Six new species of dragon millipedes, genus Desmoxytes Chamberlin, 1923, mostly from caves in China (Diplopoda, Polydesmida, Paradoxosomatidae)

Abstract Six new species of Desmoxytes are described from southern China: Desmoxytes laticollis sp. n., Desmoxytes simplipoda sp. n., and Desmoxytes similis sp. n., all three from caves in Guangdong Province; Desmoxytes phasmoides sp. n. also from a cave, and both epigean Desmoxytes spiniterga sp. n. and Desmoxytes variabilis sp. n., the latter trio from Guangxi Zhuang Autonomous Region. A modified key to all 20 Desmoxytes species currently known to occur in China is given.


Introduction
Millipedes in the genus Desmoxytes Chamberlin, 1923, belong to the tribe Orthomorphini, subfamily Paradoxosomatinae, family Paradoxosomatidae (Golovatch et al. 2012) and are often referred to as "dragon millipedes". This genus is conspicuous in its species generally showing a dragon-like appearance, with strongly wing-, spineor antler-shaped paraterga. Desmoxytes was first revised by Golovatch and Enghoff Germany (ZFMK), and the Zoological Museum, State University of Moscow, Russia (ZMUM).
Observations and dissections were performed using an Olympus SZ51 stereo microscope. The line drawings were prepared with the help of an Olympus SZX12 stereo microscope and a camera lucida attached to the scope. The photographs were taken with Canon EOS 40D and 7D cameras, further processed using Adobe Photoshop CS5 software.
Remark. Because of the pallid tegument and remarkably elongated antennae and legs, this species is most probably a troglobite. Paratypes. 1 ♂, 6 ♀ (SCAU), same locality and collecting data as the holotype. Name. To emphasize the legs being simple, devoid of modifications; adjective. Diagnosis. Using the latest key (Liu et al. 2014), this new species keys out to the superficially most similar D. longispina (Loksa, 1960), especially so due to spiniform paraterga and a condensed solenophore, but differs by the legs being devoid of modifications.

Desmoxytes similis
Name. To emphasize the particular similarities to D. simplipoda sp. n.; adjective. Diagnosis. This species seems to be especially similar to D. simplipoda sp. n., from Yangshan, Qingyuan, Guangdong, but differs by the setose process between ♂ coxae 4 showing a large pore and the lamella medialis of the gonopod solenophore a small lobule at about midlength.
Description. All characters as in D. simplipoda sp. n., except as follows.
Gonopods ( Fig. 7B-C) short. Coxite less than 1/3 the length of telopodite. Prefemur about half as long as acropodite. Femorite very short, slightly enlarged distad. Solenophore strongly condensed and divided into a large subtriangular lamella lateralis (ll) and a terminally evidently bifid lamella medialis (lm), the latter with a very small lobule (l) at about midlength.  Remarks. This species seems to be very similar to D. simplipoda sp. n., from Yangshan, Qingyuan, Guangdong. The only differences are outlined in the above diagnosis. Because of the nearly pallid tegument and extremely elongated antennae and legs, this species seems to be a troglobite. Paratypes. 1 ♂, 1 ♀ (SCAU), 1 ♂ (ZFMK), same locality and collecting data as the holotype.

Desmoxytes phasmoides
Name. To emphasize that superficially this new species somewhat resembles a stick insect, Phasmatodea; noun in apposition.  Diagnosis. Keys out to the superficially most similar D. minutubercula Zhang, 1986(Liu et al. 2014), especially so due to long spiniform paraterga and a particularly condensed solenophore, but differs by a pair of rounded, setose processes present between ♂ coxae 4 and the gonopod lamella medialis showing a distinct spine.
Description. All characters as in D. laticollis sp. n., except as follows.
Gonopods (Fig. 9D-F) subfalcate. Coxite very short, less than 1/3 as long as telopodite. Prefemur short, less than half as long as acropodite. Femorite rather long, curved ventrad. Solenophore highly condensed, divided into a small, rectangular lamella lateralis and a simple lamella medialis, the latter with a distinct spine (s) at about midlength; solenomere very short and flagelliform.
Remark. Because of the pallid tegument and extremely elongated antennae and legs, this species may well be a troglobite.  (Liu et al. 2014), judging from the ornamentation of metaterga, but differs by legs showing no modifications, in the metaterga supplied with more numerous setigerous spines, as well as the rather short femorite of the gonopod and the clearly coiled solenophore (cf. Kraus 2012).

Desmoxytes spiniterga
Description. All characters as in D. laticollis sp. n., except as follows.
Gonopods (Figs 10B, with coxite about 1/3 as long as telopodite. Prefemur almost half as long as acropodite. Femorite short and slender, slightly enlarged distad. Solenophore clearly coiled and divided into a large spiniform lamella lateralis and a very distinct and coiled lamella medialis. Solenomere relatively long.
Remark. Compared to cave-dwelling congeners, this species is much smaller and darker.   Diagnosis. This species seems to be especially similar to D. nodulosa Liu, Golovatch & Tian, 2014, from Cave II, Xiao'ao Xiang, Du'an Xian, Hechi, Guangxi, because both share very close patterns of metatergal ornamentation and particularly stout gonopods, but differs by the metaterga showing a variable pattern of setigerous spines, and the particularly complex gonopod solenophore.

Desmoxytes variabilis
Description. All characters as in D. laticollis sp. n., except as follows.
Gonopods (Fig. 14F-G) very short. Coxite less than 1/3 as long as telopodite. Prefemur less than half the length of acropodite. Femorite stout, apically with a distinct sulcus. Solenophore quite complex and compact, divided into two well differentiated lobes, a higher, bipartite and apically acuminate lamina medialis, plus a lower and curved lamina lateralis; solenomere short and flagelliform.
Remark. This obviously troglophilic species is rather eurytopic, occurring both outside and inside caves. It shows a remarkably variable pattern of spination on collum and metaterga (Figs 12-13), but the gonopod structure remains stable.

Conclusion
The family Paradoxosomatidae (Polydesmida) is among the largest in the entire class Diplopoda (nearly 200 genera and >950 species, amounting to about 60% of the total species diversity in the Oriental fauna), but it is highly uncharacteristic of caves.
Remarkably, Desmoxytes is the sole genus of Oriental paradoxosomatids that comprises numerous true cavernicoles (Golovatch 2015). Now that Desmoxytes encompasses 41 described species, of which half derive from mainland China, a few observations seem to be noteworthy. Species group delimitation lies beyond the scope of the present paper, as it focuses only on the Chinese fauna. It also seems somewhat premature given the rapidly growing number of species described lately and certainly many more still to be found across China and Southeast Asia. However, superficially all Desmoxytes spp. that are presumed troglobionts are highly troglomorphic and have only been encountered in the karsts of southern China. Only among such congeners there are several that show remarkably long and spiniform paraterga, obviously an apomorphic troglomorphism.
The diversity of Desmoxytes as currently known may seem biased to cave-dwellers, in part because much of the collecting and taxonomic exploration efforts still focus on cavernicoles alone. Interestingly, however, in contrast to China, not a single troglomorphic species of Desmoxytes has been encountered in the numerous well-explored karsts of Thailand, Laos or Vietnam, even though epigean Desmoxytes are likewise very common and diverse in Indochina.