Xystodesmus pallidus

Xystodesmus pallidus (Verhoeff, 1937) Figs 1–2, 10A, 12A–B, 15–16 Koreoaria pallida Verhoeff, 1937: 319–320, fig. 8. Koreoaria pallida – Tanabe & Shinohara 1996: 1487 (“species possibly belonging to Xystodesmus ”). — Lim 2001: 128–129, figs 142–144. — Marek et al. 2014: 71. Xystodesmus pallidus – Korsós & Nakamura 2025: 216–218, figs 11a–e, 12a–d, 13a–b. Diagnosis A small-sized (total body length up to 30 mm) Xystodesmus showing a typical colour pattern with orange or yellow paranotal spots. Differs from congeners by strongly separated femoral and tibiotarsal parts of the male acropodite (Fig. 2: a), a curved and pointed solenomere (Fig. 2: sl), and a simple, flat prefemoral process (Fig. 2: pfp). Type material Holotype SOUTH KOREA • ♂; “Südkorea”; SNSB-ZSM Reg.Nr. A20060019, SNSB-ZSM Reg.Nr. A20033594 (gonopods and legs, respectively). Paratypes SOUTH KOREA • 4 ♀♀; SNSB-ZSM Reg.Nr. A20060019. Other material examined SOUTH KOREA • 1 ♂; Gyeongsangnam Prov., Gimhae District, Daecheong Town, Mt. Bulmo-san; 35°10′42.4″ N, 128°45′11.6″ E; 9 Apr. 2023; D. Kim leg.; GenBank nos: PX471584 (COI), PX516894 (EF1-α) LEGOA030010 GH01 • 1 ♂; Gyeongsangnam Prov., Geoje District, Mundong Town, Mundong Recreational forest; 34°51′38.7″ N, 128°40′2.0″ E; 14 May 2023; D. Kim leg.; GenBank nos: PV446385 (COI), PV544250 (EF1-α); HNHM diplo-04554 GJ01 23 • 1 ♂; same data as for preceding; GenBank nos: PV446388 (COI), PV544253 (EF1-α); LEGOA030011 GJ04 23 • 1 ♂; Gangwon Prov., Taebaek District, Won Town; 37°17′04.1″ N, 128°57′17.8″ E; 959 m a.s.l.; 4 Jun. 2023, S.J. Suh leg.; LEGOA030012 TB05 • 1 ♂; Gangwon Prov., Taebaek District, Hwangji Town; 37°08′52.2″ N, 128°58′17.1″ E; 740 m a.s.l.; 4 Jun. 2023; S.J. Suh leg.; LEGOA030013 TB08 • 1 ♂; Gyeongsangnam Prov., Geoje District, Mundong Town, Mundong Recreational forest; 34°51′42.9″ N, 128°40′6.4″ E; 19 May 2024; G. Kim and D. Kim leg.; GenBank nos: PV446389 (COI), PV544254 (EF1-α); LEGOA030014 GJ01 24 • 1 ♂; same data as for preceding; GenBank nos: PV446390 (COI), PV544255 (EF1-α); LEGOA030015 GJ02 24 • 1 ♂; same data as for preceding; GenBank nos: PV446391 (COI), PV544256 (EF1-α); LEGOA030016 GJ03 24 • 1 ♂; same data as for preceding; LEGOA030017 GJ04 24 • 1 ♂; same data as for preceding; LEGOA030018 GJ05 24 • 1 ♂; same data as for preceding; LEGOA030019 GJ06 24 • 1 ♂; same data as for preceding; LEGOA030020 GJ09 24 • 1 ♀; same data as for preceding; HNHM diplo-04555 GJ08 24 • 1 ♂; Jellanam Prov., Damyang District, Wolsan-myeon, Yongheung-ri San 86-26; 35°20′22.9″ N, 126°53′25.8″ E; 6 Jul. 2024; G. Kim leg.; GenBank nos: PV446406 (COI), PV544271 (EF1-α); LEGOA030022 DY08 • 1 ♀; same data as for preceding; GenBank nos: PV446405 (COI), PV544270 (EF1-α); LEGOA030021 DY07. Description HEAD. Smooth, with 1+1 frontal setae and several smaller ones on clypeus and around antennal sockets; epicranial suture distinct. Antennae bent, article 1 globose, 2 long and clavate, articles 3–5 subequal in length, 6 longest, all setose, 7 small, length equal to width, with 4 apical sensory cones. COLLUM. Convex, oval, its length twice as long as metatergite 2, lateral edges pointed, anterior margin circular, with visible ridge, posterior margin straight with lateral parts directed forward (Fig. 12A–B). BODY. Collum and first four rings narrower, gradually widening to ring 5, body sides between rings 5–15 parallel, then gradually tapering towards telson. Proterga and metaterga completely smooth, metaterga with a transverse depression in the middle, without any tubercles or punctation. Posteriolateral edge of paranota 2–4 rectangular, of 5–6 slightly pointed, from 7 onwards triangular in shape, with weak excavation on the posterior edge of each of the metaterga. Pore formula mostly typical for Polydesmida, pores on rings 5, 7, 9, 10, 12–13, and 15–19, positioned laterally on slightly swollen paranota. Rings 16–19 gradually tapering, posterolateral projections becoming more pointed, on 17 triangular, on 18–19 very long, almost as long as length of metaterga. TELSON. Epiproct protruding, in dorsal view triangular and rounded, in lateral view slightly curved downwards, with 4+4 setae sitting on tubercles of sides, and with 2+2 stronger setae apically. Paraprocts (anal valves) smooth, with 2+2 setae on median ridges; hypoproct semitriangular, with 1+1 setae on small tubercles. LEGS. Bases of midbody legpairs well separated in males by 1.2–1.9 mm, in females by 1.7–1.8 mm, sterna smooth and wide, pro- and metasterna well separated. Coxae of legs from ring 7 short, its length subequal to prefemur, which has a well-developed ventral spine, increasingly larger from legs 9 onwards; femur 1.2 times as long as prefemur, slightly clavate; postfemur short, about ⅓ as long as femur; tibia subequal to postfemur, hairy, about same length as tarsus; podomeres distally increasingly hairy; curved claws on all legs. MEASUREMENTS. Males (based on 13 specimens): total body length 26–30 mm, midbody width (including paranota) 4.0– 6.6 mm, metatergal length 1.0– 1.6 mm, midbody prozonite width 2.8–4.2 mm, collum width 3.5–4.9 mm, median collum length 1.5–2.7 mm. Females (based on 2 specimens): total body length 27–29 mm, midbody width (including paranota) 5.5–6.4 mm, metatergal length 1.3–1.4 mm, midbody prozonite width 4.1 mm, collum width 4.4 mm, median collum length 1.9–2.1 mm. COLOURATION (Fig. 12A–B). Preserved specimens in ethanol with prozonite and metazonite dorsally equally brown, collum anteriorly with dark stripe, epiproct lighter; all metaterga paramedially with large, marbled patches, adjacent paranota with pale orange or yellow spots, first and last rings excluded. Head brown, antennae, legs, and ventral side light brown, whitish. MALE CHARACTERS. Coxae of legpairs 2–6 with pair of protruding, cone-shaped processes, those of legpairs 3 and 6 much reduced, those of legpairs 4–5 longer and pointed. Remaining legs and sterna without modifications. Gonopods (Figs 1B–C, 2A–F): with two conspicuous processes, prefemoral process (pfp), and acropodite (a), which is divided into femoral and tibiotarsal parts (solenomere, sl) by a cingulum (c). Coxa (cx) stout, subcylindrical, about twice as long as wide, without coxal apophysis, but with single apophyseal macroseta (ms) on dorsal side. Cannula on mesal side, starting near macroseta, then connected to prefemur and continuing in prostatic groove (pg). Prefemur short, stout, bent dorsad, densely setose; prefemoral process (pfp) thin and flat, parallel and subequal in length to femoral part of acropodite, shape variable, sometimes straight and apical part blunt, sometimes slightly bent ventrad and pointed. Acropodite (a) continuing from prefemur until a strong contraction called cingulum (see also Marek et al. 2014: 5, fig. 2b–c: cg). This part considered as femur, densely setose, slightly tapering distally, and with a parallel lamina along dorsal side. Tibiotarsal part (solenomere, sl) of acropodite starting after cingulum with thickening, then gradually tapering to pointed tip, which is strongly curved back toward prefemoral process. Prostatic groove (pg) runs dorsally on mesal side. FEMALE CHARACTERS. Somatic characters similar to those of males, including shape of collum, tergites and epiproct, as well as strong prefemoral ventral spines, starting on legpair 5. Coxae of legpair 2 with protruding, pointed processes (Fig. 10A), similar to males, but subsequent legs without any sternal or coxal modifications. Cyphopods in situ closely behind legpair 2, in joint transversal, semicircular-shaped opening; valves (v) of equal size, ventral edges jagged, medially with depression for genital opening, operculum (op) laterally closely overlaying, receptacles (r) deeply embedded under valves. Distribution Xystodesmus pallidus occurs in scattered locations across the entire South Korean Peninsula (Fig. 15). Remarks Xystodesmus pallidus was originally described by Verhoeff (1937) as Koreoaria pallida, the type species of the genus Koreoaria Verhoeff, 1937. When erecting the genus, Verhoeff (1937: 319) compared it to Pachydesmus Cook, 1895, at that time considered a large genus of the family Leptodesmidae (Attems 1938). The family was later divided into several families including Xystodesmidae (Hoffman 1978a, 1978b, 1980). Koreoaria pallida, together with its sister species K. amoena Takakuwa, 1942, was recently transferred to Xystodesmus, based only on the original description and examination of its type specimen (Korsós & Nakamura 2025). Having been able to investigate a relatively large number of specimens from different parts of South Korea, we became convinced that the specimens we studied are conspecific with Verhoeff’s “ pallida ”. The diagnostic separation of the femoral and tibiotarsal part by a cingulum in the male gonopod acropodite can also be observed in the microscopic slides made by Verhoeff (Fig. 1A–C), although the direction of the solenomere has changed to that of a right angle, probably due to the pressure of the microscopic cover glass. In all other aspects, our specimens morphologically agree with the original description, so the identification seems to be well warranted.