A new soil centipede from South-East Asia with a unique arrangement of ventral glands, and a revised synopsis of Gonibregmatidae (Chilopoda, Geophilomorpha)

Abstract A new gonibregmatid centipede, Vinaphilusunicusgen. n., sp. n., is described based on two females from a single location in northern Vietnam. The new genus and species are distinguished mainly by the arrangement of the ventral pore-fields, which is unique among all Chilopoda. A critically revised synopsis of the Gonibregmatidae is also given. In particular, three species are provisionally recognized in Himatosoma Pocock, 1891: H.bidivisum Silvestri, 1919, H.porosum Pocock, 1891 (= H.typicumtridivisum Silvestri, 1919, syn. n.), and H.typicum Pocock, 1891. The genera Dschangelophilus Verhoeff, 1937 and Tweediphilus Verhoeff, 1937, with their species D.coloratus Verhoeff, 1937 and T.malaccanus Verhoeff, 1937, are moved to the Gonibregmatidae, whereas Geoporophilusaporus Attems, 1930 is moved to the Oryidae as Orphnaeusaporus (Attems, 1930), comb. n.


Introduction
Gonibregmatids are frequent members of the centipede communities inhabiting the soils throughout southern Asia (Lewis 1981, Bonato andZapparoli 2011). They are among the largest and most elongated geophilomorphs, often more than 10 cm long when adults (Bonato 2011). Because of their conspicuous body size, gonibregmatids were among the first centipedes reported from tropical regions (since Newport 1843a, 1843b). Nevertheless, they are still one of the least known centipede groups, even with regards to morphology and species diversity. Moreover, they have been one of the first lineages of geophilomorphs to be distinguished at the family level (Cook 1896), yet researchers are still far from reaching a consensus on the circumscription and diagnosis of Gonibregmatidae (compare e.g. Attems 1929;Bonato 2011;Bonato et al. 2014).
Until now, less than 20 species have been referred to Gonibregmatidae, almost all of them from southern Asia (see Appendix). Most species belong to three morphologically well characterised genera: Eucratonyx Pocock, 1899, the best-known genus, with two species; Gonibregmatus Newport, 1843, comprising six poorly described and rarely recorded species, of which four are from southern Asia; Himantosoma Pocock, 1891, for which up to four nominal taxa have been distinguished and illustrated. A few other incompletely described species of gonibregmatids have been separated in other nominal genera: Disargus Cook, 1896, Geoporophilus Silvestri, 1919, and Sogophagus Chamberlin, 1912 Recent field sampling in northern Vietnam allowed us to discover a new species that adds significantly to the known morphological diversity of Gonibregmatidae and of Chilopoda as a whole, especially for the unprecedented arrangement of the pores of the sternal glands. The peculiar morphological features of the new species are here described, and its taxonomic position is discussed in the framework of an updated synopsis of the Gonibregmatidae.

Methods
Specimens were collected by manual search and fixed in 70% ethanol. Morphological examination was performed with a stereoscopic microscope (Leica MZ 125) with magnifications 8-100× and with a biological microscope (Leica DMLB) with magnifications 100-400×, by means of temporary mounts in ethylene glycol and also after dissection of the head and the mouth parts (Pereira 2000). Light photographs were taken with digital cameras applied to the two microscopes (Leica EC3 and DFC420, respectively). Line drawings were drawn from the digital photos. For the morphological description, we followed the standard terminology for centipedes as defined in Bonato et al. (2010).
In order to evaluate the taxonomic position of the new species, we browsed the primary taxonomic and faunistic literature to collate all available morphological information and geographical records for all species either referred or possibly related to Gonibregmatidae. Morphological data were critically revised, and published records were re-interpreted providing modern geographical names.

Results
Two specimens were found as representatives of a new species of Gonibregmatidae, which deserves to be distinguished in a new genus. It is described below as Vinaphilus unicus gen. n. sp. n.
Vinaphilus gen. n. http://zoobank.org/6BD441E1-3AB8-47FB-BD63-B6DA3717C02E Diagnosis. Geophilomorpha differing from all other known genera for the combination of the following characters: both anterior and posterior ends relatively stout; head and forcipular segment quite short; all appendages relatively short; club-like sensilla on multiple distal antennal articles; labrum with broad mid-part separating the lateral pieces; labral margin slightly concave and fringed with elongate, pointed projections; mandible with a single row of many short teeth; telopodite of second maxillae composed of three articles and bearing a claw provided with two marginal rows of thin projections; forcipular tergite wider than long, and as wide as the head; forcipules without denticles; no paratergites; all walking legs with similar claws; sternites with pore-fields, including two paired anterior fields and a single medial posterior field; ultimate legbearing segment with entire pleuropretergite; coxal organs opening separately through many pores, most of which aggregated on the meso-ventral side; legs of the ultimate pair much longer than those of the penultimate pair, with two tarsal articles and without claw; female gonopods basally touching, short and non-articulate.
The main diagnostic differences between Vinaphilus gen. n. and the other genera of Gonibregmatidae from Asia are summarized in Table 1 and discussed below in Discussion.
Type species. Vinaphilus unicus sp. n. Diagnosis. A Vinaphilus species with the following characters: body length up to > 8 cm; head about as long as wide, lacking transverse suture; antenna about 3 times as long as the head, with intermediate articles about as long as wide; most clypeal setae located in a broad subtriangular medial area, a few other setae close to the mid-point of the anterior margin and in 2 anterolateral groups; intermediate labral projections darker, shorter and closer to each other than lateral projections; forcipular coxosternite > 1.5 times as wide as long, with incomplete chitin-lines; trochanteroprefemur much wider than long; tarsungulum ca 2 times as long as the trochanteroprefemur, with finely serrate internal margin; poison calyx elongated; trunk tergites and sternites wider than long; around 109 pairs of legs, with 2 accessory spines; paired pore-fields of the sternites gradually changing from circular to longitudinally elongated along the trunk, but missing on the first and the prepenultimate leg-bearing segment; medial porefield of the sternites subcircular, present also on the first and the prepenultimate legbearing segment; most of the coxal pores covered by the metasternite of the ultimate leg-bearing segment, a few anterior pores on the lateral side of coxopleuron and a single posterior pore isolated on the ventral side; metasternite of the ultimate leg-bearing segment subtrapezoidal, wider than long; ultimate telopodite ca 2 times as long as the penultimate, with a small terminal spine.
Name derivation. A Latin adjective "unicus", to emphasize the unique arrangement of the ventral glandular pores. (Fig. 1A-C). Body 65 mm long, depressed, almost uniformly wide along the trunk (ca 1.3 mm) but slightly narrowing posteriorly (penultimate leg-bearing segment 0.8 mm wide). Color (in ethanol) uniformly light yellow, but head and forcipular segment slightly darker.

Description of holotype. General features
Cephalic capsule ( Fig. 2A, B). Cephalic plate sub-heptagonal, about as long as wide, lateral margins more distinctly converging anteriorly than posteriorly, posterior margin straight; scutes approximately isometric and up to ca 10 μm; transverse suture absent; setae up to ca 100 μm long. Clypeus ca 2.7 times as wide as long, with lateral margins complete; uniformly areolate, with scutes ca 10 μm wide; no obvious clypeal areas; at least 56 setae, all in the anterior half of the clypeus, most of them in a subtriangular intermediate broad area, ca 9 setae in each of 2 anterolateral smaller areas, and a few other apparently broken setae close to the mid-point of the anterior margin of the clypeus. Pleurites uniformly areolate, with 15-17 setae each. Labral margin slightly concave, with a row of 30 projections, including 8 intermediate denticles that are darker, shorter and closer to each other than the lateral projections.
Antenna (Fig. 1A, B). 14 articles. Entire antenna ca 2.7 times as long as the head width. Intermediate articles about as long as wide. Article XIV ca 2.1 times as long as wide, ca 1.6 times as long as article XIII, and twice the length of intermediate articles.
Setae gradually denser from article I to X on the dorsal side, from article I to V on the ventral side, almost completely missing on the ventral-internal side of articles I-V, however uniformly dense in the remaining distal articles. Setae gradually shorter from article I to about V, up to 100 μm long on article I and < 40 μm long on article XIV. Apical sensilla ca 10 μm long, spear-like, without projections, distinctly narrowing at about the mid-length. Club-like sensilla ca 10 μm long, grouped on the distal parts of the internal sides of articles IX-XIV and on the distal parts of the external sides of articles V-XIV. Three longitudinal rows of 1-5 proprioceptive spine-like sensilla at the bases of the antennal articles, approximately dorsal, ventro-internal and ventroexternal; rows reduced to 0-1 spine on antennal articles VI, X and XIV. A few sensilla, similar to the apical ones but slightly darker and shorter, up to 5 μm long, on both dorso-external and ventro-internal position, close to the distal margin of articles II, V, IX and XIII.
First maxillae (Fig. 3A). Coxosternite entire, with setae close to the anterior margin; a pair of lappets, covered with scales. Coxal projection subtriangular, longer than wide, with setae on the ventral side. Telopodite longer than wide, of 2 articles, with setae on the ventral side; a lappet emerging from the basal article and covered with scales.
Second maxillae (Fig. 3B). Coxosternite entire, with anterior margin deeply angulated, metameric pores on the central part of each half and about 7 setae near each of the posterior corners. Telopodite of 3 articles, slightly narrowing towards the tip; a number of setae on each article, most of them on the meso-ventral side; pretarsus ca 0.4 times as long as the distal article, slightly bent, narrowing and slightly spoon-shaped at the tip, with 7 filaments along the dorsal edge and 7 filaments along the ventral edge; 4 pore-like sensilla on each pretarsus, 1 on the convex side, 3 on the concave side.
Forcipular segment ( Fig. 2A, E). Tergite subtrapezoidal, ca 2.8 times as wide as long, with lateral margins strongly converging anteriorly, approximately as wide as the cephalic plate and ca 0.9 times as wide as the following tergite. Exposed part of the coxosternite ca 1.6 times as wide as long; anterior margin with a shallow medial concavity and without denticles; complete coxopleural sutures, entirely ventral, sinuous and diverging anteriorly; chitin-lines incomplete, only visible in the posterior part of the coxosternite. Basal distance between the forcipules ca 0.4-0.5 times of the maximum width of the coxosternite. Trochanteroprefemur ca 1.4 times as wide as long. Intermediate articles distinct. No denticles along the forcipule. Tarsungulum ca 2.8 times as long as wide, ca 2.2 times as long as the trochanteroprefemur; both the external and the internal margins uniformly curved, except for a moderate mesal basal bulge; ungulum not distinctly flattened, internal margin serrated with ca 40 small notches. Elongated poison calyx, ca 5-6 times as long as wide, lodged inside the intermediate forcipular articles.
Leg-bearing segments (Figs 1, 3C, 4). A total of 109 pairs of legs. Metatergite 1 slightly wider than the subsequent one, without pretergite. No paratergites. Walking legs shorter than the width of the trunk; legs of the first pair slightly smaller than the following ones; claws simple, uniformly bent, with 2 accessory spines, the anterior spine reaching at most 20% of the length of the claw, the posterior spine much shorter. Metasternites ca 2 times as wide as long in the anterior part of trunk, up to 1.3 times as wide as long in the posterior part. Ventral glandular pores densely grouped into 3 separate fields on each metasternite, from the second to the prepenultimate leg-bearing segments: 2 paired fields in the anterior part of the metasternite, close to the lateral margins, subcircular and closer to the anterior corners in the most anterior segments longitudinally slightly elongated and closer to mid-length along the remaining trunk; 1 subcircular medial field approximately in the centre of the metasternite in the anterior part of the body, gradually becoming closer to the posterior margin in the most posterior segments. Only the medial field on the first and the penultimate leg-bearing segment. Ultimate leg-bearing segment (Figs 1C, 3D). Pleuropretergite entire, without sulci. Metatergite subtrapezoidal, ca 1.2 times as wide as long, lateral margins convex and converging posteriorly, posterior margin slightly curved. Coxopleuron ca 1.5 times as long as the metasternite. Coxal organs of each coxopleuron opening through about 30 independent pores, mostly clustered and covered by the metasternite, but 2 or 3 pores on the lateral side of the coxopleuron, including 1 pore on the posterior third of the ventral side of the coxopleuron. Metasternite subtrapezoidal, wider than long, anteriorly ca 2.6 times as wide as posteriorly, lateral margins slightly convex and converging backwards; setae denser on 2 broad lateral parts of metasternite, almost absent close to the posterior margin and in a narrower mid-longitudinal stripe. Telopodite approximately 11 times as long as wide, ca 1.8 times as long and ca 1.8 times as wide as the penultimate telopodite; 6 articles; tarsus 2, ca 2.7 times as long as wide and ca 0.7 times as long as tarsus 1; uniformly dense setae, < 45 μm long, on most of the ventral and dorsal sides of the telopodite. Pretarsus absent, a small spine in its place.
Postpedal segments (Fig. 3D). Two gonopods, basally touching, subtriangular, without traces of articulation, covered with setae. Anal organs apparently absent. Main differences of paratype. Entire antenna ca 2.9 times as long as the head width; intermediate articles ca 1.1 times as long as wide; article XIV ca 2.0 times as long as wide and ca 1.5 times as long as article XIII. Exposed part of the forcipular coxosternite ca 1.7 times as wide as long; tarsungulum ca 1.8 times as long as the trochanteroprefemur. Metasternites ca 3 times as wide as long in the anterior part of trunk, up to 1.4 times as wide as long in the posterior part. About 40 coxal pores on each coxopleuron. Telopodite of the ultimate pair of legs approximately 13 times as long as wide, ca 2.3 times as long and ca 1.4 times as wide as the penultimate telopodite.

Taxonomic position
Considering the most recent comprehensive classification of Geophilomorpha (Bonato 2011) and an even more recent tentative reassessment after a phylogenetic analysis (Bonato et al. 2014), the new species described here is confidently recognisable as belonging to the Geophiloidea. This is especially indicated by the unilamellate shape of the mandibles, which is regarded as a major synapomorphy of the superfamily (Bonato et al. 2014).
More precisely, the structure of the labral sclerites, the shape of the labral marginal projections, the presence of filaments on the second maxillary pretarsi and the structure of the female gonopods of the new species are all plesiomorphic characters within the Geophiloidea and are common to all clades basal to the Geophilidae s.l. (Bonato et al. 2014). However, the family-level taxonomy of the basal geophiloids is still uncertain, especially with regards to the taxonomic circumscription of the traditionally recognized family Gonibregmatidae and the recently established Zelanophilidae (Crabill 1963a(Crabill , 1963bBonato 2011;Bonato et al. 2014: table S2). When considering the elongation of the head and the forcipular apparatus, details of the labrum, and the number of legs, the new species is more similar to the species of Gonibregmatus and other gonibregmatids such as Himantosoma and Geoporophilus than to the species of Zelanophilus Chamberlin, 1920 and the related Tasmanophilus Chamberlin, 1920. While the above mentioned gonibregmatids have stout head, poorly distinct labral sclerites, short and non-denticulate forcipules and more than 90 pairs of legs (Pocock 1899;Silvestri 1919;Attems 1930), the zelanophilids have slightly elongated head, distinct labral sclerites, usually denticulate forcipules and less than 90 pairs of legs (Archey 1922;Crabill 1963aCrabill , 1963b. Worth noting is that the geographical provenance of the new species (north-eastern part of the Indochinese peninsula) is well within the distribution range of the above mentioned gonibregmatids (from the Indian peninsula, through the Indochinese peninsula, the Malay Archipelago and New Guinea, to the Fijian islands; see Appendix), whereas zelanophilids have been reported so far only from Australia, Tasmania, and New Zealand (Bonato 2011, Bonato et al. 2014. Considering all gonibregmatids so far reported from Asia, including nominal species here recognized for the first time in Gonibregmatidae (see Appendix), we can conclude that the new species differs in at least some major characters that are regarded of high diagnostic value at the species level (Table 2).
Similarly, with regard to all previously described genera of Asiatic gonibregmatids, including synonyms and other uncertain gonibregmatids (see Appendix), the new species departs from the morphology of all their type species, as well as from the range of variation among the congeneric species, in some major anatomical characters that are commonly considered diagnostic at the genus level (Table 1). The new species does not fit any other genus especially for the unique arrangement of ventral pore-fields (see below) and the unusual arrangement of the coxal pores. Actually, the distribution of the coxal pores somehow resembles the condition found in all species of Himantosoma and Disargus and in the type species of Geoporophilus. In the three latter genera, however, the pores are aggregated on both the meso-ventral and the meso-dorsal sides, and are hardly covered by the adjacent metasternite, which is relatively smaller in comparison with the coxopleura (Pocock 1890;Silvestri 1919).
The new species departs also from all other genera of basal geophiloids inhabiting other continents. In detail, it differs from Madageophilus Lawrence, 1960 (a single species from Madagascar, recently referred to Gonibregmatidae; Appendix) in the elongation of the head, the arrangement of the ventral pore-fields and the absence of claws on the ultimate legs (cf. Lawrence 1960). It differs from Australiophilus Verhoeff, 1925 Crabill 1963a;Bonato 2011;Bonato et al. 2014) in the general structure of the labrum, the arrangement of the ventral porefields and the coxal pores, and the absence of claws on the ultimate legs (cf. Verhoeff 1925;Crabill 1963a). It differs also from the American genera traditionally separated in the families Eriphantidae (Eriphantes Crabill, 1970) and Neogeophilidae (Neogeophilus Silvestri, 1918 andEvallogeophilus Silvestri, 1918), which have been recently hypothesised to be strictly related to Gonibregmatidae s.s. (Bonato et al. 2014). In particular, the new species differs from Eriphantes especially in the general structure of the labrum and the forcipules, the shape of the second maxillae and the arrangement of the ventral pore-fields (cf. Crabill 1970), whereas it differs from the Neogeophilidae in the general body shape and the structure of the first maxillae and the ultimate legs (cf. Silvestri 1918;Crabill 1961).

Arrangement of sternal glands
As far as known, Vinaphilus unicus gen. n. sp. n. is unique among all other gonibregmatids, as well as all centipedes at large, in the arrangement of the ventral pore-fields (Figs 3C, 4). Ventral glands secreting sticky material are present along the body trunk in most of the geophilomorph centipedes. These glands open through the cuticle of almost all metasternites and often also on the coxae of the adjacent walking legs. The functions of the secretions are largely unknown, but are expected to have a role in deterring predators (Minelli 2011). The arrangement of the glands and the associated pores along the body is conveniently described as a modular longitudinal pattern: all or most glandular pores are grouped in one or more distinct clusters (pore-fields) on the ventral side of each leg-bearing segments. Extent, shape and position of the pore-fields are similar between adjacent leg-bearing segments, with some gradual variation across the longitudinal series of segments. The pattern of pore-fields is highly variable between species and is known to have been highly evolvable in the geophilomorph subclade Adesmata (Turcato et al. 1995).
The particular arrangement of pore-fields in Vinaphilus unicus gen. n. sp. (two sublateral paired fields anterior to a single narrow medial field; Fig. 3C) only partially resembles those found in some other gonibregmatids and some geophilids, where distinct anterior and posterior pore-fields may co-occur in single sternites. However, two anterior sublateral paired fields are never associated with a posterior single narrow medial field, rather with either a transverse very broad field (e.g. Eucratonyx; Ribaut 1912;Attems 1929) or two paired fields (e.g. Geoporophilus; Silvestri 1919). On the other hand, a posterior single narrow medial field is never associated with two anterior sublateral paired fields, rather with another single narrow medial field (Eriphantes; Crabill 1970 (Verhoeff 1937). Taxonomic notes -The species was originally classified in Geophilidae in a distinct monotypic genus Dschangelophilus Verhoeff, 1937. It was suspected to belong to Zelanophilidae by Bonato et al. (2014). It is here confidently recognised in Gonibregmatidae for the first time, based on the following characters that were described and/or illustrated by Verhoeff (1937): stout head, presence of filaments on the second maxillary pretarsi, short and non-denticulate forcipules, separate female gonopods.
Even though the mandible was described by Attems (1930) as bearing a single pectinate lamella (as found in Gonibregmatidae, but not in Oryidae), many other characters (shape of labrum, structure of first maxillae, shape of ultimate leg-bearing segment, absence of coxal pores) are common to the Oryidae, and especially to the genus Orphnaeus Meinert, 1870, and not to Gonibregmatidae. As a consequence, we propose to recognise Geoporophilus aporus Attems, 1930 as a provisionally valid species in the genus Orphnaeus, with the name Orphnaeus aporus (Attems, 1930) comb. n.

Himantosoma bidivisum Silvestri, 1919
Original description -Silvestri 1919: 101, fig. 37, as Himantosoma typicum var. bidivisa. Other sources for morphology -none. Reported specimens -1. Type locality -"Barkul" [India]. Geographical records -India: Barkul, in Odisha (Silvestri 1919). Taxonomic notes -This species was originally described as a variety of Himantosoma typicum Pocock, 1891by Silvestri (1919. It was later cited as a subspecies of H. porosum Pocock, 1891by Attems (1938, 1953 and it was recently listed at the species rank by Tran et al. (2013) but without comments. We maintain it provisionally as a separate species for consistency with the common taxonomic practice in Gonibregmatidae, because of obvious morphological differences from both H. typicum (shape of ventral pore-fields and arrangement of coxal pores, when controlling for body size) and H. porosum (number of legs, shape of ventral porefields and arrangement of coxal pores  (Attems 1938(Attems , 1953 or H. typicum (Wang 1967 (Kemp 1924;Silvestri 1924 (Verhoeff 1937); Telom Valley, near Gunung Siku, in Peninsular Malaysia (Verhoeff 1937). Taxonomic notes -The species was originally classified in Geophilidae in a distinct monotypic genus Tweediphilus Verhoeff, 1937 and its taxonomic position was never discussed subsequently. It is here confidently recognised in Gonibregmatidae for the first time, based on the following characters that were described and/ or illustrated by Verhoeff (1937Verhoeff ( , 1941: stout head, weakly defined labrum with elongate projections, presence of filaments on the second maxillary pretarsi, short and non-denticulate forcipules, separate female gonopods.

Species possibly belonging to Gonibregmatidae
Species are indicated with the name currently in use.
Other sources for morphology -none. Reported specimens -≥2. Type locality -"Luang Prabang" [=Louangphabang, Laos]. Geographical records -Laos: Louangphabang (Attems 1953). Taxonomic notes -The species was originally classified in Geophilidae in a distinct monotypic genus Luangana Attems, 1953, but it was suspected to belong to Goni-bregmatidae by Bonato et al. (2016). Its taxonomic position cannot be resolved based on the description and illustrations provided by Attems (1953). Actually, the original description was published posthumously and may be suspected to be actually composite, i.e. based on specimens belonging to different species, as suggested by the very different numbers of legs reported for the type specimens (55 and 73 pairs of legs).
In particular, the shape of the labrum, of the second maxillary pretarsi and of the pore-fields are suggestive of Gonibregmatidae, however the elongation of the head would be unprecedented for the family.