Xystodesmus fasciatus, Korsós & Nakamura, 2025

Xystodesmus fasciatus sp. nov.

Figs 1 A – F View Figure 1 , 16 A View Figure 16

Type material.

Holotype: • male, Japan, Kyushu, Kagoshima Pref., Satsuma Peninsula, Hioki City, Fukiage Town, Yokura , Cryptomeria japonica plantation, 15 m a. s. l., 31°30'46.4"N, 130°22'31.1"E, 14 October 2009, leg. Z. Korsós and Y. Nakamura ( NSMT -My 534 ) GoogleMaps . Paratypes: • 1 male, and 1 juv. male, same locality and date as holotype ( HNHM diplo-04540 ) GoogleMaps . 2 males, same locality and data as holotype ( RUMF -ZD-00952 and 00953) GoogleMaps .

Diagnosis.

Medium-sized Xystodesmus species showing the general colour pattern plus a dark dorsal transversely banded appearance. Metatergites are smooth, shine, in contrast to that of X. martensii where they are conspicuously tuberculate. In terms of gonopods, the most similar species is X. martensii which also has a strong coxal apophysis, but in X. fasciatus sp. nov. it is almost hook-like; prefemoral process flat and wide, curving backwards, in X. martensii it is slender and straight. Acropodite with three small teeth at tip, whereas in X. martensii it has a cup-shaped process. X. yamamiensis has also a strong coxal apophysis, but its acropodite is strongly bifurcated and its prefemoral process is slender and tapering.

Description

(based on the two adult male specimens). Length 32–33 mm, midbody width with paranota 5.8 mm, metatergal length 1.9 mm, collum width 4.9 mm, median collum length 3.1 mm. Body sides between segments 5–13 parallel. Head smooth, with 1 + 1 frontal setae, epicranial suture distinct. Antennae straight, slender, first article globose, articles 2–4 subequal in length, 5 and 6 increasingly longer, 7 small, with length equal to width. Proterga completely smooth, metaterga very weakly wrinkled, each with a transverse depression in the middle. No trace of tubercles or punctation on metaterga. Collum subtrapezoid-shape, convex, its length double of metatergum 2, lateral edges directed ventrad, anteriolateral margin with weak ridge. Posteriolateral edge of paranota 2 and 3 rounded, of 4 slightly pointed, from 5 onwards triangular shaped, with strong half-circle excavation on the posterior edge of each metaterga. Pore formula normal, pores on segments 5, 7, 9, 10, 12, 13, 15, 16, 17, and 18, in lateral position on slightly swollen paranota.

Segments 14–19 gradually tapering, posteriolateral projections becoming more pointed, with strong excavations along their mesal side. Epiproct protruding, in lateral view distinctly curved, with two pairs of setae on small side tubercles, and with two setae apically; paraprocts (anal valves) smooth, with a pair of setae on obvious median ridges; hypoproct semicircular.

Bases of midbody leg pairs well separated (by 1.6 mm), sterna smooth and wide, pro- and metasterna well separated. Prefemur with well-developed ventral spine, increasingly larger from midbody legs onwards, femur ~ 2 × as long as prefemur, almost straight, postfemur short and incrassate, tibia slender, long, nearly as long as tarsus, claw on pregonopodal legs flattened and curved, leaf-like, becoming normal on other legs towards the end of body.

Colour of living specimens on dorsal side vividly banded as a result of alternating pale greyish prozona and dark chocolate-brown metazona (Fig. 16 A View Figure 16 ). Collum pale greyish in the middle and bordered with dark brown. Dark brown median stripe on dorsum from 4 th segments onward. Paranota bright reddish orange. Clypeus light brownish, underside of head, antennae, legs, epiproct, and whole ventral side pale, almost whitish. Colour in alcohol quickly bleaches, only the dorsal dark banded pattern remains visible.

Male sexual characters. Sterna of segments 3 and 4 (Fig. 1 E, F View Figure 1 ) with a pair of protruding processes, on segment 3 small, widely separated from each other, with long apical setae; on segment 4 nearly as high as width of coxae, closely packed to each other, with short setae. Second leg pair with low but definite, blunt coxal processes (Fig. 1 C View Figure 1 ). Other legs and sterna without extra modifications. Gonopods (Fig. 1 A, B View Figure 1 ): Basically composed of two conspicuous processes, one considered as prefemoral process (pfp), and one as acropodite (a). Coxa strong, stout, nearly as long as wide, with well-developed, hook-like apophysis (ca) on its anteriomesal shoulder, and a large single apophyseal seta (ms). Prefemur stout, bent dorsad, densely setose, prefemoral process broad and flat, like a lamella, abruptly tapering to its tip which is pointed and curved backwards, in the direction of the coxal apophysis. Acropodite setose up to 2 / 3 of its length, gradually tapering towards its tip which is bent mesad, and terminates in two pointed branches connected to each other by a transparent, thin plate. At approximately the separation point of the two tips on the lateral side a small, there is a pointed process like a spur. Prostatic groove runs along the dorsomesal edge of the acropodite.

Female unknown.

Remarks.

The specimens were found in planted and managed Cryptomeria japonica forest, in the deeper layers of mulch, in association with another xystodesmine millipede, Riukiaria cornuta ( Haga, 1968) .

Etymology.

To emphasise the transversely banded appearance (= fasciatus, in Latin). Adjective, masculine.