Genus Xystodesmus Cook, 1895

Takakuwaia Verhoeff, 1936 (with the type species T. furculigera Verhoeff, 1936): synonymised by Hoffman (1956)

Cyphonaria Verhoeff, 1936 (with the type species C. scabra Verhoeff, 1936): synonymised by Hoffman (1980)

Phrurodesmus Takakuwa, 1943 (with the type species P. gracilipes Takakuwa, 1943): synonymised by Tanabe and Shinohara (1996)

Nikkonus Chamberlin & Wang, 1953 (with the type species N. nikkoensis Chamberlin & Wang, 1953): synonymised by Tanabe and Shinohara (1996)

Koreoaria Verhoeff, 1937, syn. nov.

Type species by original designation.

Polydesmus (Fontaria) martensii Peters, 1864 .

Diagnosis.

The genus Xystodesmus, as a member of the tribe Xystodesmini, is characterised by the followings: small body size (less than 40 mm), posteriolateral corners of paranota usually acute, extending posteriorly beyond medial metatergal margin, presence of paranotal spots (red, orange, or yellow), and gonopods composed of coxa with prefemur and acropodite fused into a simple telopodite. In East Asia the tribe Xystodesmini is represented by five genera: Koreoaria Verhoeff, 1937 (herewith synonymised with Xystodesmus), Levizonus Attems, 1938, Riukiaria Attems, 1938, Xystodesmus, and Yaetakaria Hoffman, 1949 . From these, based on gonopods, the most similar genus to Xystodesmus is Riukiaria, which share a common male gonopodal plan, usually with two well-developed processes (Tanabe and Shinohara 1996; Korsós et al. 2011). Xystodesmus, however, has various additional gonopodal appendages, while those of Riukiaria have none or only a few (its gonopod is more-or-less forceps-like). We also consider that colouration of live specimens is distinctive, with respect to their bright paranotal spots. All xystodesmids are strongly fluorescent when illuminated with ultraviolet light. Although traditional taxonomy is primarily based on gonopod morphology (Marek et al. 2014), the separation of the two genera is also supported by molecular phylogeny (Means et al. 2021 b).

Koreoaria was introduced by Verhoeff (1937) with the South Korean species K. pallida (Verhoeff, 1937) . He compared the new genus to Pachydesmus Cook, 1895, based on the superficially similar gonopod conformation (Verhoeff 1937). Pachydesmus, however, proved to be a strictly North American genus (Hoffman 1958) in its own tribe Pachydesmini (Hoffman 1980), and Koreoaria was considered belonging to the East Asian members of Xystodesmini (Tanabe and Shinohara 1996; Korsós et al. 2011). A second species, Koreoaria amoena (Takakuwa, 1942) was described, also from South Korea, and both species were proposed as “ species possibly belonging to Xystodesmus ” (Tanabe and Shinohara 1996: 1487). Observing the overall similarity of the type material of the type species of Koreoaria, here we take the opportunity to formalise the synonymy under Xystodesmus .

Species and distribution of Xystodesmus

(in order of date of description):

X. martensii (Peters, 1864): Kanto and Chubu regions, Honshu, Japan (Peters 1864: 3 as Polydesmus martensii; Cook 1895: 5; Hoffman 1956: 97–99, figs 1–4; Tanabe and Shinohara 1996: 1480–1482, figs 2–9, 10 A – E, 11 A – E, 12 A, B, 14, 17 A – F)

X. variatus (Pocock, 1895), comb. nov.: Okinawa-jima Isl., Okinawa Pref., Japan (Pocock 1895: 361, figs 15, 15 a as Fontaria variata)

X. pallidus (Verhoeff, 1937), comb. nov.: South Korea (Verhoeff, 1937: 319–320, fig. 8 as Koreoaria pallida)

X. shirozui (Takakuwa, 1942): Tsushima and Iki Isl., also Danjo Isl. (Oshima, Meshima), Nagasaki Pref., Japan (Takakuwa 1942 a: 239, fig. 5 as Rhysodesmus shirozui; Takakuwa 1954: 63–64, fig. 65; Miyosi 1959: 80, fig. 55; Minato 1973: 127–128, fig. A; Tanabe and Shinohara 1996: 1485–1487, figs 11 M, N, 13 C, D, 16 C, D, 17 O, P)

X. amoenus (Takakuwa, 1942), comb. nov.: Daegu, South Korea (Takakuwa 1942 b: 362 –363, fig. 5 as Koreoaria amoena)

X. gracilipes (Takakuwa, 1943): Ehime Pref., Shikoku, Japan (Takakuwa 1943: 604–605, fig. 2 as Phrurodesmus gracilipes; Takakuwa 1954: 84–85, figs 93, 94; Murakami 1965: 165, figs 1, 2; Tanabe and Shinohara 1996: 1484–1485, figs 11 L, 13 B, 16 B, 17 K)

X. serrulatus (Miyosi, 1952): Central part of Honshu and Shikoku (Tokushima Pref.), Japan (Miyosi 1952: 281, fig. 1 as Rhysodesmus serrulatus; Tanabe and Shinohara 1996: 1483–1484, figs 10 G, 11 H, I, 12 D, 15 D – I, 17 I, J)

X. nikkoensis (Chamberlin & Wang, 1953): Yaku-shima Isl., Kagoshima Pref., Japan (the two type specimens from Honshu: Tochigi Pref., Nikko, are probably mislabeled) (Chamberlin and Wang 1953: 9, fig. 3 as Nikkonus nikkoensis; Tanabe and Shinohara 1996: 1484, figs 11 J, K, 13 A, 16 A, 17 L, M)

X. saltuosus (Haga, 1968), comb. nov.: Fukuoka Pref., Kyushu, Japan (Haga 1968 8, fig. 6 a – e as Rhysodesmus saltuosus)

X. tokaiensis Tanabe & Shinohara, 1996: Shizuoka Pref., Honshu, Japan (Tanabe and Shinohara 1996: 1482–1483, figs 1, 10 F, 11 F, G, 12 C, 15 A – C, 17 G, H)

X. yamamiensis Masuda, 2001: Aichi Pref., Honshu, Japan (Masuda 2001: 635–636, fig. 1 A – H)

X. fasciatus sp. nov.: Satsuma Peninsula, Kagoshima Pref., Kyushu, Japan

X. keramae sp. nov.: Aka-jima Isl. (possibly also Tokashiki-jima Isl.), Okinawa Pref., Japan

X. kumamotoensis sp. nov.: Kumamoto and Oita Pref., Kyushu, Japan

X. kumeensis sp. nov.: Kume-jima Isl., Okinawa Pref., Japan

X. parvus sp. nov.: Okinoerabu-jima Isl., Kagoshima Pref., Japan

X. rebekae sp. nov.: Okinawa-jima Isl., Okinawa Pref., Japan

X. sesokoensis sp. nov.: Sesoko-jima Isl., Okinawa Pref., Japan

From the species list above, we did not have the opportunity to examine specimens of four species, X. shirozui, X. gracilipes, X. serrulatus, and X. tokaiensis, all occurring on the main islands of Japan (Honshu, Shikoku, and Kyushu) and adjacent islands, because of the loss of type material and / or the lack of fresh specimens. Xystodesmus martensii and X. yamamiensis are also distributed in Honshu, but since we had freshly collected material and the type specimens, respectively, we could compare them to the other species and include them in our descriptions. For the former Korean genus Koreoaria, type material of K. pallida was available for comparison and redescription, but unfortunately the types of K. amoena could not be found; the majority of Y. Takakuwa’s material, kept after his death in 1960 by Y. Miyosi, is believed to have been lost after Miyosi’s death in 1995 (Tanabe and Shinohara 1996; Chao and Chang 2008). All the other Xystodesmus species in our review, including the new ones, occur in the southwestern part of Japan (Kagoshima and Okinawa prefectures).