A revision of the millipede genus Riukiupeltis Verhoeff, 1939 (Diplopoda, Polydesmida, Paradoxosomatidae), with comments on the status of related species

Abstract The East Asian millipede genus Riukiupeltis Verhoeff, 1939 is revised, and is restricted to a single species, Riukiupeltis jamashinai Verhoeff, 1939. Examination of the type specimens and freshly collected material from the Ryukyu Archipelago and Vietnam show that both subsequently allocated species, Riukiupeltis uenoi Murakami, 1975, and Riukiupeltis falcatus (originally Haplogonosoma falcatum Attems, 1953, reallocated by Jeekel 1968), do not belong to this genus; moreover, they are not even congeneric with each other. According to our morphological observations, including the gonopods, Riukiupeltis uenoi is closer to the widespread Chamberlinius hualienensis Wang, 1956, hence we propose the new combination Chamberlinius uenoi (Murakami, 1975), comb. n. Riukiupeltis falcatus, on the other hand, represents a separate, as yet monotypic, genus Simplogonomorpha gen. n., distinct both from Haplogonosoma Brölemann, 1916 sensu Golovatch et al. (1995), and from Verhoeff’s original Riukiupeltis. Additionally, Simplogonomorpha falcata (Attems, 1953), comb. n is re-described here based on fresh material from Vietnam. A key and colour habitus-illustrations to all three species are also provided here.


introduction
The millipede genus Riukiupeltis was established for a single species R. jamashinai by Verhoeff, 1939 from the Ryukyu island Miyako, Japan (Riukiu and Mijako, in German). Jeekel (1968) referred to the genus in his monograph on the distribution of the family Paradoxosomatidae, and placed it in the tribe Tonkinosomatini. Moreover, he also tentatively allocated the species Haplogonosoma falcatum Attems, 1953, described from Xieng Khoang, Laos, to Riukiupeltis. Murakami (1975 described a new species Riukiupeltis uenoi from Sabichi-go Cave, Ishigaki-jima island, the Ryukyus. Therefore, altogether three species have been assigned to Riukiupeltis. The genus belongs to the tribe Chamberlinini, together with Aponedyopus Verhoeff, 1939, Chamberlinius Wang, 1956, Geniculodesmus Chen, Golovatch and Chang, 2008, and Haplogonosoma Brölemann, 1916(Chen et al. 2011. Following several discussions on the genus in the past (Jeekel 1968, Hoffman 1973, Murakami 1975, Chen et al. 2011), its status is still dubious, so our purpose here is to provide a revision of the genus based on fresh material and type specimens.

Material and Methods
Fresh material of Riukiupeltis falcatus (Attems, 1953) and R. uenoi Murakami, 1975 was collected from Bi Doup National Park, Lam Dong province, Vietnam, and Iriomote-jima and Ishigaki-jima islands, the Ryukyu Archipelago, Japan, respectively. The type specimen of R. jamashinai was studied as a loan from the Bavarian State Collection of Zoology, Munich, Germany (BSCZ), whereas the holotype of R. uenoi was borrowed from the National Museum of Nature and Science, Tokyo (NMNS). Further material is shared between the University Museum (Fujukan) of the University of the Ryukyus, Okinawa (RUMF), the Hungarian Natural History Museum, Budapest (HNHM), and the Institute of Ecology and Biological Resources (IEBR), Hanoi, Vietnam. In addition, new material of R. jamashinai was identified in the collection by M. Shimojana, acquired in 1979 on Miyako-jima island.
Line drawings were made by using an Olympus SZX10 (ADN), and a Leica M125 (ZK) stereo microscope with drawing tube attached. SEM images were made by using a Hitachi S4800 scanning electron microscope. Colour photographs were taken by ZK using a Nikon D90 digital camera with macro lens and Leica microscope photo tube attached. The distribution map was generated using the software DIVA-GIS version 7.0. Diagnosis. Gonofemorite strongly curved, distal part somewhat swollen and membraneous. Postfemoral region demarcated from femorite by obvious cingulum, and bent continuously forming almost a complete circle with femorite. Postfemoral regions consisting of a thick, strong and free solenomere, and an extremely short solenophore (= tibiotarsus). Type species. Riukiupeltis jamashinai Verhoeff, 1939 Remarks. This genus is relatively close to the genus Chamberlinius Wang, 1956, however, it definitely differs in gonopod conformation: femorite without lamina; solenophore very short, thick, and without any basal processes. Verhoeff, 1939 http://species-id.net/wiki/Riukiupeltis_jamashinai  Distribution. Japan, Ryukyu Archipelago, Miyako-jima island. Remarks. Although after the description of R. jamashinai in 1939, Jeekel (1968) and Hoffman (1973) commented that gonopod tibiotarsus is missing in this species, Verhoeff's line drawing clearly shows it as depicted from the slide preparation ( Fig.  1). Re-examining the type specimen and the slide of the gonopod, as well as studying newly identified specimens found in Shimojana's collection, we are able to confirm that a gonopod tibiotarsus (=solenophore, sph in Fig. 2) is present, although it is small and closely attached to solenomere (sl in Fig. 2). (Murakami, 1975 Riukiupeltis uenoi:-Nakamura and Korsós 2010: Acta Arachnologica 59 (2) (Murakami, 1975) comb. n., left gonopod of male Mt. Banna-dake, Ishigaki-jima Island A dorso-mesal view B lateral view. (l = lamina, c = cingulum, sl = solenomere, sph = solenophore or tibiotarsal process, lp = laminar process, pp = pointed process)). Scale bar = 0.5 mm.

Chamberlinius uenoi
Remarks. Murakami (1975) when describing the species commented that the terminal portion of the gonopod is more complicated than that of Riukiupeltis jamashinai Verhoeff, 1939. He also agreed with Verhoeff, 1939 in its configuration, and placed his species in Riukiupeltis. However, the species uenoi, in fact, differs largely from the type species R. jamashinai in gonopod conformation.
After studying the type and freshly collected specimens, it became clear that the species uenoi is strongly different from Riukiupeltis jamashinai in its gonofemorite having a long lamina l, and a longer solenophore with basal processes pp and lp (Fig 3). We found that this species is more similar to Chamberlinius hualienensis Wang, 1956. Both Ch. hualienensis and Ch. uenoi comb. n. have well-developed paraterga (Figs 7A-B), large, slender and strongly concave gonofemorite, with a lamina at the mesal side (l in Fig. 3). Postfemoral region is demarcated from femorite by obvious cingulum (c in Fig. 3), and includes a long and large solenomere (sl) reaching femur, and a shorter solenophore (sph) with a basal lobe. However, the two species differ from each other in the length of the postfemoral processes, by the shape of the small basal processes on the solenophore, and by live colouration. The dark brown, transversal metatergal bands in Ch. uenoi comb. n. are not divided by a median light brown longitudinal line (Figs 7C, 8C) as in Ch. hualienensis (Figs 7B, 8B). Moreover, Ch. uenoi comb. n. is strictly confined to undisturbed, natural evergreen broadleaf forests, and can only be found deep in decaying dead wood, whereas Ch. hualienensis has a strong tendency for being synanthropic, and dispersed in large numbers onto many islands (especially in the southern part of Japan) by human activities.
Etymology. A feminine noun to emphasize the simple gonopod conformation. Remarks. Jeekel (1968) in his classification of the family Paradoxosomatidae stated that "It appears that in Riukiupeltis the gonopod tiobiotarsus is also completely lost, although Verhoeff was of a different opinion when he described jamashinai". He believed that the gonopod tibiotarsus (= solenophore) was lost in Riukiupeltis, so he transferred Attems's species Haplogonosoma falcatum to this genus.
In fact, the solenophore of R. jamashinai still exists, although short, and somewhat hidden next to the solenomere, whereas solenophore of Simplogonomorpha gen. n. is totally missing. A comparison of genera in the tribe Chamberlinini is provided in Table 1. Remarks. New material does not much differ from Attems's description. Only minor difference is the presence of two separate cones between coxae 4 instead of only one small conal process in Attems's description. Recently, Chen et al. (2011) also published an illustration of gonopods of Haplogonosoma falcatum collected from the same locality, BiDoup National Park, Vietnam. Our material here fits well with their unevaluated illustration.  (Attems, 1953) comb. n. from Vietnam, BiDoup National Park A 10 th body segment, dorsal view B sternal processes between 4 th coxae, posteriovenral view C leg 10, lateral view D telson, ventral view e-G right gonopod e mesal F lateral, and G subdorsal view. Scale bar = 1 mm.

Figure 5.
Simplogonomorpha falcata (Attems, 1953) comb. n. from Vietnam, BiDoup National Park, right gonopod: ventral A and mesoventral view B, C Tip of gonopod, ventral view D. Gonofemorite large, slender and strongly concave, with a lamina on the mesal side. Postfemoral region with a long, large solenomere and a shorter solenophore, the latter basally with two processes, a laminar mesal (lp) and a more pointed lateral one (pp) (Fig. 3B)    -Gonofemorite only slightly curved, with a weak dorsal lamina, distal part swollen and membraneous. Postfemoral region consisting a thick, strong, free solenomere, and a short, somewhat hidden solenophore (Fig. 2) .......Riukiupeltis

Key to representatives to all three genera (based on male characters)
In the key above, Riukiupeltis and Simplogonomorpha are represented by only one species each (jamashinai and falcata, respectively). Chamberlinius, on the other hand, includes at present five species: Ch. hualienensis, Ch. piceofasciatus, Ch. pessior, Ch. sublaevus (all keyed already by Chen et al. 2011), and Ch. uenoi, as added here.