hawaii. All records are new except for the type locality in Tahiti.

Etymology

Peronia platei was named after German zoologist Ludwig Hermann Plate [1862–1937], professor of zoology at the University of Jena and author of a monograph on onchidiids (Plate 1893).

Habitat

Peronia platei is found primarily in the rocky intertidal. According to the label, specimens from Kiribati were collected on sand inside a lagoon (P. sydneyensis and P. willani are also known to be found on sand).

Color and morphology of live animals

(Fig. 26). No picture of live animals was available for specimens from the West Pacific. The description of the color of live animals is based on Hawaii individuals. The dorsal notum is uniformly very dark grey, almost black, including papillae. The hyponotum is light yellowish. The foot is light yellowish to orange. The ocular tentacles are grey, like the head. The dorsal notum of live animals is covered by dozens of papillae of various sizes. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (from 7 to 10). The papillae with dorsal eyes cannot be counted in specimens from Hawaii because the notum is too dark and because eye pigmentation tends to fade in preservation. The largest specimens are 30 mm long in Hawaii and 20 mm in Papua New Guinea.

Figure 26. 

Live animals, Peronia platei, Hawaii, Oahu A dorsal view, 30 mm long [6161] (BPBM 284528) B dorsal view, 30 mm long [6160] (BPBM 284527) C ventral view, same as A; D ventral view, same as B.

Digestive system

(Figs 27, 28). Examples of radular formulae are presented in Table 5. The median cusp of the rachidian teeth is approximately 30 to 35 μm long. The hook of the lateral teeth is approximately 60 to 90 μm long. The intestinal loops are of type V.

Figure 27. 

Digestive system, dorsal view, Peronia platei, with intestinal loops of type V A lectotype, French Polynesia, Moorea (SMNH-Type-7537) B Hawaii, Oahu [6160] (BPBM 284527) C Papua New Guinea, Madang [5412] (MNHN-IM-2013-13351). Scale bars: 2 mm (A–C). Abbreviations: ddg dorsal digestive gland, i intestine, pdg posterior digestive gland, st stomach.

Figure 28. 

Radula, Peronia platei A Papua New Guinea, Madang [5405] (MNHN-IM-2013-13762) B Hawaii, Oahu [6161] (BPBM 284528) C–E Hawaii, Molokai [706] (UF 303653) F [5380] (UF 303653) A right half rows of teeth B rachidian and innermost lateral teeth C rachidian and innermost lateral teeth D lateral teeth E outermost lateral teeth F lateral teeth. Scale bars: 200 μm (A), 20 μm (B, E), 30 μm (C), 100 μm (D), 80 μm (F).

Reproductive system

(Figs 2932). In the posterior (hermaphroditic) parts, the deferent duct and the oviduct are straight. In the anterior (male) parts, the muscular sac of the accessory penial gland is less than 5 mm long. The hollow spine of the accessory penial gland is narrow, elongated, and straight or slightly curved, and its shape (including at its tip) varies between individuals. Its length ranges from 0.8 mm ([706] UF 303653) to 0.9 mm ([6161] BPBM 284528) in Hawaii and from 0.7 mm ([5405] MNHN-IM-2013-13762) to 1 mm ([5412] MNHN-IM-2013-13351) in Papua New Guinea. Its diameter at the conical base ranges from 95 to 100 μm (Hawaii) and from 65 to 80 μm (Papua New Guinea). Its diameter at the tip ranges from 25 to 30 μm (Hawaii) and from 20 to 30 μm (Papua New Guinea). The retractor muscle is shorter or longer than the penial sheath and inserts at the posterior end of the visceral cavity. Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 60 μm long in Hawaii and less than 20 μm long in Papua New Guinea.

Figure 29. 

Posterior, hermaphroditic (female) reproductive system, Peronia platei A Papua New Guinea, Madang [5412] (MNHN-IM-2013-13351) B Hawaii, Oahu [6160] (BPBM 284527). Scale bars: 3 mm (A, B). Abbreviations: dd deferent duct, fgm female gland mass, hg hermaphroditic gland, ov oviduct, rs receptaculum seminis, sp spermatheca.

Figure 30. 

Anterior, male, copulatory apparatus, Peronia platei A lectotype, French Polynesia, Moorea (SMNH-Type-7537) B Papua New Guinea, Madang [5412] (MNHN-IM-2013-13351) C Hawaii [706] (UF 303653). Scale bars: 5 mm (A), 3 mm (B), 2 mm (C). Abbreviations: ag accessory penial gland, dd deferent duct, ms muscular sac, ps penial sheath, rm retractor muscle, v vestibule.

Diagnostic features

(Table 4). Peronia platei is cryptic with P. setoensis. Both species share the same combination of anatomical traits: intestinal loops of type V, retractor muscle inserting at the posterior end of the visceral cavity, a spine of the accessory penial gland from 0.8 to 1 mm long (P. platei) and from 0.9 to 1.2 mm long (P. setoensis). The diameter of the spine of the accessory penial gland at its tip is larger in P. platei (25 to 30 μm) than in P. setoensis (less than 25 μm) but that may be simply due to limited sampling. Peronia platei and P. setoensis are both distributed in the West Pacific but they are not sympatric based on current data (Fig. 6).

Remarks

Onchidium platei applies to the species described here because the anatomy of the lectotype is identical to the anatomy of our material (Table 4): gills on the dorsal notum; muscular sac of the accessory penial gland less than 5 mm long; spine of the accessory penial gland 0.9 mm long (observed by transparency); intestinal loops of type V; seven dorsal papillae with eyes. Our molecular analyses show that the species described here is widespread across the West Pacific, from Papua New Guinea to Hawaii. There is no reason to think that the populations in French Polynesia (type locality of O. platei) are a distinct species. This, however, will have to be confirmed with fresh material from French Polynesia, preferably from Moorea, the type locality. All eight paralectotypes (also from Tahiti) also belong to the same species.

Hoffmann’s (1928: 51–53, figs 9, 10, pl. 3, figs 11, 12) original description, which is quite detailed, needs to be briefly commented on. Hoffmann mentions that dorsal gills are lacking but they are undoubtedly present in the lectotype and all paralectotypes (dorsal gills are often hard to see in preserved animals). The anatomical traits he describes agree with our observations on the type material. The intestinal loops, Hoffmann says, are of type I but slightly different from the regular type I due to the absence of a loop. Hoffmann calls it a type Ia. His illustration of it clearly represents a type V (Hoffmann 1928: pl. 3, fig. 11). The spine of the accessory penial gland is 1 mm long and the retractor muscle attaches to the posterior end of the visceral cavity. According to Hoffmann (1928: 53), O. platei is most closely related to O. tumidum Semper, 1880 and O. nebulosum Semper, 1880 but differs from them based on the penis size. Onchidium tumidum was recently transferred to Paromoionchis (Dayrat et al. 2019a), and O. nebulosum (type locality in Palau) applies to a Peronia species but is regarded here as a nomen dubium (see general discussion).

Additional specimens were found in historical museum collections which could be identified as P. platei mostly based on the intestinal loops of type V, the specimen size, and their geographic origin. Specimens from Kiribati (SMNH 106488) are especially interesting because they confirm the presence of specimens similar to P. platei far from Hawaii and Papua New Guinea, which strongly supports the assumption that P. platei is widespread across the entire West Pacific. Note that those specimens from Kiribati are not identified as P. setoensis (which is anatomically cryptic with P. platei) because P. setoensis is found in much colder waters (33°N) in Japan (Fig. 6).

Labbé (1934a: 224) merely mentioned Onchidium platei as one of the valid Onchidium species names. Ruthensteiner (1997) briefly commented on the anatomy of the lung of Onchidium cf. branchiferum, based on specimens from Hawaii. Those were most likely specimens of Peronia platei, the only Peronia species found in Hawaii. Finally, note that the specimen [706] (UF 303653) was tentatively referred to as Peronia sp. 1 by Dayrat et al. (2011).

Figure 31. 

Penial hooks, Peronia platei A, C Hawaii, Oahu [6161] (BPBM 284528) B, D Papua New Guinea, Madang [5412] (MNHN-IM-2013-13351). Scale bars: 40 μm (A), 20 μm (B), 10 μm (C), 2 μm (D).

Figure 32. 

Accessory penial gland spine, Peronia platei A–C, F, G Hawaii, Oahu D, E, H, I Papua New Guinea, Madang A [706] (UF 303653) B [6160] (BPBM 284527) C [6161] (BPBM 284528) D [5412] (MNHN-IM-2013-13351) E [5405] (MNHN-IM-2013-13762) F same as A; G same as B; H same as D; I same as E. Scale bars: 100 μm (A, E), 200 μm (B, D), 150 μm (C), 6 μm (F, H, I), 10 μm (G).

No Peronia slug from Hawaii was positively demonstrated to belong to P. verruculata (unit #1), which is characterized by intestinal loops of type I. Therefore, Hoffmann’s (1928: 44, 73) record of O. verruculatum from Hawaii is interpreted here as a misidentification of P. platei. Labbé (1934a: 193), Solem (1959: 39), and Marcus and Marcus (1970: 213) all assumed that P. verruculata was present in Hawaii based on Hoffmann’s (1928) study, without collecting or examining any new material.

Onchidella evelinae Marcus & Burch, 1965 was described based on small specimens (average length 6 mm) from Eniwetok Atoll, Marshall Islands (ca. 11°N, 162°E). The type material was deposited at the Museum of Zoology, University of Michigan, but could not be located there (personal communication from the collection manager, Dr. Taehwan Lee). Onchidella evelinae is a misidentification for one of the onchidiid species present in the Marshall Islands: it cannot refer to Onchidella slugs because an accessory penial gland is mentioned in the original description and because Onchidella is not present in the middle of the West Pacific. The Marshall Islands are within the distribution range of P. platei (Fig. 6), but a detail from the original description (the internal organs can be seen through the dorsal notum) suggests that O. evelinae does not refer to Peronia slugs because their notum is too thick for internal organs to be seen through it. Peronia peronii is also present in the Marshall Islands (Fig. 6), but, given the very small size of the specimens and that they were sexually mature, it is most unlikely that O. evelinae is a junior synonym of P. peronii (Fig. 6). The size of the spine of the accessory penial gland (1.3 mm) reported in the original description of O. evelinae is compatible with what is currently known (< 1 mm) for P. platei (Table 4). Onchidella evelinae is regarded here as a new junior subjective synonym of Marmaronchis vaigiensis (Quoy & Gaimard, 1825): first, because internal organs can occasionally be seen through its thin notum (e.g., Dayrat et al. 2018: fig. 5E); second, because there are known records (Dayrat et al. 2018: fig. 9) of M. vaigiensis in Pohnpei, Micronesia (ca. 6°N, 158°E), just a few degrees west of the Marshall Islands, and it is very possible that M. vaigiensis also is in the Marshall Islands. The size of the spine of the accessory penial gland (1.3 mm) reported in the original description of O. evelinae is higher than what is currently known for M. vaigiensis (< 1 mm), but that trait does vary intra-specifically.

Peronia setoensis Dayrat & Goulding, sp. nov.

Figs 33, 34, 35, 36, 37, 38

Type material

Holotype. Japan • holotype, hereby designated, 20/15 mm [5383]; Honshu, Wakayama, Nishimuro, near Seto Marine Biological Laboratory; 33°41.504'N, 135°20.179'E; 30 Aug 2014; R. Cumming leg.; exposed rock wall and platform; NSMT-Mo 78985.

Additional material examined

Japan • 3 specimens 13/8 mm [5382], 10/5 mm [5384], and 12/10 mm [5385]; same collection data as for the holotype; NSMT-Mo 78986. • 2 specimens 15/10 mm [3753] and 15/10 mm [3754]; Honshu, Wakayama, Nishimuro, near Seto Marine Biological Laboratory; 33°41.533'N, 135°20.265'E; 2014; T Nakano leg.; NSMT-Mo 78987.

Additional material examined

(historical museum collections). Japan • 1 specimen 23/20 mm; Sagami Bay, Misaki; 1930–1931; Gislén’s Pacific Expedition 1930–1931 leg.; littoral rocky bottom; SMNH 180725.

Distribution

(Fig. 6). Endemic to subtropical waters of Japan: Honshu, Nishimuro, near Seto Marine Biological Laboratory (33N, type locality), Sagami Bay (35°N), and possibly Boso Peninsula, near Sagami Bay (35°N); Kyushu, Nagasaki, 32N (Keferstein 1865a, b, as P. verruculata).

Etymology

Peronia setoensis is named after its type locality, near the Seto Marine Biological Laboratory: setoensis is a latinized adjective that agrees in gender (feminine) with the generic name (ICZN 1999: Article 31.2).

Habitat

(Fig. 33). Peronia setoensis is found in the rocky intertidal. Few individuals are currently known but it may be discovered in additional localities in the future.

Figure 33. 

Habitat, Peronia setoensis, Japan, Honshu, near the Seto Marine Laboratory, type locality, exposed rock wall and platform.

Color and morphology of live animals

(Fig. 34). The dorsal notum is greenish brown, light to dark, mottled with darker and lighter areas, occasionally with yellowish sides. The color of the dorsal papillae varies as that of the background itself. The ventral surface (foot and hyponotum) is yellowish or greyish and can change rapidly in any given individual. The ocular tentacles are brown-grey, like the head. The dorsal notum of live animals is covered by dozens of papillae of various sizes. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (from 8 to 12). The largest specimens are 20 mm long.

Figure 34. 

Live animals, Peronia setoensis, Japan, Honshu A holotype, dorsal view, 20 mm long [5383] (NSMT-Mo 78985) B dorsal view, 10 mm long [5384] (NSMT-Mo 78986) C dorsal view, 12 mm long [5385] (