Spinaxytes Srisonchai, Enghoff & Panha

Srisonchai, Ruttapon, Enghoff, Henrik, Likhitrakarn, Natdanai & Panha, Somsak, 2018, A revision of dragon millipedes IV: the new genus Spinaxytes, with the description of nine new species (Diplopoda, Polydesmida, Paradoxosomatidae), ZooKeys 797, pp. 19-69 : 19

Spinaxytes Srisonchai, Enghoff & Panha gen. n.

Type species.

Spinaxytes krabiensis Srisonchai, Enghoff & Panha, gen. et sp. n.

Diagnosis.

The genus Spinaxytes gen. n. is characterized by:

1. Paraterga spiniform.

2. Metaterga with two rows of tubercles/cones/spines.

3. Postfemoral part of gonopod conspicuous, demarcated from femur by deep mesal and lateral sulci.

4. Lamina lateralis distinctly demarcated from lamina medialis.

5. Lamina medialis very long, curved, larger and longer than lamina lateralis.

Etymology.

The name is a noun in apposition; from the Latin ‘spina’, referring to the spine-like paraterga of all constituent species; ‘–xytes’ ensures harmony with Desmoxytes (and its synonym ' Pteroxytes ').

Included species.

1. Spinaxytes biloba Srisonchai, Enghoff & Panha, sp. n.

2. Spinaxytes efefi Srisonchai, Enghoff & Panha, sp. n.

3. Spinaxytes hasta Srisonchai, Enghoff & Panha, sp. n.

4. Spinaxytes krabiensis Srisonchai, Enghoff & Panha, sp. n.

5. Spinaxytes macaca Srisonchai, Enghoff & Panha, sp. n.

6. Spinaxytes palmata Srisonchai, Enghoff & Panha, sp. n.

7. Spinaxytes sutchariti Srisonchai, Enghoff & Panha, sp. n.

8. Spinaxytes tortioverpa Srisonchai, Enghoff & Panha, sp. n.

9. Spinaxytes uncus Srisonchai, Enghoff & Panha, sp. n.

Remarks.

The new genus is easily distinguished from other genera of dragon millipedes by having spiniform paraterga, lamina lateralis smaller and shorter than lamina medialis, lamina medialis long and curved. Some species of the genus Hylomus Cook & Loomis, 1924, share spine-like paraterga; however, the gonopod details are totally different.

General description of the genus Spinaxytes . The description applies to adult males and females, except for the gonopods and when “male” is specified (Figs 1, 2, 4). The general description of the gonopods is based mainly on Spinaxytes krabiensis gen. et sp. n. (Figs 3, 5).

Size. Body length ca. 18-33 mm (male) ca. 16-33 mm (female), width 1.0-2.2 mm (male) 1.3-2.9 mm (female), size varies between species, usually female a bit longer than male.

Colour. Most species in life with dark brown colour. Colour in alcohol: all specimens partly faded to pale brown after 5 years’ preservation in alcohol; specimens kept in darkness faded more slowly.

Antennae (Figure 1 A–C). Extremely long and slender, covered by delicate setation, usually reaching backwards to body rings 7-10 (male) and 6-8 (female) when stretched dorsally. Antennomere 3 = 4> 5 ≥ 2> 6> 1> 7> 8.

Head. Delicately setose; vertex, labrum and genae sparsely setose; epicranial suture conspicuous as a deep, brown or black stripe.

Collum (Figure 2A, C). With three regular transverse rows of setiferous tubercles/cones; number of tubercles/cones in each row varies between species. Paraterga wing-like/spiniform, usually elevated at ca. 10°-30°, directed laterad/caudolaterad/caudad, with one or two conspicuous/inconspicuous notches at lateral margin.

Tegument. Quite dull, sometimes shining; collum, metaterga and surface below paraterga smooth/microgranulate; prozona finely shagreened; paraterga, epiproct and sterna smooth. Stricture between prozona and metazona shallow, wide.

Metaterga (Figure 2A, D, G). With two regular transverse rows of setiferous cones/tubercles (in anterior row) and cones/spines (in posterior row); number of tubercles/cones/spines in each row varies between species. Transverse sulcus on metaterga shallow and wide in body rings 5-18. Mid-dorsal (axial) line missing.

Pleurosternal carinae (Figure 2B). Forming a complete, tooth-like crest on ring 2, a short ridge on ring 3, missing on remaining body rings.

Paraterga (Figs 1A, B, D; 2A, B, D, E, G, H). Spiniform, long (except S. biloba sp. n.: quite short), extremely elevated at ca. 45°-80° (male) 40°-70° (female). Callus and shoulder poorly developed, inconspicuous. Anterior margin with two distinct denticles; on body rings 9, 10, 12, 13, 15-19 without a third denticle at lateral margin near tip. Degree of elevation of paraterga in male usually higher than in female. Posterior angle straight. Tip pointed and sharp. Ozopore visible from dorsal/dorsolateral/lateral view, round, small.

Telson (Figure 2F, G, L, N). Epiproct usually long, apically with two pairs of conspicuous setae (spinnerets) arranged at the corners of a square, not in a depression, anterior pair close to apical tubercles. Paraprocts convex. Hypoproct usually subtrapeziform, sometimes subsemicircular/subtriangular; caudal margin often round, sometimes subtruncate/angular, with two conspicuous/ inconspicuous setiferous tubercles.

Sterna (Figs 1E, 2K). Sparsely setose, cross-impressions shallow in all species. Sternal lobe between male coxae 4 varies in shape; subtrapeziform/long subrectangular/bifurcate/spear-like; one or two pores seen in posterior view.

Legs (Figs 1F, 2M). Extremely long and slender. Relative length of podomeres: femur ≥ tibia> tarsus ≥ postfemur> prefemur> coxa> claw. Male femora mostly without modification, sometimes male femora 6, 7 or 7 or 8, 9 with hump/apophysis ventrally in distal part.

Gonopods (Figure 3). Coxa shorter than femur, sometimes subequal in length to femur. Cannula long and slender. Telopodite erect. Prefemoral part usually almost half as long, sometimes ca. 2/3 as long as femur. Acropodite erect. Femur long and straight. Seminal groove running entirely on mesal surface of femur. Mesal sulcus and lateral sulcus conspicuous, deep. Postfemoral part conspicuous, usually small and narrow, sometimes broad and wide, rarely very large. Solenophore variously modified in shape between species: lamina lateralis obviously demarcated from lamina medialis, smaller and shorter than lamina medialis; lamina medialis long, base stout, slightly attenuated near the curved tip. Solenomere long, slender, curved, supported by solenophore.

Distribution and habitat.

All species of the new genus are allopatric. However, some of the new species can be found in syntopy with some species of Desmoxytes . The nine species described here are confined to limestone habitats and have narrow distributions; we therefore regard them as endemic. All species blend perfectly with habitat environment, mostly living on humid rock walls and/or inside small caves.

According to the current knowledge, Spinaxytes gen. n. is distributed only in the Malay Peninsula (south Myanmar, south Thailand, and north Malaysia): Myanmar: Thanintharyi Region; Thailand: Chumphon Province (Thung Tako, Mueng Chumphon, Lang Suan and Sawi Districts), Surat Thani Province (Phanom District), Phang Nga Province (Mueng Phang Nga and Takua Thung Districts), Krabi Province (Ao Luek and Muaeng Krabi Districts); Malaysia: Perak State (Figure 30).