A revision of dragon millipedes II: the new genus Nagaxytes gen. nov., with the description of three new species (Diplopoda, Polydesmida, Paradoxosomatidae)

. The ‘ acantherpestes ’ group of dragon millipedes, formerly placed in the genus Desmoxytes Chamberlin, 1923, is revised and assigned to the new genus Nagaxytes Srisonchai, Enghoff & Panha gen. nov. Desmoxytes acantherpestes Golovatch & Enghoff, 1994 is the type species of the new genus and is redescribed as N. acantherpestes (Golovatch & Enghoff, 1994) gen. et comb. nov. Three new species are described from Thailand: N. erecta Srisonchai, Enghoff & Panha gen. et sp. nov. and N. gracilis Srisonchai, Enghoff & Panha gen. et sp. nov. from Kanchanaburi Province, and N. spatula Srisonchai, Enghoff & Panha gen. et sp. nov. from Tak Province. All new species are endemic to western Thailand and all are restricted to limestone habitats. Complete illustrations of external morphological characters, an identification key, and a distribution map are provided.


Introduction
subdivided the dragon millipede genus Desmoxytes Chamberlin, 1923, sensu Golovatch & Enghoff (1994) into five groups based on morphological characters and DNA sequence data; they regarded each of the groups as a separate genus.In the present article, the second in a series of articles about a revision of the dragon millipedes, we revise the 'acantherpestes' group sensu Srisonchai et al. (2018).For this group we erect the new genus Nagaxytes Srisonchai, Enghoff & Panha gen.nov. to include Desmoxytes acantherpestes Golovatch & Enghoff, 1994 from western Thailand as well as three new species.
The new genus Nagaxytes gen.nov. is narrowly distributed and restricted to limestone areas.All species are known only from western Thailand: Kanchanaburi, Prachuap Khiri Khan and Tak Provinces.= above sea level ca.

CUMZ
= about, around (circa) Gonopod terms for the genus Nagaxytes gen.nov., and their abbreviations Acropodite = apical part of gonopod; including femorite, solenophore and solenomere ca = cannula, a short tube, lever-like, curved, slender; originating from coxa, tip inserted into concavity in the prefemoral part cx = coxa, basal part of gonopod, rather stout, connecting to seventh body ring, attached to apertural rim dorsally; with a distoanterior group of setae fe = femur, longest part of gonopod, straight; accommodates seminal groove ll = lamina lateralis, a distinct lobe on distal part of gonopod; sometimes short, stout, compact; sometimes long; rarely with a spatulate lobe lm = lamina medialis, a large part distally on gonopod, very long, snake-like ls = lateral sulcus, a distinct sulcus distally on femur, conspicuously deep or shallow, visible in lateral view ms = mesal sulcus, a distinct sulcus distally on femur, conspicuous and deep, usually seen in mesal view op = ozopore pfe = prefemoral part (= prefemur), basal portion of telopodite, densely setose pof = postfemoral part (= postfemur), a short part of telopodite, supporting solenophore and solenomere, demarcated from femur by lateral sulcus and mesal sulcus sg = seminal groove, a conspicuous groove, similar to a tunnel, seen as a transparent line, visible on femur in mesal view sl = solenomere, a usually long, flagellum-like appendage, originating on base of solenophore sph = solenophore (= tibiotarsus), apical part of telopodite, consisting of lamina lateralis and lamina medialis Telopodite = Main part of gonopod, pivoting on coxa; including prefemoral part, femorite, solenophore and solenomere

Positional/directional terms in gonopod description
Traditionally the gonopods are depicted as rotated 90° up from their in situ position (following the terminology of Srisonchai et al. 2018).Dorsal = position on the side nearest to the body ring Ventral = position on the side farthest away from the body ring Mesal = position on the side nearest to the midline Lateral = position on the side furthest from the midline Dorsad = direction towards the body ring Ventrad = direction away from the body ring Mesad = direction towards the midline Laterad = direction away from the midline We use 'sub-' as a prefix referring to positions and directions slightly different from the ones given above.For example, 'subdorsal' means a position close to, but not quite on the dorsal side.

Etymology
'Naga' is a Sanskrit and Pali word, relating to a category of snake-like spirits in Buddhist and Hindu mythology, and refers to the snake-like shape of the lamina medialis of the gonopod; '-xytes' ensures harmony with Desmoxytes (and its synonym Pteroxytes Jeekel, 1980).

General description of Nagaxytes gen. nov.
The description applies to adult males and females, except for the gonopods or when 'male' is specified (Figs 1-3).The general description of gonopods is based mainly on Nagaxytes gracilis gen.et sp.nov. .
Colour (Figs 1,(11)(12)17,22).Specimens in life with brown or reddish brown colour or pinkish brown (possibly aposematic colouration).Colour in alcohol: all specimens partly faded to pale whitish brown after one year's preservation in alcohol; specimens kept in darkness faded more slowly.
PleuroSternAl CArinAe (Fig. 3B).Forming a complete crest on ring 2, smalls ridges on ring 3 and/or 4, missing on remaining body rings.
gonoPodS .Coxa longer than prefemoral part, with a distoanterior group of setae.Cannula long or short.Telopodite straight.Prefemoral part usually shorter than femur, sometimes subequal in length to femur.Femur usually long, sometimes quite short.Seminal groove running entirely on mesal surface of femur.Mesal sulcus and lateral sulcus conspicuous.Postfemoral part conspicuous, shorter than femur.Solenophore well-developed: lamina lateralis variously modified; swollen, sometimes long digitiform/lamella-like and projecting, sometimes with spatula-like lobe: lamina medialis longer than lamina lateralis, snake-like, tip curving down.Solenomere relatively long.

Distribution and habitat
This genus is known only from the western part of Thailand: Prachuap Khiri Khan Province (Hua Hin and Kui Buri Districts), Kanchanaburi Province (Sai Yok and Thong Pha Phum Districts) and Tak Province (Mae Sot and Umphang Districts) (Fig. 27).All four species seem to be local endemics, highly restricted to limestone habitats, and all have narrow distribution ranges.The specimens were usually found on humid rocks, rock walls, leaf litter or surface roots of trees.Some species can be found syntopically in the same habitat with other dragon millipede species.

Distribution and habitat
This species is known from two locations (Hua Hin and Ban Yan Sue) in Prachuap Khirikhan Province.We believe that the holotype was probably collected from limestone habitats because the type locality (near Hua Hin) lies in a limestone area.Specimens collected by us were from limestone habitats.It has been found crawling on rocks or on leaf litter.This species is likely to be syntopic with Desmoxytes planata (Pocock, 1895) at Ban Yan Sue; however, we noticed that the habitats of these two species are clearly different.Nagaxytes acantherpestes gen.et comb.nov.lives on the ground or on limestone rocks while D. planata was found on tree trunks near garbage.Decker (2010) identified one male in NHMG, collected from Thanboke Khorani National Park, Krabi Province (8°23′12″ N, 98°44′16″ E) as D. acantherpestes.This specimen might perhaps be 'D.' gigas Golovatch & Enghoff, 1994 (in the 'gigas' group) because the location falls in the distribution range for this group in South Thailand whereas Nagaxytes gen.nov.(the 'acantherpestes' group) is limited to western Thailand.Moreover, Thanboke Khorani National Park and Hua Hin are far apart, about 500 km.This species is distributed in a narrow area; we regard N. acantherpestes gen.et comb.nov.as endemic to Prachuap Khiri Khan Province, Thailand.

Remarks
In the original description, Golovatch & Enghoff (1994) did not comment on the live colouration of this species.We did not photograph living specimens, but our collector noticed a brown colouration.Golovatch & Enghoff (1994) also described D. acantherpestes as lacking pleurosternal carinae, but after we re-examined the holotype and examined all newly collected specimens, we found the pleurosternal carinae as crest-like on ring 2, as small ridges on ring 3, thereafter absent.There is a variation in the tip of the epiproct which in some specimens is subtruncate, in others slightly emarginate.

Etymology
The name is a Latin adjective and refers to the erect lamina lateralis of the gonopod telopodite.

Distribution and habitat
Nagaxytes erecta gen.et sp.nov. is known only from Kanchanaburi Province, Thailand.All specimens were collected from limestone habitats during the rainy season (July-October).Lots of specimens were usually found near human areas, where some habitats were being destroyed for construction of a temple or bureau of monks.
At Daowadueng Cave, the new species lives syntopically with N. gracilis gen.et sp.nov.and Desmoxytes purpurosea Enghoff, Sutcharit & Panha, 2007, in the same habitat.Desmoxytes planata was also found near the habitat of the new species at Phuphrai Thannam Resort and Wat Tha Kha-nun.We assume that D. planata occurs in a different microhabitat because the areas where we collected it are very strongly influenced by humans, and all specimens were seen crawling on statues and concrete.
We have only found N. erecta gen.et sp.nov. in a narrow area (100 km 2 ) along the huge limestone mountain range in Sai Yok and Thong Pha Phum Districts.Therefore, we regard this species as endemic for the Thai fauna.

Remarks
There is a considerable variation in the live colouration; two colour morphs can be distinguishedbrownish red and brown.All specimens from Ban Nong Bang (near Wat Pha Sukit Suwannaket) show a brownish red colour whereas specimens from the remaining localities exhibit a brown colour (except at Daowadueng Cave: both reddish brown and brown colour morphs occur in the same place, even the same habitat).A further morphological difference between these two colour morphs concerns the size of cones/spines (anterior row) on metaterga 16-19: conspicuous in the reddish brown colour morph, inconspicuous in the brown morph.However, the gonopod characters are virtually identical.A similar phenomenon is also found in Desmoxytes cervina in which two colour morphs share identical gonopod characters (Srisonchai et al. 2018).Therefore, we regard the differences in colour as interpopulational variation.An intrapopulational variation was also found in the: -tip of epiproct: in some specimens subtruncate, in others slightly emarginate.

Diagnosis
Metaterga 4-19 with one row of 2+2 posterior spines (anterior row absent).Similar in this respect to N. acantherpestes gen.et comb.nov., but differs from this species by having paraterga longer; degree of elevation of paraterga higher; sternal lobe between male coxae 4 incompletely bilobed; lamina lateralis long, lamella-like, thin, slender, tip round and directed ventrad.

Etymology
The name is a Latin adjective, referring to the slender lamina lateralis of the gonopod telopodite.
PleuroSternAl CArinAe.On body ring 2 long, crest-like; on body rings 3 and 4 small ridges; thereafter missing.

Distribution and habitat
Nagaxytes gracilis gen.et sp.nov. is known only from Sai Yok District, Kanchanaburi Province.All specimens were collected on humid rocks, superficial tree roots and litter in limestone habitats.It lives in the same habitat with D. purpurosea, D. golovatchi Srisonchai, Enghoff & Panha, 2018 and N. erecta gen. et sp. nov. (q.v.).The new species occurs in a narrow distribution area along the huge limestone range which is entirely contained within Sai Yok District.We thus consider this species to be endemic to Kanchanaburi Province, Thailand.

Remarks
The vivid pink paraterga are probably aposematic.Nagaxytes gracilis gen.et sp.nov.was noticeable in the field by the contrast of its bright pink colour to brown rocks.
There is a variability in the tip of the epiproct: in some specimens subtruncate, in others slightly emarginate.Srisonchai, Enghoff & Panha gen. et sp. nov. urn:lsid:zoobank.org

Etymology
The name is a Latin noun in apposition, referring to the spatulate lobe on the lamina lateralis.

Distribution and habitat
Known only from Tak Province.Almost all specimens were seen crawling on rocks, some on leaf litter in limestone habitats.Some juveniles were collected from the leaf litter (probably in moulting chambers).In the field, the specimens blended perfectly with brown rocks and leaf litter.The type locality for this species is situated beside road no. 12 (Tak-Mae Sot) near Khun Phawo National Park.We noticed that the forest beside the road is being destroyed for road construction, some parts of the limestone forest are being cut down.
For the time being, only five recorded locations are reported in the quite narrow distribution range of this species.After several intensive surveys we consider N. spatula gen.et sp.nov. to be endemic to Tak Province, Thailand.

Remarks
We divide this species into two main populations, each restricted to a separate limestone areas: -North populations: Chao Por Phawo Shrine, Wat Tham Inthanin and Wat Pho Thi Khun (Wat Huai Toey).-South populations: Tham Takhobi (Takhobi Cave) and Doi Hua Mod.Specimens of the North populations (24-26 mm in male, 26-28 mm in female) seem to be longer than those of the South populations (22-24 mm in male, 24-25 mm in female).However, other morphological characteristics, especially gonopod characters, are identical.

Discussion
On the basis of our morphological study and a preliminary DNA sequence analysis (work in progress), the 'acantherpestes' group as defined by Srisonchai et al. (2018) is here described as a new genus which includes 'Desmoxytes' acantherpestes and three new species.The new genus Nagaxytes gen.nov. is well-characterised by having subspiniform paraterga, unmodified male femora, as well as a curved and long lamina medialis.Each of the four species can be easily distinguished from its congeners by distinctive gonopod characters, especially the shape of the lamina lateralis in combination with other morphological characters.
Nagaxytes erecta gen.et sp.nov.includes two colour morphs: brownish red and brown.Moreover, the size of tubercles/cones/spines (anterior row) on metaterga 16-19 also differs between the two colour morphs: anterior row of tubercles/cones/spines conspicuous in the brownish red morph, inconspicuous in the brown morph.However, other morphological characters are clearly identical, especially gonopod characters: lamina lateralis long, thick, digitiform (Figs 14,17).Interestingly, the two morphs mainly occur allopatrically, although at Daowadueng Cave and Wat Sunantha Wanaram, they were found syntopically in the same habitat.This case is similar to that of Desmoxytes cervina: similarity in several morphological characters, but differences in colour between two allopatric and/or sympatric populations (Srisonchai et al. 2018).We hope that our molecular phylogeny work combined with morphological studies will shed more light on relationships within populations, within species, within the genus Nagaxytes gen.nov., as well as among its closely related genera.
Nagaxytes erecta gen.et sp.nov.has been found in partial sympatry with N. gracilis gen.et sp.nov. at Daowadueng Cave and Wat Sunantha Wanaram in Kanchanaburi Province.Both species show a similar pattern of gonopod shape and share a long lamina lateralis (e.g., Figs 15D, 21D), yet they are not identical.The differences in shape of the sternal lobe between male coxae 4 and the pattern of row of spines on metaterga support regarding them as different taxa.Although N. erecta gen.et sp.nov.and N. gracilis gen.et sp.nov.have been found to be syntopic, even collected from the same habitat, the details of their microhabitats have not yet been observed and they may not co-occur in a strict sense.
= Chulalongkorn University Museum of Zoology, Bangkok, Thailand MHNG = Natural History Museum, Geneva, Switzerland NHMUK = Natural History Museum, London, UK NHMW = Natural History Museum, Vienna, Austria ZMUC = Natural History Museum of Denmark (Zoological Museum), University of Copenhagen, Denmark ZMUM = Zoological Museum, University of Moscow, Russia Other abbreviations used in the text ASRU = Animal Systematics Research Unit, Department of Biology, Faculty of Science, Chulalongkorn University, Bangkok, Thailand a.s.l.
two rows of spines (1+1 or 2+2 spines in anterior row, 2+2 spines in posterior row).Similar in this respect to N. erecta gen.et sp.nov., but differs by having: degree of elevation of paraterga higher; apical tubercles of epiproct inconspicuous; surface near lateral sulcus swollen as long ridge; lamina lateralis broad, with a long and conspicuous spatula-like lobe; lamina medialis very long, curved, apically hook-like; tip of solenomere terminating in two curved processes.