A review of the millipede genus Sinocallipus Zhang, 1993 (Diplopoda, Callipodida, Sinocallipodidae), with notes on gonopods monotony vs. peripheral diversity in millipedes

Abstract The millipede genus Sinocallipus is reviewed, with four new cave-dwelling species, Sinocallipus catba, Sinocallipus deharvengi, Sinocallipus jaegeri and Sinocallipus steineri, being described from caves in Laos and Vietnam. With the new records the number of species in the genus reaches six and the genus range is extended to Central Vietnam and North and Central Laos. Both, Sinocallipus jaegeri from Khammouan Province in Laos and Sinocallipus simplipodicus Zhang, 1993 from Yunnan, China, show high level of reduction of eyes, which has not been recorded in other Callipodida. Peripheral characters such as the relative lengths of antennomeres, the number of ocelli, the number of pleurotergites or even the shape of paraprocts and the coloration seem to provide more information for the distinction of the species than do the relatively uniform gonopods. The differences in gonopods mainly concern the shape and length of cannula, the length and shape of coxal processes g and k, and the number of the acicular projections of the femoroid. An explanation is offered for the function of the trochanteral lobe of 9th leg-pair. It provides mechanical support for the cannula and seems to assist sperm charge and insemination during copulation. An identification key to the species in the genus is produced to accommodate the new species. The new species descriptions were automatically exported at the time of publication to a wiki (www.species-id.net) through a specially designed software tool, the Pensoft Wiki Convertor (PWC), implemented here for the first time together with a newly proposed citation mechanism for simultaneous journal/wiki publications.


Introduction
Callipodidans are still poorly documented in Southeast Asia, with only 15 species, four genera and three families being hitherto known in the region (Stoev et al. 2008). Th e family Paracortinidae Wang & Zhang, 1993 is richest in species and includes two genera, Paracortina Zhang, 1993 andAngulifemur Zhang, 1997, and 12 species ranging from the southern Chinese provinces Yunnan, Sichuan and Tibet in the North to the provinces Th anh Hoa and Hoa Binh in Vietnam to the South (Wang and Zhang 1993, Zhang 1997, Shear 2000, Stoev and Geoff roy 2004, Stoev et al. 2008. Being very obscurely diagnosed, Angulifemur will most likely be synonymised with Paracortina when types are re-examined and further materials become available for study (Stoev et al. 2008).
Th e family Caspiopetalidae Lohmander, 1931, which comprises eight species distributed mainly in Central Asia, south to Punjab in Pakistan, is known in Southeast Asia with only a single cave-dwelling species, Bollmania beroni Stoev & Enghoff , 2005, from Yan Dong Cave in Yunnan (Stoev and Enghoff 2005). Th e locality lies nearly 2500 km southeast from the nearest species, B. kohalana (Attems, 1936) from Pakistan.
Th e third family, Sinocallipodidae Zhang, 1993, which is the only callipodid family entirely confi ned to the tropics, is considered to be the most primitive of all callipodidans and is placed in its own suborder, Sinocallipodidea (Shear 2000, Shear et al. 2003. Until now only two species of Sinocallipodidae have been described: Sinocallipus simplipodicus Zhang, 1993 from Xiao Cave in China, and S. thai Stoev, Enghoff , Panha & Fuangarworn, 2007 from the surroundings of Sri Wilai Temple, Saraburi Province, Th ailand (Zhang 1993, Stoev et al. 2007. Specimens provisionally assigned to S. simplipodicus were recorded also from northern Vietnam (Enghoff et al. 2004) and southern Laos (Shear et al. 2003).
Th e biospeleological explorations of Dr Louis Deharveng and Mrs Anne Bedos (Muséum National d'Histoire Naturelle, Paris, hereafter MNHN) in caves in Vietnam, and the active collecting work of Dr Peter Jäger (Forschungsinstitut und Naturmuseum Senckenberg, Frankfurt, hereafter SMF) and Mr Helmut Steiner (Hanau, Germany) in Laos revealed new material of Callipodida which was kindly off ered to us for study. All examined specimens turned out to belong to new species of Sinocallipus, which are described and illustrated below. In the paper we also comment on the gonopod shape in Sinocallipus and on some previously overlooked somatic characters, as well as the function of the trochanteral lobe on the 9 th leg-pair -a structure lacking analogues in other callipodidans -in copulation. To facilitate the identifi cation and better diff erentiation of the new taxa we also provide a key for their identifi cation.

Material and methods
All material treated in the paper is preserved in 70% ethanol and is shared between the MNHN, SMF and the National Museum of Natural History, Sofi a (NMNHS). All photographs were taken with a Leica DFC 420 digital camera mounted on a Leica MZ16A stereomicroscope. Automontage Pro software from Syncroscopy was used for image-stacking 3D focus expansion. Drawings were made with the aid of a camera lucida mounted on Leica-WILD M10 and Leica-MZ16 microscopes. All illustrations were processed and additionally cleaned up with Adobe Photoshop CS.
All species descriptions are automatically exported at the time of publication to a wiki platform (www.species-id.net) through a specially designed software tool, the Pensoft Wiki Convertor (PWC), implemented here for the fi rst time and described in this issue of ZooKeys (Penev et al. 2011). Th e link to each taxon's wiki page is published in the paper, and vice versa, the citation of the original description is present on the top of the wiki page. Th e wiki environment allows a constant update of new information on the particular taxon. Th e citation of the wiki page includes always the original description of the taxon, along with the version number, date of creation and list of the contributors to the versioned wiki page.

Description of locality.
Th is species was found in two moderately long, humid caves. Tien Duc is approximately 100 m long, while Hoa Cuong is 100-120 m long. In Tien Duc, the specimen was found on non-humid walls. Both caves host a rich cave fauna, including unidentifi ed cambalopsid and haplodesmid millipedes (L. Deharveng, in lit.).
Origin of name. For Cat Ba Island, the type locality. Diagnosis. Diff ers from S. simplipodicus, S. jaegeri and S. thai by the white-yellowish body colour, brown antennomeres 2-5 and eye composed of 33 ocelli, and from S. deharvengi by the smaller body size, antennae and gonocoxal process g, as well as by having paraprocts divided into larger ventral and smaller dorsal sclerites.
All legs white-yellowish, long and slender, ending with a long claw. Tarsal pads very poorly developed, present on leg-pairs 3-12. No particular modifi cations on coxae of pregonopodal legs, prefemora of legs 4-7 swollen. Leg-pair 9 (Figs 4, 26): coxa subtrapezoidal; trochanter expanded medio-ventrad forming a rather elongated process (h) with a pointed tip and a smaller process z.
Female: unknown. Description of locality. Th e species was found in several caves of moderate length (Hong Ruc about 50 m, Troc and Cha Noi more than 200 m), which seem to have never been surveyed previously. A road was built inside Hang Cha Noi during the War, and remains of rusted ammunitions were observed inside the cave at the time of collection. A rich cave fauna was found inside the Grotte de Troc, including two other species of Diplopoda, an undescribed cambalopsid, and Eutrichodesmus asteroides Golovatch et al., 2009 (Haplodesmidae) (Golovatch et al. 2009). All specimens were collected in the aphotic zone of the caves (L. Deharveng, in lit.).
Origin of name. Named after the French zoologist Louis Deharveng, a passionate explorer of the caves of southeastern Asia, who together with A. Bedos collected this species.
Diagnosis. Diff ers from congeners by having almost equally subdivided paraprocts, long antennae, strongly swollen and long gonocoxal process g, and comparatively short, pointed tip of the trochanteral process of leg 9. It can be distinguished from S. simplipodicus, S. jaegeri and S. thai also by the white-yellowish body colour and brown antennomeres 2-5, and from S. catba and S. steineri by the large body size.
Chaetotaxy: unknown, all setae broken off . Gonopods (Fig. 11): similar to those of congeners; diff er by the large coxal (cx) process g more than 3 times the length of process k; processes g and k apically rounded, not truncated as in S. jaegeri. Femoroid (fe): with three slender, acicular (n), and one short and subfalcate (m) terminal projections. Cannula (ca): long and slender, not coiled.
Females: 70-74 PT + telson; body colour darker, lateral sides light brownish; crests more pronounced than in males; second leg-pair unmodifi ed (Fig. 12).  Description of locality. Th ree of the adult specimens were found in a cave situated at the foot of a limestone hill overgrown with sparse vegetation (Fig. 13). Th ey were collected in the aphotic zone of the cave, somewhere between 30 and 80 m from the entrance. Th e cave is at least 100 m long, wet, with dripping water and mud on the fl oor and partly on the cave walls. In the cave S. jaegeri coexists with Heteropoda maxima Jäger, 2001 and Sinopoda sp. (Araneae: Sparassidae), Th ereuopoda longicornis (Fabricius, 1793) (Chilopoda: Scutigeridae), and cave crickets (cf. Jäger 2007). One specimen was collected outside the cave, probably under stones close to the limestone hill, approx. 2 km SW of it where the other specimens were found. Diagnosis. Diff ers from congeners by the following set of characters: reduced eyes, composed of 10-11 ocelli; well expressed, narrow, pleurotergal crests; 59-61 PT; white-yellowish body and antennae; gonopods: process g short, almost half length of that of S. deharvengi, apically truncated; k small and more abrupt apically than those of S. simplipodicus, S. thai and S. deharvengi; cannula straight.
Width of PT: 2-4<1=5<6<7<8<9<10. PT higher than broad, ratio: 1.06 : 1. Dorsal side of collum and PT 2-3 smooth; complete crests series appearing from PT 4 onwards. Crests at midbody PT well apart from each other; 6+6 (lateralmost one less pronounced), no secondary crest series, all crests well expressed (ribbed), narrow, equally broad along the whole length of metazonite, not touching anteriorly (Fig. 16). Ozopores situated on midbody PT between crests 3 and 4, visible from sixth to last but two PT. Paraprocts divided into smaller dorsal and bigger ventral sclerites. Each dorsal sclerite with a pair of macrosetae situated on small lobes in vertical line. Spinnerets: long and slender, ending with a long seta each. All setae on telson dark brown, contrasting with the white background.
Chaetotaxy (Table 1): all setae slender and apically pointed, in anterior position on all segments (excluding penultimate ones).
Gonopods (Figs 18,19): similar to those of congeners. Coxae (cx): process g short, almost half length of that of S. deharvengi, apically truncated (in lateral view); k small and more abrupt apically than in S. simplipodicus, S. thai and S. deharvengi. Femoroid (fe): with two slender, acicular (n), and one shorter and subfalcate (m) terminal projections, latter projecting into a long and thin fi lament. Cannula (ca): long and slender, not coiled.
Females: 58-59 PT in adults; middle PT slightly broader than those of the male. Remarks. Although callipodidans are often found in caves, especially in Southeast Asia and southern Europe, there are no species among them possessing an eye reduction similar to that observed in S. jaegeri and S. simplipodicus. Other peripheral characters, such as the elongated antennae and legs, in addition to the apparent depigmentation, also indicate their adaptation to the underground environment. A specimen of S. jaegeri was found also outside caves, perhaps in deeper soil layers. Th e type specimens of S. simplipodicus which are perhaps preserved in the Institute of Zoology, Chinese Academy of Sciences, or new topotypic material need to be examined to supplement the original description of Zhang which suff ers from the poor quality of its illustrations. Description of locality. For detailed descriptions of the cave and its exact locality see Burgers et al. (2005). Th e new species has been collected from the ceiling of the cave (H. Steiner, in lit.). Cave crickets, a spider, and the centipede Th ereuopoda longicornis co-occur with S. steineri (Steiner 2005, Jäger andPraxaysombath 2009).

Sinocallipus steineri
Origin of name. Named after the German biospeleologist Helmut Steiner, an active explorer of the caves of Laos, who collected the species.
Width of PT: 2-3<1=4<5<6<7<8<9<10. PT slightly higher than broad; ratio: 1.07 : 1. Dorsal side of collum and PT 2-3 smooth, ribbed only laterally; complete crests series appearing from PT 4 onwards. Midbody PT with 3+3 crests between ozopores; no secondary crest series, all crests fl attened, almost equally broad along the metazonal length, only slightly narrowed posteriorly and touching each other anteriorly. Ozopores on midbody PT lying between crests 3 and 4, visible from sixth to last but two PT. Paraprocts divided into smaller dorsal and bigger ventral sclerites. Each dorsal sclerite with a pair of macrosetae in a vertical line. Spinnerets: long and slender, ending with a long seta each. All setae on telson dark brown, contrasting with the whitish background.
Chaetotaxy: pleurotergal setae barely visible, minute, one each on PT 1 and 2, others presumably broken off .
Gonopods (Figs 22,23): similar to those of congeners, but process k is longer. Coxae (cx): process g laterally narrowed, not clavate as in the other congeners; apical part slighly truncated (in lateral view); k 2/3 the height of process g, slightly bent lateralwards at midlength; apex with a small hook pointing towards process g. Femoroid (fe): with three slender, acicular (n), and one shorter and subfalcate (m) terminal projections, latter almost half length of the longest projection. Cannula (ca): long and slender, not coiled, its distal part lying between processes h and z on trochanter of leg 9 in close proximity to the pore opening (p).
Female: unknown. Distribution. Only known from the type locality in Th ailand, Saraburi Province, Muang District, Sriwilai Cave Temple, 14°41'40"N, 100°54'34"E. Th e unique holotype was collected under a rock at the base of a limestone hill.

Discussion
Sinocallipus is remarkable in many aspects. In addition to its apparent primitiveness compared with other callipodidans, we here focus on the lack of noticeable gonopodal variation between species and the role of the 9 th male legs during copulation.

Gonopodal monotony vs. peripheral diversity
Th e genus Sinocallipus (as well as the monotypic family and suborder) can be defi ned by having each gonopod divided into a mesally expanded coxa bearing a cannula, and a telopodite (femoroid) without a prostatic groove bearing 2-4 acicular processes. Th e gonosternum lies at the base of the gonocoxae as in normal walking legs. In contrast to all other callipodidans which show considerable intrageneric variability in gonopod shape, gonopods in Sinocallipus are quite uniform. Th e diff erences mainly concern the shape and length of cannula, the length and shape of coxal processes g and k, and the number (2-4) of acicular projections of the femoroid. In contrast, peripheral characters such as the relative lengths of antennomeres (Fig. 25), the number of ocelli, the number of pleurotergites or even the shape of paraprocts and the coloration seems to provide more information for the distinction of the species. Th ere is a high degree of color variation in sinocallipods -from pale or light yellow-brownish in most of the species to dark brown in S. thai (the only known specimen of which was collected outside a cave). Body size also varies substantially, from around 40 mm in S. simplipodicus to more than 70 mm in S. deharvengi. Th e same is true for the length of antennae where S. deharvengi and S. jaegeri on one hand and S.   Zhang (1993).
thai on the other demonstrate the extreme cases (Table 2, Fig. 25). Th e shape of the trochanteral process of the 9 th male leg-pair also varies and could be used as a speciesspecifi c character .
Sinocallipus thus enters the ranks of millipede groups where the gonopods -often regarded as a sine qua non for species distinction in millipedes -are of little use for taxonomists while non-gonopodal ("peripheral", "somatic") structures provide characters for identifi cation. Hoff man (1981) called attention to what he called "diphasic evolution" in polydesmidan millipedes: the diff erence between related species lies either in the exterior morphology, with gonopods showing little diversity, or in the gonopod structure, with peripheral characters showing less variation, see also Hoffman (1990). Examples of millipede groups with monotonous gonopods and diverse peripheral characters include the oxydesmid genus Coromus (Hoff man 1990), parts of the julid genera Nepalmatoiulus, Dolichoiulus and Pachyiulus (Enghoff 1987, 1992, Frederiksen, Petersen andEnghoff , unpubl.), the rhinocricid genus Anadenobolus (Bond and Sierwald 2002) and the harpagophorid genus Th yropygus (Pimvichai, Enghoff and Panha, unpubl.). Shear et al. (2003) stated that the cannula must represent the functional element in Sinocallipus copulation. According to these authors the most plausible method of spermatophore or seminal fl uid transfer seems to be directly by the cannula which, being the longest gonopodal structure, could most easily contact the openings of the vasa deferentia to be "charged," and subsequently penetrate the female cyphopods during copulation. Shear et al. (2003) found further support for this notion in the structure of telopodite which lacks a prostatic groove. However, no explanation has been off ered for the function of the trochanteral lobe of 9 th leg-pair -a structure lacking analogues in other callipodidans.

Commentary on functional anatomy of gonopods and ninth male legs in Sinocallipus
A close-up photograph of the gonopodal region of S. steineri (Fig. 23) shows the distal part of the cannula embedded in the groove formed by the trochanteral processes on leg 9 in close proximity to the pore (p). Th is suggests that the 9 th legs play a role in the copulation process, provided that the interpretation of Shear et al.' is correct and indeed the cannula is the main structure used for sperm transfer. Besides mechanical support the trochanter probably provides secretions through the pore (p). However, until proven by direct observation, this statement remains speculative.

Other unusual morphological traits
Sinocallipus exhibits further traits which were previously unknown in Callipodida. Th e division of each paraproct into a smaller dorsal and a larger ventral sclerite seems in general to show no variation within the order. However, in S. deharvengi the paraprocts are divided exactly in the middle forming two nearly equal-sized halves (Fig. 9), while in all congeners they have the usual callipodidan shape. A character that might prove to be an autapomorphy for the genus is the presence of more than one seta (usually a pair, arranged in a vertical row) on the dorsal sclerite of each paraproct. Th is has been observed so far in four of the species and also in the female specimen of uncertain identity from the Snake cave, while it has not been recorded for the other species (where it might have been overlooked).

Distribution
Sinocallipus is the only genus in Callipodida entirely confi ned to the tropics, being hitherto known only south of the Tropic of Cancer, where its species are primarily confi ned to limestone caves and their surroundings. At present the genus range comprises the extreme South of China in Yunnan; Lang Son, Ha Noi, Quang Binh and Hai Phong provinces in North and Central Vietnam; Saraburi Province in South Central Th ailand; and Khammouan, Luang Phrabang and Champasak/Attapu prov- inces in Laos (Fig. 30). Shelley and Golovatch (2011) in their magnum opus on millipede biogeography presented updated maps of the distribution of the order Callipodida. Th ese authors regard Callipodida as exhibiting an exclusively Laurasian distribution pattern and the occurrence of callipodidans in China and SE Asia as resulting from "spread into these areas after accretion of the "proto-southeast Asia" Gondwana I terranes". Although their explicitly not phylogeny-based narrative is not entirely clear on this point, it seems that they regard the occurrence of callipodidans in China and SE Asia as secondary, resulting from dispersal from Laurasia. Th is explanation would imply a cladistically subordinate position of the Chinese and SE Asian callipodidans (see, e.g. Enghoff 1993) which, in the case of Sinocallipodidae, is in confl ict with the assumed basal position of this family. A phylogenetic analysis is obviously needed in order to better understand the evolution and biogeography of the order Callipodida.