Xystodesmus rebekae, Korsós & Nakamura, 2025

Xystodesmus rebekae sp. nov.

Figs 7 A – D View Figure 7 , 16 E View Figure 16

Type material.

Holotype: • male, Japan, Central Ryukyus, Okinawa Pref., Okinawa Group, Okinawa-jima Isl., Motobu Peninsula, Mt. Yae-dake , 26°38'17.5"N, 127°55'37.9"E, 390 m a. s. l., 30 December 2009, leg. R. Korsós, Z. Korsós and Y. Nakamura ( NSMT -My 544 ) GoogleMaps . Paratypes: • 6 males and 2 females, same locality and date (1 male, 1 female NSMT -My 545 ; 1 male, 1 female RUMF -ZD-00943 , RUMF -ZD-00944 ; • 1 male HNHM diplo-04544 ; • 1 male VMNH 112447 , 1 male NHMD 1184733 ) GoogleMaps ; • 1 juv. male, same locality, 8 November 2010, leg. Z. Korsós and Y. Nakamura (No. 285) ( HNHM diplo-04545 ) GoogleMaps .

Diagnosis.

Medium to relatively large Xystodesmus with typical colour pattern, dark brown terga and bright orange paranotal spots. With its simple, two-branched male gonopod completely lacking coxal apophysis and sternal modifications on pregonopodal legs X. rebekae sp. nov. differs from all its congeners. Most similar species are X. variatus and X. gracilipes which also have only two gonopodal processes, but X. rebekae sp. nov. has a longer, S-shaped femoral process and a shorter, slimmer acropodite.

Description.

Length 29–33 mm, midbody width with paraterga 6.6–7.3 mm, midbody metatergal length 1.5–1.8 mm, collum width 5.3–5.8 mm, median collum length 2.5–2.7 mm. Body sides between segments 5–14 subparallel.

Head smooth, with two frontal setae, epicranial suture distinct. Antennal articles more-or-less straight, slender, first article sub-globose, articles 2 and 3 subequal in length, 4–6 also subequal but slightly longer than 2 and 3, 7 small, little wider than long.

Pro- and metaterga completely smooth, transverse depression in metaterga hardly noticeable, but on midbody segments with two weak lateral swellings. Collum subtrapezoidal, arched, ≤ 2 × longer than metatergum 2, lateral edges directed posterioventrad, anteriolateral margin with well visible ridge. Anterior edge of paranota 2–4 slightly rounded, almost right-angled, posterior edge rounded, without projection. Triangular projection behind on metaterga 5, from 6 onwards increasingly pointed, sublateral excavations on posterior margin of midbody segments already strong, semicircular. Lateral sides of paranota arched, outline of segments clearly delimited. Pore formula normal, pores in lateral central position on narrow paranota.

Segments 15–19 gradually tapering, posterior corners becoming more pointed. Epiproct protruding, in lateral view slightly curved, with two large setae on each lateral side on tubercles, projection with two pairs of setae on small side tubercles, two pairs in dorsolateral position, and 2 + 2 setae apically (8 pairs of setae altogether); paraprocts smooth, with two pair of setae on obvious median ridges; hypoproct subtrapezoidal with two setae on small tubercles.

Bases of midbody leg pairs well separated (by 1.3–1.5 mm), sterna smooth and wide, pro- and metasterna well separated. Coxa short, almost as wide as long; prefemur 1.2 × longer, on postgonopodal legs with well-developed ventral spine; femur 1.2 × longer than prefemur, slightly bent proximad; postfemur, tibia, and tarsus subequal in length, all ~ ½ as long as femur; claws normal on all legs.

Colour of living specimens (Fig. 16 E View Figure 16 ) generally dark brown appearance with bright orange paranotal spots. Proterga slightly paler, metaterga with two circular lateral spots. Preserved specimens paler, but the circular markings and the yellowish paranotal spots still noticeable. Clypeus pale brownish, underside of head, antennae, epiproct, and whole ventral side pale whitish, legs pale brown.

Male sexual characters. Second leg pair (Fig. 7 C View Figure 7 ) with small tubulous coxal processes, ~ 1 / 3 length of prefemora, sterna of segments 4–6 without any modifications (Fig. 7 D View Figure 7 ). Gonopods (Fig. 7 A, B View Figure 7 ): Coxa long and slender, ~ 2 × as long as wide, coxal apophysis completely lacking, only a single apophyseal macroseta (ms) on anteriomesal side. Prefemur slender, bottle-shaped, densely setose; prefemoral process (pfp) long, longer than acropodite, drawn S-shaped, smooth, without spines or spurs, gradually tapering and ending in a pointed tip. Acropodite (a) slim, subparallel-sided, ~ 2 / 3 in length of prefemoral process, slightly spatulate before pointed tip where prostatic groove opens. In situ both branches (acropodite and prefemoral process) directed ventromesad, and those of the two gonopods crossing each other.

Female sexual characters. Cyphopods deeply embedded in joint aperture closely behind leg pair 2, encapsulated in separate vulval sacs. Receptacula on both anterior and posterior side, subtriangular, setose on entire surface; operculum oval, narrow; valves round, without projected tips, with short setae along margins.

Remarks.

The individuals were collected in broad-leaved forest ground, always under loose stones. In the same habitat, but in the litter, Riukiaria holstii ( Pocock, 1895) and Riukiaria neptuna ( Pocock, 1895) were also found. X. rebekae sp. nov. seems to be confined to the single locality which is a limestone hill with medium altitude (350–400 m) (relatively high for Okinawa-jima Isl.).

Etymology.

Named after Rebeka Korsós, daughter of ZK, who found the first specimen in the type locality. Genitive noun derived as a matronym.