Eutrichodesmus cambodiensis Srisonchai & Panha, 2020

Srisonchai, Ruttapon, Likhitrakarn, Natdanai, Sutcharit, Chirasak, Jeratthitikul, Ekgachai, Siriwut, Warut, Thrach, Phanara, Chhuoy, Samol, Ngor, Peng Bun & Panha, Somsak, 2020, A new micropolydesmoid millipede of the genus Eutrichodesmus Silvestri, 1910 from Cambodia, with a key to species in mainland Southeast Asia (Diplopoda, Polydesmida, Haplodesmidae), ZooKeys 996, pp. 59-91 : 59

Eutrichodesmus cambodiensis Srisonchai & Panha sp. nov. Figures 1 , 2 , 3 , 4 , 5W , 7T , 9 , 10

Material examined.

Holotype male (CUMZ-hpd0001), CAMBODIA, Kampot Province, Dang Tong District, near Wat Phnom Small, limestone hills, 10°42'12"N, 104°31'30"E, ca. 47 m AMSL, leg. C. Sutcharit, W. Siriwut, E. Jerutthitikul, P. Trach, S. Chuoy & R. Srisonchai (locatily no. C041), 16 September 2019. Paratypes. Twenty-three males, fifteen females (CUMZ-hpd0002), same data as holotype. Six males and six females (CUMZ-hpd0002) CAMBODIA, Kampot Province, Banteay Meas District, Prasat Phnom Totong, 10°41'49"N, 104°31'23"E, ca. 31 m AMSL, leg. C. Sutcharit, W. Siriwut, E. Jerutthitikul, P. Trach, S. Chuoy & R. Srisonchai (locatily no. C042), 16 September 2019. One male, one female (CIFI), same data as holotype. One male (ZRC_ENT00014160), one female (ZRC_ENT00014161), same data as holotype. Further specimens, non-types. Two broken males, two broken females, one male without gonopods, eight juveniles, two males and two females prepared for DNA extraction (CUMZ-hpd0002), same data as for holotype.

Etymology.

The specific epithet reflects the name of the country " Cambodia " where all specimens were collected and to which the new species appears to be endemic; adjective.

Diagnosis.

Body with incomplete volvation; metaterga with three transverse rows of regular and round tubercles, but no mid-dorsal projection (outgrowth) on metaterga; distofemoral process on gonopod telopodite very short, inconspicuous. Similar in all these characters to E. griseus Golovatch et al., 2009, but differs in having (1) live specimens and freshly preserved material pale greyish-brown or pale brown in colour; (2) the limbus crenulate, but not spinulate, crenulations being slightly longer than broad; (3) the acropodite curved and long, unciform, attenuated near tip; with a free solenomere starting from about midway; and (4) the solenomere digitiform, papillate, without hairpad.

Description.

Body length 5-7 mm (male) or 6-8 mm (female); width of mid-body metazonae ca. 0.9 mm (male) or ca. 1.2 mm (female). In width, head <collum <2 = 3 <4 <5-17, thereafter body gradually tapering towards telson. Females apparently longer and larger than males.

Colour (Fig. 1 ). Live specimens pallid greyish-brown or brown: head grey; antennae pale brown; collum, metaterga and paraterga greyish-brown; surface below paraterga, prozonae, sterna and legs brown. Specimens in alcohol after six months of presevration nearly the same in colour as in life.

Body (Fig. 2A ). General appearance as in Fig. 2A . Body long and slender. Adults with 20 rings. Volvation incomplete because of a slender body and short paraterga.

Head (Fig. 2B, C ). Slightly transverse, wider than high, densely pilose, not covered with collum from above. Vertex microvillose and microgranulate. A pair of small, poorly separated, paramedian knobs above antennal sockets. Isthmus between antennae ca. 1.3 times as wide as diameter of antennal socket. Epicranial suture deep and conspicuous. Labrum and genae sparsely setose.

Antennae (Fig. 2B, D ). Short and stout, clavate, densely setose, setae being long.

Antennomere 6 longest, with a group of bacilliform sensilla located inside a shallow distolateral pit near tip of each of antennomeres 5 and 6. Antennomere 8 with four sensory cones apically.

Collum (Figs 2A, C, E ; 3A ). Large, nearly semi-circular, a little broader than head, with regular and rounded tubercles arranged in five transverse rows: usually 7+7 tubercles in anterior (first) row, followed by 4+4, 1(0)+1(0), 3+3 and 4+4 tubercles in rows 2-5, respectively. Anterior margin truncate, slightly elevated, resembling that in E. griseus or some species of Pyrgodesmidae . Posterior margin round. Lateral margin narrow, directed laterad.

Tegument. Overall quite dull, some specimens encrusted with dirt. Head mostly microgranulate (labrum and clypeus smooth). Collum microvillose. Prozonae finely alveolate.

Suture between pro- and metazonae quite shallow and broad, more strongly alveolate and microgranulate than prozonae. Metaterga, paraterga, surface below paraterga, sterna, epiproct and hypoproct microgranulate and microvillose. Legs smooth.

Metaterga (Figs 2A, E-G ; 3A-C ). Metaterga2-19 each with three transverse rows of undiffentiated tubercles, pattern isostictic (arrangement regular in axial position). Anterior, intermediate and posterior rows each with 4+4 tubercles; those in second row on body rings 5-19 larger than in other rows. Each tubercle anteriorly with a short, spatulate, bisegmented seta. Mid-dorsal (axial) line missing.

Limbus (Fig. 3F ). Crenulate, each lobulation being slightly longer than broad, tip round.

Paraterga (Figs 2A, E-F ; 3A-C, E ; 5W ). Broad, slightly sloping down. Tip round and directed ventrolaterad. Paraterga 2 enlarged, in situ more strongly sloping down than on other rings, with four or five conspicuous lobules. Paraterga 3 and 4 shorter, narrower than others; each with four conspicuous lobules. Paraterga 5-18 mostly with four lobules, some rings with five ones.

Ozopores. Inconspicuous when seen in dorsal view. Pores small, oval in shape, lacking a porostele, opening laterally near rear margin of paraterga above it. Pore formula normal (5, 7, 9, 10, 12, 13, 15-19).

Pleurosternal ridges. Absent.

Epiproct (Fig. 3D, G, I ). Very short, flattened dorsoventrally; knob-like apically, with two pairs of inconspicuous setae (spinnerets), each spinneret located inside a tube-like structure, both dorsal and ventral spinnerets arranged inside a circular shallow depression.

Paraproct (Fig. 3G ). Normal, with two pairs of small setae.

Hypoproct (Fig. 3G, H ). Subtrapeziform, caudal margin truncate, with two small, inconspicuous, setiferous tubercles.

Spiracle. Simple, located above anterior and slightly before posterior legs.

Legs (Fig. 3J ). Quite short and stout, in situ almost reaching the tip of paraterga. Relative length of podomeres: tarsus> femur> (prefemur ≥ coxa) = postfemur = tibia> claw.

Sterna (Fig. 3D ). Narrow. Longitudinal depression between coxae in most body rings deep and narrow, only in ring 7 quite deep and wide for accommodating the shafts of gonopods. Transverse depression deep and wide.

Gonopod aperture. Very large, transversely ovoid, subequal to width of prozonite.

Gonopods (Figs 4 ; 7T ). Shafts when retracted reaching the anterior part of sternum 7 (base of legs 8). Coxa (cx) large and stout, subquadrate, microgranulate, with a few short setae distolaterally. Cannula (cn) simple, conspicuous, curved and slender, swollen at base, inserted into a small depression at base of telopodite on posteromedial side. Telopodite suberect; basal half (= prefemoral part) nearly straight; distal half curved. Distofemoral process (dp) very short, located at about midway of telopodite, triangular, dentate. Acropodite conspicuous, with neither a lobe nor a process, distally slightly attenuated and forming a hook-like tip, directed and curved mesad. Solenomere partially separated from acropodite, conspicuous, digitiform, papillate, originating at ca. 3/4 height of telopodite beyond distofemoral process; rather short, tip in situ directed anteriad, apically with a large papilla which is more conspicuous than other papillae. Seminal groove (sg) conspicuous, thick, running entirely on mesal surface of telopodite, terminating without hairpad by opening on the large papilla of solonomere.

Remarks.

Although the genital characters of females have not been used for taxonomic purposes in the present study, all females were examined. In all cases, the female non-genital characters were found similar to those found in males. The only difference which can be clearly seen using both live and preserved material is that females are apparently broader and longer than males (Fig. 1C ).

The general colouration does not show any variability and the paratypes do not differ significantly from the holotype. Across the type series of the new species, there was little intrapopulational variation in the number of tubercles on the collum and of lobes on the paraterga: an intermediate row (third or middle row) of the collum usually showed 1+1 tubercles, only sometimes 0+1 or 1+0 tubercles; paraterga of most specimens usually had four conspicuous lobes, only sometimes five. However, all these variations in most of the non-gonopodal characters were minor, neither significant nor consistent enough to be useful for taxonomic purposes, at least in the species under consideration. Little can be said about interpopulational variation in the new species because no variation has been noted between the two examined populations and no other specimens living at and around these two locations have been found.

Notably, E. cambodiensis sp. nov. shows a slightly elevated anterior margin of the collum (Figs 2A , 3A ). As this can easily be seen also in E. griseus , it is consistent with what Golovatch et al. (2009b) found. Currently, only these two Eutrichodesmus species have the collum elevated in the anterior part, this strongly resembling the typical condition in the micropolydesmoid family Pyrgodesmidae .

The new species has the same characters as found in a bunch of congeners and shares the combination: adults with 20 body rings; body with incomplete volvation; metaterga without mid-dorsal projections, with three transverse rows of tubercles; and gonopod telopodite with a distofemoral process. All above characters are present in E. basalis Golovatch et al., 2009; E. curticornis Golovatch et al., 2009; E. demangei Silvestri, 1910; E. filisetiger Golovatch et al., 2009; E. gremialis (Hoffman, 1982); E. griseus , E. multilobatus Golovatch et al., 2009; E. nadan Golovatch et al., 2016; E. parvus Liu & Wesener, 2017 and E. regularis Golovatch et al., 2009 (see also Key and Table 2 ). Even though some traits have been observed, shared, especially in the gonopodal telopodite, between-species differences are always marked. With respect to the most relevant feature which lies in certain details of gonopodal structure, E. cambodiensis sp. nov. seems to be morphologically more similar to E. griseus than to any other congener, in particular in having a very short distofemoral process and the solenomere partly separated from the acropodite by forming a conspicuous lobe.

Distribution and habitat.

It is worth noting that the new species was found only at the two sites. Surveys of other limestone and sandstone habitats surrounding the type locality (Kampong Trach) over a period of approximately two years have revealed no further specimens (Fig. 10 ). In showing a distribution of only two locations in a small and isolated limestone area, the new species can be suggested as being not only endemic to Cambodia, but also indigenous in Kampong Trach.

All specimens of the new species were hand-collected and found walking on humid rock walls of limestone caves (Fig. 9A ). The vast majority of millipedes were seen crawling on humid rocks, whereas only a minor part was found slowly walking on vegetation, shaded holes and rock crevices during the daytime (Fig. 9B, C, E ). It is important to note that specimens were commonly found under herb patches in a slightly shaded moist rock where the plant genus Epithema Blume, 1826 (family Gesneriaceae ) created a mass of roots and thin litter layer on the soil in the hole (Fig. 9C ). This is probably a particular microhabitat for E. cambodiensis sp. nov. Furthermore, we noted a co-occurrence between E. cambodiensis sp. nov. and the abundant Hypselostoma cambodjense Benthem Jutting, 1962, a microsnail (Fig. 9D ), within a portion of the moist rock walls, as well as in rock crevices, but without being sympatric with other millipedes in the same microhabitats.

The habitat preferred by the new species clearly appears to be limestone, especially near caves, although all specimens were found outside the caves, near the entrance zones. No material was collected at twilight, transition or deep zones inside the cave [for a characterisation of the zonal environment in caves, see Liu and Wynne (2019)]. Many of the small holes/caves at the type locality where E. cambodiensis occurs are highly humid and have diminished light, owing to the shade from large trees in the area.

A large concern would be the ongoing habitat destruction very close to the type locality, where a cement factory is located on the opposite side of the mountain. Many outcrops in the area appear to have been quarried and it seems plausible that the existence of the type locality would be threatened in the near future.

Observation of mating behaviour.

Interestingly, all specimens of the new species collected around moist organic material and plants near the caves were pairs of several mating couples (Figs 1C , 9E ). No single males or females were found separately. One presumption would be that individual millipedes were perhaps hidden in rock crevices during the daytime. The pairs of the new species mated during the rainy season when the rate of annual rainfall amount is quite high, which may imply the peak in mating occurring around September. The initial observations of the courtship were made by separating seven pairs into individual airflow plastic vials without human disturbance and we found that males appeared to initiate copulation by approaching the female from behind and then slightly reaching to the head region. The male took at least five hours grasping onto a female by its legs before it entwined and finally inserted its gonopod shaft into the female’s vulva.

Figures

Figure 1. Photographs of live Eutrichodesmus cambodiensis sp. nov., paratypes (CUMZ-hapld 00002) A pairs of mating couples B male and C mating couple. Not to scale.

Figure 2. Eutrichodesmus cambodiensis sp. nov., male paratype (CUMZ-hpd 0002) A whole body part B head and antenna C head and collum D antenna E anterior body part F body rings 9 - 13 (arrowhead points to ozopore) G posteriormost body rings and telson A lateral view B anterior view C, E-G dorsal view. Scale bars: 0.3 mm (B, C), 0.3 mm (E-G).

Figure 3. Eutrichodesmus cambodiensis sp. nov., male paratype (CUMZ-hpd 0002) A anterior body part B body rings 9 - 12 (arrowhead points to ozopore) C, D posteriormost body rings and telson, E mid-body ring F limbus of body ring 10 G last ring and telson H hypoproct I two pairs of apical setae (spinnerets) J leg 13 A-C, I lateral view D, G, H ventral view. Scale bars: 0.5 mm (A-E), 0.1 mm (H, I).

Figure 4. Eutrichodesmus cambodiensis sp. nov., right gonopod, male paratype (CUMZ-hpd 0002) A lateral view (dp = distofemoral process) B distofemoral process C mesal view (cx = coxa, cn = cannula, sg = seminal groove) D dorsal view E ventral view (arrowhead points to solenomere) F digitiform solenomere. Scale bars: 0.1 mm (A, C-E), 0.02 mm (B, F).

Figure 5. Body ring (posterior view) in several Eutrichodesmus species, number inside ring indicated rows of tubercles on metaterga. A-Q Species with mid-dorsal projections on metaterga. A E. anisodentus B E. aster C E. asteroides D E. astriproximus E E. astrisimilis F E. cavernicola G E. deporatus H E. dorsiangulatus I E. lipsae J E. macclurei K E. nodulosus L E. paraster M E. pectinatidentis N E. reclinatus O E. soesilae P E. steineri and Q E. subasteroides R-AA Species without mid-dorsal projections on metaterga R E. apicalis S E. arcicollaris T E. armatocaudatus U E. armatus V E. basalis W E. cambodiensis sp. nov. X E. communicans Y E. curticornis Z E. digitatus and AA E. distinctus. Not to scale. Figures modified from A, M Zhang (1995) B, C, Y, AA Golovatch et al. (2009 b) D, E, Q Golovatch et al. (2016) F Sinclair (1901) E, L, P Liu and Wesener (2017) H, S Zhang in Zhang and Wang (1993) I, R Golovatch et al. (2015) J, N Hoffman (1977) K Verhoeff (1939) O Makhan (2010) T, V, X, Golovatch et al. (2009 a) U Miyosi (1951) and Z Liu and Tian (2013).

Figure 7. Gonopod outline (mesal view of left and right gonopod) in several Eutrichodesmus species. A-N Gonopods of species with mid-dorsal projections on metaterga A E. anisodentus B E. aster C E. asteroides D E. astriproximus E E. astrisimilis F E. cavernicola G E. deporatus H E. dorsiangulatus I E. lipsae J E. macclurei K E. paraster L E. pectinatidentis M E. steineri and N E. subasteroides O-Z Gonopods of species without mid-dorsal projections on metaterga O E. apicalis P E. arcicollaris Q E. armatocaudatus R E. armatus S E. basalis T E. cambodiensis sp. nov. U E. communicans V E. curticornis W E. demangei X E. digitatus Y E. distinctus and Z E. elegans. Not to scale. Figures modified from A, L Zhang (1995) B, C, V, Y Golovatch et al. (2009 b) D, E, N Golovatch et al. (2016) F Sinclair (1901) G, K, M Liu and Wesener (2017) H, P Zhang in Zhang and Wang (1993) I, O Golovatch et al. (2015) J Hoffman (1977) Q, S, U Golovatch et al. (2009 a) R Miyosi (1951) W Silvestri (1910) X Liu and Tian (2013) and Z Miyosi (1951).

Figure 9. Habitat at the type locality of Eutrichodesmus cambodiensis sp. nov. A limestone outcrop B, C humid rock wall, sinkholes and crevices D co-occurrence of the new species with microsnail, Hypselostoma cambodjense Benthem Jutting, 1962 and E mating couple (male on top).

Figure 10. Known distribution of the Eutrichodesmus cambodiensis sp. nov. A limestone mount near Wat Phnom Small (type locality) B Prasat Phnom Totong.