Xystodesmus sesokoensis, Korsós & Nakamura, 2025

Xystodesmus sesokoensis sp. nov.

Figs 8 A – C View Figure 8 , 16 F View Figure 16

Type material.

Holotype: • male, Japan, Central Ryukyus, Okinawa Pref., Okinawa Group, Sesoko-jima Isl., Ominebaru , 26°38'36.7"N, 127°52'4.7"E, 11 March 2012, leg. Z. Korsós and K. Watanabe ( NSMT -My 546 ) GoogleMaps . Paratypes: • 1 male and 1 juvenile, same locality and date as holotype ( HNHM diplo-04546 ) GoogleMaps .

Diagnosis.

A small-sized Xystodesmus , with typical colour pattern, pale brown with orange paranotal spots. In its adult size, the most similar species is X. parvus sp. nov. that has two simple branches whereas X. sesokoensis sp. nov. has a prefemoral process with two small branches at tip, and a long, bending acropodite with a thickened end and a small tooth. Gonopods are somewhat similar to those of X. fasciatus sp. nov. but are larger, with a strong coxal apophysis, and its prefemoral process is much wider.

Description.

Total body length 19–20 mm, midbody paratergal width 3.7 mm, length 0.8 mm, collum width 2.9–3.0 mm, length 1.3 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 small anterior ridge, corners rounded. Pro- and metaterga completely smooth, transverse depression not visible. Segments 2 and 3 rectangular, both anterio- and posterio-lateral edge of paranota rounded, lacking projection; small projection starts on segment 4, then 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 disappear. Epiproct in dorsal view triangular, blunt, 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 weakly separated, 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 F View Figure 16 ) uniformly yellowish brown, only epiproct darker. Head, antennae, legs, and whole ventral side pale yellowish-greyish. Sides of collum and all paranota (except segment 19) with strong, pinkish-orangish spots.

Male characters. Second leg pair with small coxal processes provided with three or four strong setae (as in X. parvus sp. nov., Fig. 6 D View Figure 6 ), sterna and coxae of further legs without any modifications. Gonopods (Fig. 8 A – C View Figure 8 ): Coxa stout, sub-globose, approximately as long as wide, instead of coxal apophysis only a small bump, with strong apophyseal macroseta (ms) above. Prefemur short, rectangular, densely setose on ventral side, with a few setae on dorsal side; prefemoral process (pfp) slender, shorter than acropodite, bent ventrad and ending in two small projections; acropodite (a) slightly broader, longer, only slightly bending subparallel to prefemoral process, gradually thickening towards tip, ending in two small projections: one broader, leaf-like, strongly curved ventrad, the other one like a small tooth (t) (Fig. 8 C View Figure 8 ). Prostatic groove runs along medio-ventral side of acropodite.

Female unknown.

Remarks.

Sesoko-jima is a small island (area less than 3 km 2) very close to Okinawa-jima Isl., and it is somewhat surprising that it holds an endemic species of millipede. The species seems to be restricted to a small forest on the island.

Etymology.

Named after the type locality, Sesoko-jima Island, connected by bridge to the island of Okinawa-jima Isl .. Adjective, masculine.