A review of the land snail genus Alycaeus (Gastropoda, Alycaeidae) in Peninsular Malaysia

Abstract A total of 11 species and 1 subspecies of Alycaeus were recognised in Peninsular Malaysia prior to this study. However, these taxonomic descriptions of Alycaeus taxa were based on limited numbers of examined materials, where a whole spectrum of morphological variations were not accounted for and diagnoses were often provided without sufficient comparison between congeners from across the peninsula. We reviewed Peninsular Malaysian Alycaeus through the examination of 5137 specimens in 522 collection lots from all major museum collections and literature sources. Based on these examined materials, we utilised a more comprehensive revised set of 39 shell and operculum characters, as well as living animal colour to describe all Alycaeus species in this paper. We also noted their habitat and ecology, as well as updated the distribution of each species. Of the 12 previously described taxa, 10 are reconfirmed as present on Peninsular Malaysia (Alycaeus balingensis, Alycaeus carinata, Alycaeus conformis, Alycaeus gibbosulus, Alycaeus kapayanensis, Alycaeus kelantanensis, Alycaeus liratulus, Alycaeus perakensis perakensis, Alycaeus perakensis altispirus and Alycaeus thieroti) and 2 are confirmed as absent from the peninsula (Alycaeus jagori and Alycaeus pyramidalis). A new record of Alycaeus robeleni is reported for Peninsular Malaysia. One species, Chamalycaeus jousseaumei is confirmed as present on the peninsula and is reassigned to Alycaeus. The subspecies Alycaeus perakensis altispirus Möllendorff, 1902, is elevated to species. Examined Peninsular Malaysian materials that do not fit previously recognised species are described as new species. A total of 11 new species are proposed (Alycaeus selangoriensis sp. n., Alycaeus costacrassa sp. n., Alycaeus ikanensis sp. n., Alycaeus alticola sp. n., Alycaeus charasensis sp. n., Alycaeus kurauensis sp. n., Alycaeus regalis sp. n., Alycaeus virgogravida sp. n., Alycaeus senyumensis sp. n., Alycaeus expansus sp. n., Alycaeus clementsi sp. n.). Overall, 23 species of Alycaeus are now recognised in Peninsular Malaysia.


Introduction
The family Alycaeidae Blanford, 1864, is a distinct group of operculated land snails defined by their globular, conical or discoid shell, whorl constriction prior to the aperture and a conspicuous tube at the suture ('breathing tube') which runs from the constriction to whorls prior to the constriction (Godwin-Austen 1889, Kobelt 1902, Egorov 2013. Within Alycaeidae, the genus Alycaeus Baird, 1850, is separated into three subgenera -Alycaeus Baird, 1850, Pincerna Preston, 1907, and Stomacosmethis Bollinger, 1918(Egorov 2013. However, all of these subgenera [including Pincerna (see Páll-Gergely 2017)] remain inadequately diagnosed and will require extensive revision, a task that is beyond the scope of this study. As such, this review will solely focus on species in Peninsular Malaysia that are placed under the genus Alycaeus including two species recently reassigned under Pincerna (Páll-Gergely 2017) -Alycaeus liratulus Preston, 1907, and Alycaeus thieroti Morgan, 1885b, and one species formerly assigned under Chamalycaeus (Kobelt & Möllendorff, 1897) -Alycaeus jousseaumei Morgan, 1885a.
In view of this, we reviewed all Alycaeus species in Peninsular Malaysia using a revised set of 39 shell and operculum characters, as well as living animal colour. We consulted major museum collections in Europe, the United States of America, Singapore and Malaysia that house Alycaeus materials from Peninsular Malaysia, including types. A large collection of recently sampled Alycaeus from across Peninsular Malaysia housed in the BORNEENSIS collection, Universiti Malaysia Sabah, were also studied.
Based on this review, we reconfirmed the presence of 10 previously recognised species on the peninsula (A. balingensis, A. carinata, A. conformis, A. gibbosulus, A. kapayanensis, A. kelantanensis, A. liratulus, A. perakensis perakensis, A. perakensis altispirus and A. thieroti) while 2 species are confirmed as absent on the peninsula (A. jagori and A. pyramidalis). For Alycaeus jagori, records of the species in Perak, Peninsular Malaysia were reported without further elaboration by some workers (Kobelt 1902, Laidlaw 1928, Schilthuizen et al. 1999, Maassen 2001, parts of BOR/MOL collection lots). Benthem Jutting (1948) expressed reservations about the validity of these Peninsular Malaysian records. We examined the syntype of Alycaeus jagori (SMF 109304/1) and concluded that it is indeed distinguished from any Peninsular Malaysian congeners in spire shape, whorl convexity, whorl sculpture and shell size. As such, Alycaeus jagori is herein confirmed as non-existent on Peninsular Malaysia. The source of this mislocation most likely originated from Kobelt and Möllendorff (1897) whereby past workers may have confused the locality of A. jagori (Java) with A. kapayanensis (Perak), both of which were listed next to each other in the text. For Alycaeus pyramidalis, the mislocation is traced back to a mistake by Habe (1965) in which specimens of A. gibbosulus from northern Malay Peninsula were misidentified as A. pyramidalis. Also, a new record of Alycaeus robeleni is reported for Peninsular Malaysia. One species, Chamalycaeus jousseaumei is confirmed as present on the peninsula and is reassigned to Alycaeus. The subspecies Alycaeus perakensis altispirus Möllendorff, 1902, is elevated to species. Overall, we redescribed all 12 previously known species of Alycaeus on Peninsular Malaysia.

Study site
This study focuses solely on Peninsular Malaysia, with emphasis on limestone karsts where the majority of study materials were obtained. Peninsular Malaysia is situated at the lower end of the Malay Peninsula, which is also politically divided into Thailand and Myanmar in the north. Peninsular Malaysia is at the centre of the Tropical East Asian region and hence shares similar fauna with South and East Asia (Corlett 2014), including the genus Alycaeus (Kobelt 1902, Egorov 2013. Peninsular Malaysia is characterised by parallel, old (circa 200 million years old) and tall (circa 1000-2000 m high) non-limestone mountain ranges aligned at a north-south axis, separating flat alluvial and knolled valleys (Paton 1961, Metcalfe 2013. Within these valleys, limestone bedrocks of various ages are occasionally exposed as disjunct or continous limestone tower karsts (Paton 1961). These tower karsts have been exposed for millions of years and have gradually become isolated from each other through weathering and erosion (Benthem Jutting 1960b, Paton 1961, Twidale 2006. As such, ecosystems on limestone karsts are well known to be analogous to island ecosystems and have high species endemism including land snails (Clements et al. 2006, Liew et al. 2014).

Literature, fieldwork and collection data management
For literature review, the term "Alycaeus" was used to obtain publications from the Zoological Record, Google Scholar and Biodiversity Heritage Library (on 15 March 2016 and 30 May 2017). All publications mentioning Alycaeus species from Peninsular Malaysia were studied and reviewed.
The management of data for examined materials follows Liew et al. (2014). Materials from BOR/MOL and ZRC were personally examined by the first author. Materials elsewhere and their associated measurements and photographs were obtained either through existing digitised museum collections or with help from curators (MNHN -Manuel Caballer and Virginie Héros, NHM -Jonathan Ablett) and visiting scientists (SMF -Páll-Gergely Barna, MNHN -Gopalasamy Reuben Clements, ANSP -Siong Kiat Tan, RMNH/ZMA -Thor-Seng Liew). The number of shells for each collection lot examined were indicated after the virgule that follows after the accession number.
The locality for each collection lot was identified and linked to its current name whenever possible. For limestone karst localities, we followed the standard format of code and name (e.g. PRK 18 Gunung Lanno) used in the limestone hill register by Liew et al. (2016). Place names in this paper contain Malay words, namely: Batu = rock; Bukit/Buket = hill; Gua = cave; Gunung/Gunong = mountain; Kota = large tower karsts or fortress; Kuala/Kwala = estuary or river confluence; Pulau = island; Sungai/Sungei = river; Tasik = lake; Wang = large doline or valley surrounded on all sides by tower karsts. Geographical coordinates for the type locality of each species was provided except when the stated type locality was not exact i.e. only state-level or island names were given as the type locality. The locality records for each species based on materials examined are shown in Figures 2, 3, 4, 5 and 6.
In addition to the previously collected museum materials, a systematic sampling of Alycaeus at 80 localities across Peninsular Malaysia was conducted in 2016 (for full list of localities, see Suppl. material 1). During the sampling, about 45 to 60 minutes were spent at each locality to search for living and dead Alycaeus individuals on all habitats (in the leaf litter, under rotten logs, on vegetation and on rocky substrates). Up to 20 individuals per species were observed and collected whenever possible. Animal colouration, habitat and other ecological observations were noted.  Table 1. Table 1. Framework for species description based on 39 shell and operculum features, as well as living animal colour. Number codes are ascribed to each character and linked to illustrations in Figure 1 for visualisation of character descriptions and measurements, except shell colour and living animal colour.

Morphological section Character
Descriptions and measurements To assist with visualising the descriptions, we provided photographs of five standard shell views (apertural, lateral, apical, umbilical and dorsal/oblique dorsal), three close-up shell views (breathing tube, apical whorls, radial rib and spiral line sculpture) and four standard operculum views (exterior, interior, side and oblique exterior) for each species. More than one specimen is illustrated for each species to represent the intraspecific variability if required. A synoptic plate of shells at apertural view representing the 23 Alycaeus taxa in Peninsular Malaysia ( Figure 31) is provided to compare shell size and shape.
We measured up to 28 shells representing the whole spectrum of variation in shell height, shell width, spire height, spire width, aperture height and aperture width for Alycaeus altispirus is not included in the maps because no specific locality was given for the materials examined (see Discussion section under the species). Note the red areas are limestone karsts (derived from Liew et al. 2016). each species to gauge intraspecific variation of shell dimensions against interspecific variation (Table 1, Figure 1). In addition to this, up to 9 shells representing the whole spectrum of shell shape and sizes for each species were measured for the number of whorls, position of whorl constriction, length of breathing tube, spiral line spacing, radial ribs spacing and peristome orientation (Table 1, Figure 1). The variations are summarised in the species description (for raw data of individual shell measurements, see Suppl. material 2). Type materials available to us were also measured. They were then assigned to respective species based on the assessment framework in Table 1. Overall, materials examined totalled 5137 specimens from 522 collection lots which is comprised of: ANSP -9 collection lots (including 1 type lot), 22 specimens in total; BOR/MOL -411 collection lots (including 48 type lots), 3031 specimens in total; MNHN -6 collection lots (including 6 type lots), 10 specimens in total; NHM -3 collection lots (including 3 type lots), 5 specimens in total; RMNH -13 collection lots (including 2 type lots), 137 specimens in total; SMF -2 collection lots (including 2 type lots), 2 specimens in total; ZMA -5 collection lots, 7 specimens in total; ZRC -73 collection lots, 1923 specimens in total.
Overall, we employed the morphological species concept in this study as our comprehensive 39 characters assessment on a large sample size enables us to understand intraspecific variation of shell dimensions against interspecific variation. In addition to this, we also follow previous studies in recognising the major role of limestone hill isolation and biogeography in vicariance and speciation of karst restricted taxa especially land snails in Peninsular Malaysia , Hoekstra and Schilthuizen 2011, Liew et al. 2014. Notably, a study of another limestone restricted genus Plectostoma inhabiting limestone hills that are near each other but separated by biogeographic barriers may only differ a little in morphology but is sufficiently genetically distinct to be considered as different species (Liew et al. 2014). Given that many of the Plectostoma species in Liew et al. (2014) were sampled from the same localities as Alycaeus in this study and that most Alycaeus species are also restricted to limestone areas, it is very likely that Alycaeus in this study will show the same trend of morphological variation and speciation as Plectostoma. To conclude, this study represents the first attempt at a systematic taxonomic review of Alycaeus species in Peninsular Malaysia and has used a large quantity of materials and characters to arrive at an empirically supported species hypothesis. The emergence of additional evidences such as genetics and anatomy in the future will be useful to further assess these species hypotheses.

Shell and operculum characters
The description of shell and operculum characters partially follows the terminology established by Godwin-Austen (1889) and Kobelt (1902). However, a revised set of 39 shell and opercular characters are introduced in this study to provide a comparative morphological framework with objective empirical data for all Alycaeus specimens that were examined in this study (Table 1, Figure 1). All measurements are in millimetres and are rounded up to the nearest 0.01 mm. Most of the characters can be observed by stereomicroscope at 2.0 × magnification except protoconch sculpture, spiral lines and radial ribs (some species) which can only be seen with at least 4.0 × magnification. Two archaic terms have also been replaced based on latest findings: (1) "horny operculum" (Godwin-Austen 1889) to proteinaceous operculum (see Checa and Jiménez-Jiménez 1998), (2) "sutural tube" (Godwin-Austen 1889) to breathing tube (see Páll-Gergely et al. 2016). Whorl constriction. Position of constriction about 2 ¼-5 ¼ whorls posterior of protoconch.
Radial ribs running anterior of breathing tube. Pronounced, indistinct or absent. Even or unevenly spaced. 6-21 radial ribs per 1 mm.
Radial ribs running perpendicular to breathing tube. Pronounced, indistinct or absent. Radial ribs sometimes are thicker and whiter compared to radial ribs anterior of breathing tube. Even or unevenly spaced. 6-29 ribs per 1 mm.
Operculum. Concave or flat. Rounded or conical. Exterior usually calcareous layered of variable thickness. Exterior texture varies (smooth, finely granulated, flaky, short calcareous spikes, cup-like projection at nucleus, scaffold-like calcareous deposits or appressed radially spiral lamellae). Interior usually proteinaceous layered. Interior sculpture smooth, with multilamellar impression or mamillated.
Shell colour. Varies between and within species (white, pinkish-white, pink, yellow, orange, red, brownish-red. brown, purple). Apical whorls either in white or nonwhite colours, always fading to white in subsequent whorls.
Living animal. Body colour variable but lighter than head and tentacle (creamwhite, yellow, cream-yellow, light brown, brown, maroon, greenish-black, light grey, grey). Head colour variable (orange, pink, pinkish-brown, brown, maroon, greenishblack, grey, dark grey). Tentacle either uni-coloured (yellow, red, brown, reddishbrown, light grey, dark grey, black), or bi-coloured (green with brown tips, creamwhite with pink tips, yellow with red tips). Head and tentacle often darker coloured relative to the body.
Habitat and ecology. Three distinct habitats: rock (crevices, rock walls, solution holes, moss and lichen covered rocks), vegetation (low shrubs, tree trunks) or forest floor (rotten logs, leaf litter). Usually in moist areas but ocassionally found in drier areas. Always in forested habitats.
Remarks. The genus Alycaeus Baird, 1850, is separated into three subgenera -Alycaeus Baird, 1850, Pincerna Preston, 1907, and Stomacosmethis Bollinger, 1918(Egorov 2013. However, all of these subgenera (including Pincerna (see Páll-Gergely 2017)) remain inadequately defined as no clear diagnostic characters have ever been identified (Godwin-Austen 1889) and hence will require extensive revision, a task that is beyond the scope of this study and will instead be treated in later studies (B. Páll-Gergely, pers. comm.). Thus, we do not provide a diagnosis for the genus Alycaeus here pending a revision of the Alycaeidae and resolution of diagnostic characters useful for supraspecific groups. Instead, consistent with our study scope, we will only provide a description of characters relevant to Peninsular Malaysian Alycaeus species.  Spire. Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, white and thicker than those anterior of breathing tube, evenly spaced. Approximately 9-15 ribs per 1 mm.

Alycaeus alticola
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and regularly spaced at the middle until prior to aperture. Approximately 7-15 ribs per 1 mm.
Shell colour. Whorls yellow, fading to white posterior of constriction. Peristome white. Living animal. Body cream-white with fine brown blotches. Head brown. Tentacles brown.
Habitat and ecology. Lives on rock surfaces covered with powdery lichen at higher and drier areas of the limestone hills, often at open places exposed to ambient sunlight. They never appear on wet and mossy sections of limestone rocks and are rarely seen in lower parts of limestone hills that are shaded by forest cover.
Distribution range. Restricted to Bukit Mengapur, Pahang. Differential diagnosis. Alycaeus alticola sp. n. varies in the degree of ultimate whorl expansion within population but has a consistently more expanded and globose whorl compared to A. costacrassa sp. n., A. selangoriensis sp. n. and A. kapayanensis. Alycaeus alticola sp. n. shares similar shell shape with Alycaeus charasensis sp. n. but differs in the presence of pronounced radial ribs and spiral lines, as well as less expanded ultimate whorl.

Discussion.
A. alticola sp. n. is among the larger yellow, conical shelled Alycaeus in Peninsular Malaysia.   Radial ribs running anterior of breathing tube. Radial ribs pronounced, evenly spaced. Approximately 8 ribs per 1 mm.

Alycaeus altispirus Möllendorff, 1902
Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, white and thicker than those anterior of breathing tube, evenly spaced. Approximately 16 ribs per 1 mm.
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and evenly spaced from the middle section until prior to aperture. Approximately 10 ribs per 1 mm.
Operculum. Unknown. Shell colour. Whorls yellow. Peristome white. Living animal. Unknown. Habitat and ecology. Unknown. Distribution range. Unknown. Appears to be restricted to Kelantan. Differential diagnosis. Alycaeus altispirus is most similar to Alycaeus regalis sp. n. in having a large shell (shell height: 6.40-7.18 mm, shell width: 5.86-6.87 mm) and tall spire (spire height: 2.32-2.90 mm) but differs in the ultimate whorl being more keeled-like, upper palatal section folded posteriorly into a wing-like structure and peristome orientated oblique to the coiling axis. Unlike Alycaeus perakensis, Alycaeus altispirus is smaller (smaller by about 0.23 mm in shell height, 0.25 mm in shell width) and has a much less expanded ultimate whorl.
Discussion. To date, this species is only known from the four type specimens collected by John Waterstradt (Möllendorff 1902, Zilch 1957 presumably from the same locality as A. kelantanensis, on Pulai Princess Cave hill (4°47'38"N, 101°56'31"E), Kelantan (see Discussion under A. kelantanensis; Waterstradt 1902, Liew et al. 2014). Yet no recent shells have been found on surveyed limestone hills near the locality (about 5 km from Pulai Princess Cave hill) or elsewhere in Kelantan. At the time of its description, Möllendorff (1902) considered A. altispirus a subspecies of A. perakensis but did not elaborate why. We disagree with this decision because the two taxa differ markedly from each other in shell shape especially the degree of expansion and shape of the ultimate whorl as well as their very disjunct distribution range. As such, we consider A. altispirus a species on its own.   Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, evenly spaced. Approximately 7-10 ribs per 1 mm.

Alycaeus balingensis Tomlin, 1948
Radial ribs running posterior of breathing tube. Radial ribs initially indistinct and dense, but increasingly becomes pronounced and evenly-spaced towards the aperture. Approximately 2-4 ribs per 1 mm.
Operculum. Concave, rounded. Exterior covered by calcareous layer, with short calcareous spikes. Interior covered by proteinaceous layer, smooth.
Shell colour. Red, yellow or white at apical whorls. All colours fade to white towards ultimate whorl.
Living animal. Body greenish-black. Head greenish-black. Tentacle green with brown tips.
Habitat and ecology. Lives in crevices on wet limestone boulders and shrubs close to the ground. In forested areas of limestone hills.
Differential diagnosis. Alycaeus balingensis shares similar shell shape (globose whorls) with Alycaeus liratulus and Alycaeus thieroti but differs in having whorls with denser and more pronounced radial ribs, absence of spiral lines, operculum exterior with short spikes and greenish-black body.
Discussion. Alycaeus balingensis is listed as Critically Endangered in the IUCN Red List as it was known only from the actively quarried Bukit Baling at the time of assessment (Clements 2009). Given that new populations have now been discovered in two other localities in Kedah and Perak, the conservation status of A. balingensis should be revised.
Radial ribs running posterior of breathing tube. Radial ribs indistinct to absent, only unevenly spaced radial growth lines present.
Shell colour. Whorls yellow to brown. Peristome white. Living animal. Unknown.
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and evenly spaced at the middle until prior to aperture. Approximately 7-19 ribs per 1 mm.
Shell colour. Whorls yellow, fading to white posterior of constriction. Peristome white.
Living animal. Body cream-white with fine brown blotches. Head brown. Tentacles brown.
Habitat and ecology. Lives on rock surfaces covered with powdery lichen at higher and drier areas of the limestone hills, often at open places exposed to ambient sunlight. They never appear on wet and mossy sections of limestone rocks and are not found in lower parts of limestone hills that are shaded by forest cover.
Distribution range. Restricted to Bukit Charas and Bukit Tenggek, eastern Pahang.
Differential diagnosis. Alycaeus charasensis sp. n. shares similar variability in shell shape with Alycaeus alticola sp. n. but consistently differs in having a larger shell, wider ultimate whorl, widely spaced spiral lines and uneven, widely spaced radial growth lines in place of radial ribs. Alycaeus charasensis sp. n. is distinguished from other tall spired, conical yellow shelled Alycaeus in Peninsular Malaysia by its lack of distinct radial ribs. Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, white and thicker than those anterior of breathing tube, evenly spaced. Approximately 11-16 radial ribs per 1 mm Radial ribs running posterior of breathing tube. Radial ribs pronounced, unevenly spaced immediately posterior of constriction, becoming pronounced and evenly spaced from the middle section until prior to aperture. Approximately 11-16 ribs per 1 mm.  Alycaeus conformis Fulton, 1902: 68-69;Sykes 1903: 198;Laidlaw 1928: 34;Laidlaw 1932: 36;Venmans 1956: 81, figure 1; Robertson et al. 1987: 2;Chan 1997   Radial ribs running perpendicular to breathing tube. Radial ribs more pronounced and thicker than those anterior of breathing tube, evenly spaced. Approximately 9-13 ribs per 1 mm.
Radial ribs running posterior of breathing tube. Ribs absent. Only radial growth lines.
Shell colour. First 3 whorls usually red or pink. All colours fade to white towards ultimate whorl.
Living animal. Body grey. Head grey. Tentacles dark grey to black. Habitat and ecology. Lives under large rotten logs and on leaf litter. In wet, shady forests in both limestone and non-limestone areas.
Differential diagnosis Alycaeus conformis is most similar to Alycaeus gibbosulus in shell shape but differs in having a less expanded penultimate whorl, finer radial ribs anterior of breathing tube, shorter constriction whorl, shorter breathing tube, less oblique peristome and multilamellated operculum exterior. The animal body is dark grey in A. conformis compared to brown in A. gibbosulus.
Discussion. Fulton (1902) stated the type locality of A. conformis as Perak without further specifying the location. Perak is a large state in western Peninsular Malaysia. During recent intensive sampling across limestone hills in Perak, Alycaeus conformis was only discovered at one locality, Gunung Rapat. Alycaeus conformis has also been reported from Kelantan (Sykes 1903, Laidlaw 1928, Selangor (Laidlaw 1932, Ven-mans 1956, Pahang and Johor. Venmans (1956) described the radular morphology of A. conformis from Batu Caves, Selangor. Páll-Gergely et al. (2016) described the microstructures associated with the breathing tube of A. conformis from Phuket Island, Thailand. The shells of A. conformis are often coated in a layer of organic matter when alive ( Figure 5E).  Radial ribs running posterior of breathing tube. Radial ribs pronounced and ueneven immediately posterior of constriction, becoming pronounced and evenly spaced towards the aperture. Approximately 10-21 ribs per 1 mm.
Shell colour. Whorls yellow, fading to white posterior of constriction. Peristome white.
Habitat and ecology. Lives on wet limestone walls covered with mosses. Occassionally found in crevices, on lower parts of tree trunks. In shady forests on limestone hills.
Distribution range. Widespread from southern Kelantan to central Pahang. Differential diagnosis. Alycaeus costacrassa sp. n. most resembles A. selangoriensis sp. n. in its thick operculum, pronounced radial ribbing and spiral lines but has a narrower ultimate whorl and a more circular peristome without posterior folding at the upper palatal section. Alycaeus costacrassa sp. n. also resembles A. kapayanensis in shell shape but differs in its consistently more pronounced radial ribs as well as operculum with thicker calcareous exterior.
Discussion. Shells of A. costacrassa sp. n. are consistent in their diagnostic characters but vary considerably in shell size and whorl convexity across its range.  Figure 15A-E) with rounded whorls. It is possible that A. costacrassa sp. n. may contain several cryptic species pending availability of molecular data for investigation.

Alycaeus expansus sp. n.
http://zoobank.org/E2003BE4-BAD9-42B9-A89D-40ABB6EACED1 Figures 7N, 16  Etymology. Latin, meaning expanded. In reference to the very expanded peristome and globose whorls. Discussion. Prior to this study, shells of A. expansus sp. n. from Bukit Charas and Bukit Panching were labelled as A. kelantanensis (BOR/MOL and ZRC collection lots). Shells of A. expansus sp. n. is consistent in its diagnostic obtuse ultimate whorl and very expanded peristome across its range but varies in shell size and spire height for each hill population. Shells from Bukit Sagu and Bukit Tenggek (the northern two of the Kuantan Hills) tend to be larger with ultimate whorl always obtused and spire low. Shells from Bukit Charas and Bukit Panching (the southern two of the Kuantan Hills) tend to be slightly smaller and more variable in ultimate whorl shape (obtuse to normal) and spire height (tall to low). It is possible that A. expansus sp. n. may contain two cryptic species pending availability of molecular data for investigation. Unfortunately, populations on Bukit Panching, Bukit Tenggek and Bukit Sagu are now likely lost to limestone quarrying (see Discussion in A. carinata). Figures 7F-G   Radial ribs running perpendicular to breathing tube. Radial ribs more pronounced and thicker than those anterior of breathing tube, evenly spaced. Approximately 8-14 ribs per 1 mm.
Operculum. Concave, conical. Exterior covered by thick calcareous layer. Exterior has scaffold-like calcareous deposits overlaid on radially spiral lamellae. Interior covered by proteinaceous layer, mamillated.
Shell colour. First 3 whorls usually red, purple or pink. All colours fade to white towards ultimate whorl.
Living animal. Body brown. Head brown. Tentacles light to dark grey. Habitat and ecology. Lives under large rotten logs or on leaf litter. In wet, shady forests in both limestone and non-limestone areas.
Distribution. Widespread from Perlis to Perak on the west coast and in parts of Kelantan and Terengganu on the east coast but not found in Selangor, Pahang and the southern states of Peninsular Malaysia. Elsewhere, in Trang, southern Thailand (as Dioryx pyramidalis (Benson, 1856), in Habe (1965)).
Differential diagnosis. Alycaeus gibbosulus is most similar to A. conformis in shell shape but differs in having a more expanded penultimate whorl, coarser sculpture, more oblique peristome, longer constriction whorl, longer breathing tube (longer by 0.66 mm), ultimate whorl that is very obtused prior to constriction and scaffold-like calcareous deposits at the operculum exterior. The animal body is brown in A. gibbosulus compared to grey in A. conformis.
Discussion. The syntypes of A. gibbosulus is housed in the Indian Museum, Kolkata, India (Nevill 1878) but was not examined in this study. Nevertheless, topotypic specimens from Penang Island (BOR/MOL 8525, BOR/MOL 8526) match the illustration of the type by Stoliczka (1872). This is considered to be sufficient for positive species identification. This species is closely related to A. conformis and has historically been confused with it. Studies that reported A. gibbosulus in various localities are as follows: Penang (Stoliczka 1872, Crosse 1879b, Tenison-Woods 1888, Kobelt 1902, Laidlaw 1928, Möllendorff 1891, Perlis (Benthem Jutting 1960a), Perak (Crosse 1879b, Möllendorff 1886, Möllendorff 1891, Davison 1995, Chan 1998b and Kelantan (Sykes 1902, Möllendorff 1902. Möllendorff (1886) reported that Perak shells differ from Penang shells in being paler as well as possessing a wider ultimate whorl. These shell forms are well within the morphological variation of A. gibbosulus. An erroneous record of Dioryx pyramidalis Benson, 1856 in Peninsular Malaysia has been traced back to a mistake by Habe (1965) in which specimens of A. gibbosulus from northern Malay Peninsula were misidentified as Alycaeus pyramidalis Benson, 1856. The species Alycaeus chaperi Morgan, 1885b, is also a synonym of Alycaeus gibbosulus (Möllendorff 1886, Möllendorff 1891. Alycaeus gibbosulus has been reported to exist sympatrically with A. conformis in Gunung Rapat, Perak (Foon et al. 2017). Elsewhere range overlaps between A. gibbosulus and A. conformis remain unresolved. In Kelantan, Sykes (1902) mentioned a collection of shells with typical A. gibbosulus characters and some which were "much less gibbous". These less gibbous shells are likely A. conformis, which is common in Kelantan. Hence, it is possible that both A. gibbosulus and A. conformis exist sympatrically in Kelantan. In Pahang where only A. conformis records are confirmed, an aberrant record of A. gibbosulus from Kuala Tahan (Benthem Jutting 1960a) warrants investigation. The shells of A. gibbosulus are sometimes coated in a layer of organic matter when alive ( Figure 7F).   Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, white and thicker than those anterior of breathing tube, evenly spaced. Approximately 13-18 ribs per 1 mm.

Alycaeus ikanensis
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and unevenly spaced towards the aperture.
Shell colour. Whorls yellow, fading to white posterior of constriction. Peristome white. Living animal. Unknown.

Habitat and ecology. Lives on limestone walls and boulders covered with mosses. In shady forests on limestone hills.
Distribution range. Restricted to Gua Ikan, central Kelantan. Differential diagnosis. Alycaeus ikanensis sp. n. is distinctive in being the smallest species among conical, yellow shelled Alycaeus species in Peninsular Malaysia. Alycaeus ikanensis sp. n. is distinguished from A. costacrassa sp. n. by its consistently much smaller shell (smaller by about 0.62 mm in shell height, 0.90 mm in shell width) and narrower ultimate whorl.
Discussion. Limestone hills adjacent to the type locality Gua Ikan may also harbour populations of the species.   Habitat and ecology. Lives on limestone rock surfaces and crevices. In wet, shady forests on limestone hills.

Alycaeus jousseaumei Morgan, 1885a
Distribution range. Restricted to the karsts of Kinta Valley, Perak. Its known northern limit is at Gunung Tchehel and southern limit at Gunung Tempurung.
Differential diagnosis. Alycaeus jousseaumei is distinguished from all other Alycaeus species in Peninsular Malaysia by its very low spire, very expanded, obtuse ultimate whorl and very expanded, double peristome with wide interspace.

Alycaeus kapayanensis Morgan, 1885b
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and evenly spaced at the middle until prior to aperture. Approximately 11-23 ribs per 1 mm.
Habitat and ecology. Lives on both dry, bare rock and wet limestone walls covered with mosses or tree roots. Although it inhabits forested areas, A. kapayanensis has also been found on revegetated limestone walls at former quarries.
Distribution range. Restricted to the karsts of Kinta Valley, Perak. Its known northern limit is at the Sungai Kerdah karst region, northeast of Sungai Siput Utara town and southern limit at Gunung Tempurung. Differential diagnosis. Alycaeus kapayanensis is similar to A. costacrassa sp. n. but differs consistently in having less pronounced spiral ribs and much thinner operculum. Alycaeus kapayanensis also resembles A. selangoriensis sp. n. but is consistently smaller shelled (smaller by about 0.96 mm in shell height, 1.6 mm in shell width), has less whorls, less expanded ultimate whorl and thinner operculum.
Discussion. Historically, many Peninsular Malaysian Alycaeus with small, yellow and conical shells were lumped under A. kapayanensis out of convenience (ZRC collection lots). We systematically and empirically examined these shells from across the peninsula and concluded that A. kapayanensis is restricted to Kinta Valley. Superficially similar species elsewhere differ consistently in shell, operculum and animal characters and are thus described as new taxa: Alycaeus costacrassa sp. n., Alycaeus selangoriensis sp. n., Alycaeus ikanensis sp. n., Alycaeus alticola sp. n. and Alycaeus charasensis sp. n. In Kinta Valley, many A. kapayanensis shells have previously been labelled as "A. perakensis var. minor", a nomen nudum (Clements et al. 2008, ZRC collection lots). The only morphological variability in A. kapayanensis is the degree of expansion of the ultimate whorl.
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and evenly spaced at the middle, absent again towards the aperture. Approximately 11-20 ribs per 1 mm.
Shell colour. Whorls white throughout. First 3 whorls occasionally yellow. Living animal. Body cream-white. Head pinkish. Tentacles yellow, with red tips. Habitat and ecology. Lives in rock crevices and limestone solution holes. In moist, shady forests. Occur on both limestone and non-limestone areas.
Distribution range. Widespread across southern Kelantan. Differential diagnosis. Alycaeus kelantanensis varies in shell size and whorl convexity but can nevertheless be distinguished from other similar sized Alycaeus by its rather angular and winged double peristome, pronounced and widely-spaced radial ribs and spiral lines, as well as the red-tipped yellow tentacles of its soft body. Alycaeus kelantanensis is similar to A. clementsi sp. n. in shell colour but differs in being consistently smaller shelled (smaller by about 2.13 mm in shell height, 2.32 mm in shell width), having smooth operculum exterior and a more angular double peristome.
Discussion. The type specimen for A. kelantanensis was collected by John Waterstradt, likely from the Pulai Princess Cave hill (4°47'38"N, 101°56'31"E), south of Gua Musang, Kelantan (after Liew et al. 2014, Waterstradt 1902. Alycaeus kelantanensis shells from across its range are consistent in their diagnostic characters but varies in shell size within and between populations. Aside from the locations listed above, this species has also been recorded from limestone hills near Kuala Betis, 25 km west of Gua Musang, Kelantan (Berry 1965) and in the non-limestone Lojing Highlands, Kelantan (Liew 2010 Radial ribs running perpendicular to breathing tube. Radial ribs pronounced and thicker than those anterior of breathing tube, evenly spaced. Approximately 9-16 ribs per 1 mm.
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction. At the middle section, becoming pronounced and evenly spaced from the middle section until prior to aperture. Approximately 10-15 ribs per 1 mm.
Habitat and ecology. Lives on both dry and wet limestone walls. In shady forests and cliffs on limestone hills.
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming distinct and unevenly spaced at the middle and then absent again prior to aperture.
Shell colour. Off white, apical whorls occasionally pinkish white. Living animal. Body maroon. Head maroon. Tentacles red or brown tipped.
Habitat and ecology. Lives on shrubs close to the ground. In forested areas of limestone hills.
Distribution. Restricted to central and southern Kelantan. Elsewhere, isolated records in northern Sumatra, Indonesia (Benthem Jutting 1959, Marwoto 2016 need to be verified. Differential diagnosis. Alycaeus liratulus is most similar to Alycaeus thieroti in shell shape but differs in having a larger shell (larger by about 1 mm in shell height, 0.8 mm in shell width), wider-spaced radial ribs and spiral lines, longer breathing tube (longer by 0.65 mm) and flat operculum with cup-shaped calcareous extension at the nucleus exterior.
Discussion. Confusion between A. liratulus and A. thieroti due to similarity in shell shape and poor original descriptions have led to many misidentifications in the past (see Discussion in Alycaeus thieroti). Isolated records of A. liratulus from northern Sumatra (Benthem Jutting 1959, Marwoto 2016 have to be re-examined. Laidlaw (1928) considers A. liratulus as closely related to the A. globosus of Borneo, an opinion we concur based on its globose shell. However, A. globosus differs from A. liratulus in the arrangement and density of radial ribs, short breathing tube and absence of a cupshaped projection at the operculum exterior.
Supraspecific classification was attempted for A. liratulus by Preston (1907), who created a new subgenus Pincerna based on the sole diagnostic character of the cupshaped protrusion on the operculum exterior of A. liratulus. However, the operculum structure is an unsuitable diagnostic character because analogous structures have also been found in Alycaeus kukenthali Sarasin & Sarasin, 1899 and Alycaeus ochraceus Godwin-Austen, 1893, two species unrelated in shell shape to A. liratulus (Sarasin and Sarasin 1899, Laidlaw 1928, Páll-Gergely 2017   Discussion. Prior to this study, specimens of A. regalis sp. n. from Gunung Senyum were always labelled as Alycaeus perakensis altispirus (Tarruella and Domènech 2011; ZRC collection lots) even though they clearly differ from each other, especially in the aperture shape. Alycaeus regalis sp. n. occur sympatrically with A. costacrassa sp. n. and A. senyumensis sp. n. although the two are separated by their habitat preferences. Alycaeus regalis sp. n. appear to prefer drier habitats whereas A. costacrassa sp. n. and A. senyumensis sp. n. are always found on wet rocks with mosses. Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, evenly spaced. Approximately 7-10 ribs per 1 mm.

Alycaues roebeleni
Radial ribs running posterior of breathing tube. Radial ribs pronounced, unevenly spaced immediately posterior of constriction.
Shell colour. Yellow at apical whorls. Either fades to white towards ultimate whorl or remain yellow throughout.
Living animal. Unknown. Habitat and ecology. Lives on limestone rock crevices covered by mosses. In shady forests on limestone hills. Distribution range. Restricted to limestone hills of the Chuping geological formation in central Perlis. Elsewhere, in Koh Samui and Phatthalung, southern Thailand (Möllendorff 1894, materials examined).
Differential diagnosis. Alycaeus roebeleni is most similar to A. perakensis in shell shape but is larger (larger by about 0.97 mm in shell height, 1.96 mm in shell width), spire taller and wider (taller by about 0.22 mm in spire height, wider by about 0.31 mm in spire width), penultimate whorl wider as well as peristome more expanded (Möllendorff 1894). Alycaeus roebeleni also differs from A. perakensis in its operculum, which has a smooth exterior and thick, brown proteinaceous layer at the interior. The spire height of A. roebeleni is quite variable across its range but never as tall as A. perakensis.
Discussion. This species was considered closely related to A. perakensis by Möllendorff (1894), which we concur with, based on examined specimens. However, contrary to the Möllendorff (1894) claim that the operculum is entirely proteinaceous, we show that A. roebeleni has proteinaceous interior and calcareous exterior layers. Despite clear distinctions made between A. roebeleni and A. perakensis in Möllendorff (1894), the two species remain confused by past workers. An A. roebeleni collection lot in ZRC was originally labelled as A. perakensis (ZRC 1975.2.22.99-126 ZRC 1975.2.22.190-228/39, ZRC 1975.2.24.403-439/37, ZRC 1997 Etymology. Named after Selangor, the state that the type locality of this species is part of. Radial ribs running perpendicular to breathing tube. Radial ribs pronounced, white and thicker than those anterior of breathing tube, evenly spaced. Approximately 11-21 ribs per 1 mm.
Radial ribs running posterior of breathing tube. Radial ribs absent immediately posterior of constriction, becoming pronounced and evenly spaced at the middle until prior to aperture. Approximately 9-14 ribs per 1 mm.
Habitat and ecology. Lives on wet limestone walls covered with mosses, in forested areas. It can also be found in areas with substantial human disturbance such as on the limestone walls of the temple at Batu Caves.
Distribution. Restricted to Batu Caves and Bukit Takun, Selangor. Differential diagnosis. Alycaeus selangoriensis sp. n. is most similar to A. kapayanensis but differs in having a consistently larger shell (larger by about 0.96 mm in shell height, 1.6 mm in shell width), more expanded ultimate whorl and thicker operculum with calcareous exterior. The upper palatal section of the peristome in A. selangoriensis sp. n. is always folded posteriorly and downwards, creating a wing-like extension prior to the notch at the suture, a feature not present in the simple circular expanded peristome of A. kapayanensis. Alycaeus selangoriensis sp. n. resembles A. perakensis in having a moderately expanded ultimate whorl but differs in being smaller shelled (smaller by about 1.37 mm in shell height, 2.08 mm in shell width).
Discussion. Historically, Alycaeus selangoriensis sp. n. shells have been assigned to superficially similar congeners A. perakensis and A. kapayanensis (Laidlaw 1932, Venmans 1956, Chan 1997. Alycaeus selangoriensis sp. n. has also been labelled as "Alycaeus kapayanensis var. minor", a nomen nudum (Clements et al. 2008, ZRC collection lots). Alycaeus selangoriensis sp. n. is morphologically consistent in having a very expanded ultimate whorl but varies in spire height. Venmans (1956) described and found that the radula and jaw of A. selangoriensis sp. n. differ substantially from A. thieroti and A. conformis. Differential diagnosis. Alycaeus senyumensis sp. n. is distinguished from other Alycaeus by its peristome that is distinctly expanded and angled at the columellar section and partially obscuring the umbilicus, narrow ultimate whorl, strong radial ribs, shallow suture and small shell. Alycaeus senyumensis sp. n. is differentiated from the sympatric A. regalis sp. n. and A. costacrassa sp. n. by its much smaller shell and expanded peristome angled at the columellar base.
Radial ribs running posterior of breathing tube. Radial ribs pronounced, unevenly spaced throughout.
Operculum. Concave, rounded. Exterior calcareous layer thick, smooth and polished. Exterior nucleus punctured through, with a cup-like projection. Four concentric ridges were distributed in the tunnel within the thick, cup-like projection. Interior calcareous, with dense concentric circles of multimellae, nucleus punctured through. Operculum edge teethed, etched with regularly spaced grooves.
Shell colour. Whorls yellow. Peristome white.  Differential diagnsosis. Alycaeus virgogravida sp. n. is similar to A. kapayanensis in having a conical shell but is distinguished by its more expanded whorls, spacing of radial and spiral ribs, and notably, the thick, calcareous operculum with cup-shaped nucleus. Alycaeus virgogravida sp. n. is distinguished from the globose-shelled Alycaeus liratulus, the only other species in Peninsular Malaysia with cup-shaped operculum nucleus, by its conical shell.
Discussion. Alycaeus virgogravida sp. n. is the only small, conical and yellow Alycaeus species in Peninsular Malaysia with cup-shaped operculum.