Xystodesmus variatus ( Pocock, 1895 ), 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 variatus ( Pocock, 1895) comb. nov.

Figs 9 A – 9 , 4 D , 17 A, B

Fontaria variata Pocock, 1895: 361, figs 15, 15 a; “ Great Loo-Choo (Holst Coll.) ” (= Okinawa)

Rhysodesmus variatus : Takakuwa 1954: 62

Riukiaria variata : Hoffman 1949: 5; Shinohara 1977: 118 (listed)

Riukiaria variata : Tanabe and Shinohara 1996: 1487 (“ species possibly belonging to Xystodesmus ”)

Riukiaria variata : Marek et al. 2014: 78

Type material examined.

Holotype (Fig. 9 D 39): • male, labeled as: “ 1892.10.10.51 , Gr. Loo-Choo , purchased of H. Seebohm ” ( NHMUK) .

Additional material examined.

• 1 male, Japan, Central Ryukyus, Okinawa Pref., Okinawa-jima Isl., Nakijin-son, Nakijin Village , 30 January 1996, leg. K. Yahata ( NSMT -My 547 ) ; • 2 males, Japan, Central Ryukyus, Okinawa Pref., Okinawa Group, Okinawa-jima Isl., Ogimi Village , limestone hill near Mt. Nekumachiji-dake, 26°41.0'N, 128°08.1'E, 250 m a. s. l., 24 January 2009, leg. R., P., and Z. Korsós ( HNHM diplo-04547 ) ; • 1 male, 4 females, Japan, Central Ryukyus, Okinawa Pref., Okinawa Group, Kouri-jima Isl. , limestone hill, 26°42'08.6"N, 128°00'38.5"E, 40 m a. s. l., 30 January 2010, leg. R., P., and Z. Korsós ( RUMF -ZD-00937 ) ; • 2 males, 3 females, Japan, Central Ryukyus, Okinawa Pref., Okinawa Group, Kouri-jima Isl. , limestone hill, 26°42'08.6"N, 128°00'38.5"E, 50 m a. s. l., 18 April 2010, leg. Z. Korsós (1 female HNHM diplo-04548 ; 1 male, 1 female VMNH; 1 male, 1 female NHMD 1184734 ) .

Diagnosis.

Small Xystodesmus with typical colour pattern still visible on preserved specimens, metaterga darker, proterga and paranota paler. Gonopod has only two branches, similar to X. parvus sp. nov. and X. rebekae sp. nov., but X. parvus sp. nov. is much smaller, and in X. rebekae sp. nov. both prefemoral process and acropodite are slender and straight, whereas in X. variatus comb. nov. they are strongly pointed and sickle-shaped in mesal view.

Description.

Measurements: length 29 mm, midbody segment width: 6.2 mm, metatergal length 2 mm; collum width 4.7 mm, median collum length 2.2 mm. Measurements of new material: length 24–29 mm, midbody segment width: 5.4–6.0 mm, metatergal length 1.2–1.4 mm; collum width 4.2–4.7 mm, median collum length 1.6–1.9 mm. Body sides between segments 5–15 parallel.

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

Pro- and metaterga smooth, transverse depression on metaterga hardly noticeable. Collum in dorsal view elongated sub-hexagonal, with weak marginal ridges all around, lateral corners directed posterio-ventrad, weakly pointed, posterior margin wavy. Anterior edges of all paranota rounded, posterio-lateral corners increasingly pointed caudad, from segment 5 onwards with a concave posterior excision. Lateral sides of paranota arched, those bearing pores depressed, pore formula normal.

Segments 15–19 gradually tapering, caudal corners becoming more pointed. Epiproct protruding, in lateral view slightly curved, slender, with 2 + 2 apical and 4 + 4 lateral setae all on strong tubercles; paraprocts smooth, with two pairs of setae, upper ones on margins, lower ones on sides; hypoproct semicircular with 1 + 1 setae on small tubercles.

Bases of midbody leg pairs well separated (by 1.0– 1.2 mm in male, 1.5–1.7 mm in females), sterna smooth and wide, pro- and metasterna fused together. Coxa ~ 2 × as long as wide; prefemur ~ 1.5 × longer, with well-developed ventral spine; femur 1.5 × longer than coxa, clavate; postfemur shorter than coxa, approximately as long as wide, tibia and tarsus slender, tarsus ~ 1.5 × longer than tibia; claw small, slightly curved ventrad.

Colour of newly collected living specimens (Fig. 17 A, B ) generally greyish, blueish brown with orange or yellowish paranotal spots. These are less conspicuous than in other Xystodesmus species (e. g., in X. kumamotoensis sp. nov. or X. rebekae sp. nov.). Proterga and sides of metaterga paler, more greyish, and in most cases a dark dorsomedial line also traceable, at least in midbody region. Preserved specimens lost colouration, but differences between pro- and metaterga, and the metatergal side spots still visible. Clypeus and epiproct pale brownish, underside of head, antennae, legs, and whole ventral side pale whitish.

Male sexual characters. Second leg pair with small coxal processes provided with three or four strong setae (as in X. parvus sp. nov., Fig. 6 D ), sterna of segments 4–6 and further legs without any modifications. Gonopods (Fig. 9 A – C ): Coxa stout, approximately as long as wide, coxal apophysis completely lacking, apophyseal macroseta (ms) relatively small. Prefemur short, sub-globose, densely setose on ventral side, setosity goes on to halfway of acropodite; prefemoral process (pfp) slender, curved ventrad, ~ ¾ as long as acropodite, ending in a long, pointed tip; acropodite (a) slightly broader at base, gradually tapering towards pointed tip, but subapically with a leaf-like broadening (l), in mesal view similar to an eagle’s claw (Fig. 9 A ). Prostatic groove runs along the mesal side of acropodite to the pointed tip.

Female sexual characters. Cyphopods (Fig. 10 ) deeply embedded in joint aperture closely behind leg pair 2, encapsulated in separate vulval sacs. Receptacula (r) on both anterior and posterior side, low, subtriangular, setose on entire surface; operculum (op) narrow, ~ ¾ as high as bursal valves; valves (v) rectangular, laterally with small projected tips, with several row of short setae along margins.

Remarks.

With the re-examination and the side-by-side comparison of the type specimens of Fontaria variata Pocock, 1895 and the freshly acquired specimens it became clear that they were conspecific. In the original description the colour, obviously based on preserved specimens, is described as “ upper surface rather thickly clouded with fuscous, with a clearer spot on each side above the keels ” ( Pocock 1895: 361); and those spots correspond to the orange paranotal spots observed on the living specimens. The body size, the shape and structure of metaterga and paranota, and especially the gonopods are in complete agreement in both samples, so the assignment of F. variata to Xystodesmus is justified.

Hoffman (1949) placed F. variata in Riukiaria together with F. holstii Pocock, 1895 , but Tanabe and Shinohara (1996) tentatively separated them in different genera, assigning variatus “ possibly ” to Xystodesmus . In the last part of their paragraph, Tanabe and Shinohara (1996: 1487), perhaps due to a typographical error, referred to variatus together with other species described by Takakuwa, saying that “ Rhysodesmus spinosissumus (recte spinosissimus ), Riukiaria geniculata , Ri. spiralipes , Ri. variata , K. amoea (recte amoena ), and Pachydesmus bazanensis , their types, which had been deposited in Y. Miyosi’s private collection, were destroyed in 1945 ”. However, R. variata was actually described by Pocock (1895), not Takakuwa, and its type has never been in Miyosi’s private collection, but has been stored and was recently found in the Natural History Museum, London, and is redescribed. The newly collected specimens were found in association with Riukiaria holstii ( Pocock, 1895) , a widespread species on the central and northern part of Okinawa-jima Island. This long-known species has also been recorded from more southwestern and remote islands in the Ryukyu Archipelago, such as Ishigaki-jima and Iriomote-jima in the Yaeyama Group and Uotsuri-jima in the Senkaku Group ( Nakamura and Korsós 2010). However, from our extensive myriapodological surveys conducted in the archipelago, we can say with near certainty that these records should be regarded as misidentifications. There are superficially similar species such as Riukiaria chelifera (Takakuwa, 1941) , endemic to the Yaeyama Group. The “ Rhysodesmus variatus ” found on Uotsuri-jima Island ( Ikehara and Shimojana 1971) may be an undescribed species due to the biogeographic peculiarities of the terrestrial faunas in the Senkaku Group among Japanese islands ( Ota 1998; Kurita et al. 2017).

Figures

Figure 4. Xystodesmus kumamotoensis sp. nov. A, B male paratype from Yatsushiro, Kumamoto Pref. A sterna of 4 th segment, anterior view B sterna of 5 th segment, anterior view C cyphopods of female paratype from Yatsushiro, Kumamoto Pref., posterior view. Abbreviations: op = operculum, r = receptacle, v = valve. Scale bars: 1 mm (A, B); 0.5 mm (C).

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 9. Xystodesmus variatus (Pocock, 1895) comb. nov. A, B right gonopod of male from Kouri-jima Isl., Okinawa Pref., mesal and lateral views, respectively. C original figures by Pocock (1895), “ fig. 15. Fontaria variata. Left copulatory foot from below, fig. 15 a. Ditto, outer view. ” D Fontaria variata Pocock, 1895, holotype male specimen (BMNH, Reg. Nr. 1892.10. 10.51). Abbreviations: a = acropodite, ms = macroseta, l = lobe, pfp = prefemoral process. Scale bar: 1 mm (A, B).

Figure 10. Xystodesmus variatus (Pocock, 1895), comb. nov. Left cyphopod of female from Kouri-jima Isl., Okinawa Pref., anterior view. Abbreviations: op = operculum, r = receptacle, v = valve. Scale bar 0.5 mm.

Figure 17. Live habitus of Xystodesmus millipedes A, B X. variatus (Pocock, 1895) males, Kouri-jima Isl., Okinawa Pref. C, D X. martensii (Peters, 1864) males C Eno-shima Isl., Kanagawa Pref. D Mt. Oyama, Kanagawa Pref. E, F X. nikkoensis (Chamberlin & Wang, 1953) males, Yaku-shima Isl., Kagoshima Pref. Not to scale.