Xystodesmus parvus, Korsós & Nakamura, 2025

Korsós, Zoltán & Nakamura, Yasuyuki, 2025, Review of the millipede genus Xystodesmus (Diplopoda, Polydesmida), with seven new species from the southwestern part of Japan, ZooKeys 1231, pp. 191-232 : 191-232

Xystodesmus parvus sp. nov.

Figs 6 A – E , 16 D

Type material.

Holotype: • male, Japan, Central Ryukyus, Kagoshima Pref., Amami Group, Okinoerabu-jima Isl., Oyama botanical garden , 27°21'56.4"N, 128°34'00.0"E, 240 m a. s. l., 13 June 2010, leg. Z. Korsós and Y. Nakamura ( NSMT -My 542 ) . Paratypes: • 4 females ( NSMT -My 543 ), 1 male ( RUMF -ZD-00941 ), 3 females ( RUMF -ZD-00942 ), same locality and date as holotype .

Diagnosis.

Differs from its congeners by the small body size (length under 23 mm), and by the male gonopods lacking coxal apophysis and having two simple branches (prefemoral process and acropodite) subequal in length and bent parallel together. The closest species is the similarly small X. sesokoensis sp. nov., but its prefemoral process has two small branches at tip, and its acropodite is longer, the end is thicker with a small tooth.

Description.

Length 19–22 mm, midbody width with paraterga 4.1–4.2 mm, midbody metatergal length 0.9–1.1 mm, collum width 3.1–3.2 mm, median collum length 1.3–1.4 mm. Body sides between segments 5–15 subparallel.

Head smooth, with two frontal setae, epicranial suture distinct. Antennal articles slightly clavate, first article sub-globose, articles 2–6 subequal in length, article 7 small, as long as wide.

Collum in dorsal view oval, edges rounded, with well-developed anterior ridge, laterally even stronger like paranotum, corners rounded. Pro- and metaterga completely smooth, transverse depression in metaterga short but noticeable. Anterio-lateral edge of paranota rounded, posterio-lateral corner of segments 2 and 3 rounded, lacking projection; on 4 with small projection, from 5 increasingly pointed, triangular, sublateral excavations on posterior margin becoming stronger. Lateral sides of paranota straight, outline of segments clearly delimited. Pore formula normal, pores in lateral central position on narrow paranota.

Segments 16–19 gradually tapering, posterior corners becoming obtuse, sublateral excavations disappearing. Epiproct in dorsal view triangular, in lateral view slightly curved ventrad, with 4 + 4 large setae on tubercles on lateral sides, projection with 2 + 2 apical setae; paraprocts smooth, with two pairs of setae, upper ones on margin, lower ones on side; hypoproct semicircular with two setae on small tubercles.

Bases of midbody leg pairs well separated (by 1.2 mm in male, 1.6–1.8 mm in females), sterna smooth and wide, pro- and metasterna fused. Coxa short, rectangular; prefemur ~ 2 × as long as wide, with well-developed ventral spine; femur 1.5 × longer than prefemur, incrassate; postfemur small, sub-globose, tibia slender, approximately same length as postfemur, tarsus 2 × as long as tibia, slender, tapering towards small, curved claw.

Colour of living specimens (Fig. 16 D ) pale brown, collum, segments 2, 18, 19, and epiproct darker, all metaterga with dark posterior margin. Underside of head, antennae, legs, and whole ventral side pale white. Sides of collum and all paranota (except segment 19) with faint, pinkish-orangish spots.

Male sexual characters. Second leg pair with small coxal processes provided with three or four strong setae (Fig. 6 D ), sterna of segments 4–6 and further legs without any modifications. Gonopods (Fig. 6 A – C ): Coxa stout, ~ 1.2 × longer than wide, coxal apophysis completely lacking, apophyseal macroseta (ms) relatively small. Prefemur short, stout, parallel-sided, densely setose on ventral side, with a few setae on dorsal side; prefemoral process (pfp) slender, shorter than acropodite, bent ventrad and ending in a long, pointed tip; acropodite (a) slightly broader and longer, bending subparallel to prefemoral process, gradually tapering towards somewhat broader, leaf-like tip (t) (Fig. 6 B ). Prostatic groove runs along mesal side of acropodite.

Female sexual characters. Cyphopods (Fig. 6 E ) situated in deep, joint aperture behind leg pair 2, loosely encapsulated in vulval sacs, well separated from each other. Receptacula (not shown in figure) on both anterior and posterior side, setose only along margins, with pointed mesal tips; operculum (op) elongated with three strong setae; bursal valves (v) hidden between high receptacula, with short setae only.

Remarks.

The new species was found in a protected botanical garden on the top of the central hill on the 93 km 2 Okinoerabu-jima Island. The vegetation cover is subtropical broad-leaved evergreen forest, and the specimens were collected in the deep, humid, top-soil litter layer. No sympatric species of millipede were found.

Etymology.

Named after its small size (parvus, in Latin). Adjective, masculine.

Figures

Figure 6. Xystodesmus parvus sp. nov., paratypes from Okinoerabu-jima Island, Kagoshima Pref. A – C right gonopod of male paratype, lateral, mesal, and ventral (B, telopodite only) views, respectively D 2 nd leg pair (from femur omitted) of male paratype, anterior view E left cyphopod of female paratype (receptaculum omitted), anterior view. Abbreviations: a = acropodite, ms = macroseta, op = operculum, pfp = prefemoral process, t = tip of acropodite, v = valve. Scale bars: 0.5 mm.

Figure 16. Live habitus of new Xystodesmus millipede species A X. fasciatus sp. nov., male paratype, Fukiage, Kagoshima Pref. B X. keramae sp. nov., male paratype, Aka-jima Isl., Okinawa Pref. C X. kumeensis sp. nov., male paratype, Kume-jima Isl., Okinawa Pref. D X. parvus sp. nov., male paratype, Okinoerabu-jima Isl., Kagoshima Pref. E X. rebekae sp. nov., male paratype, Mt. Yae-dake, Okinawa-jima Isl., Okinawa Pref. F X. sesokoensis sp. nov., male holotype, Sesoko-jima Isl., Okinawa Pref. G unidentified female, Tokashiki-jima Isl., Okinawa Pref. H unidentified female, Tokuno-shima Isl., Kagoshima Pref. Not to scale.