Riukiaria mundyi, Korsós, Zoltán, Nakamura, Yasuyuki & Tanabe, Tsutomu, 2011

Korsós, Zoltán, Nakamura, Yasuyuki & Tanabe, Tsutomu, 2011, Two new millipede species of the genus Riukiaria (Diplopoda, Polydesmida, Xystodesmidae) endemic to the Ryukyu Archipelago, Japan, Zootaxa 2877, pp. 55-68 : 62-66

Riukiaria mundyi sp. n.

Figs 4–6, 14–19.

Holotype male (NSMT-My 379)— Japan, Southern Ryukyus, Yaeyama Group, Yonaguni-jima Island, Mt. Dunandake, primary forest, N24.4577° E122.9711°, 146 m alt., 31 August 2009, leg. Z. Korsós & Y. Nakamura.

Paratypes: 3 males, 5 females, 2 juvs. ( RUMF, HNHM)—Same locality and date.

1 male, 1 female ( RUMF)— Japan, Southern Ryukyus, Yaeyama Group, Yonaguni-jima Island, Adigara Cave area, near construction place, N24.4599° E122.9594°, 44 m alt., 2 September 2009, leg. Z. Korsós & Y. Nakamura

2 females (NSMT-My 380)— Japan, Southern Ryukyus, Yaeyama Group, Yonaguni-jima Island, Arakawabana forest trail, 134 m, primary forest, N24.4441° E123.0107°, 1 September 2009, leg. Z. Korsós & Y. Nakamura

4 males, 5 females, 3 juvs. ( RUMF, HNHM)— Japan, Southern Ryukyus, Yaeyama Group, Yonaguni-jima Island, Kubura-bari, N24°27.4’ E122°56.6’, 50 m alt., rocky grassland, 14 February 2010, leg. R. & Z. Korsós Diagnosis. A member of the genus Riukiaria as defined by Shinohara (1977) and Tanabe and Shinohara (1996) with the simple, forceps-like male gonopod conformation. It differs from congeners first of all by its coloration in life (almost uniformly pinkish-orange), by its exclusive occurrence on a single island (Yonaguni-jima), and in details of gonopod morphology.

FIGURES 14–16. Riukiaria mundyi sp. n. 14= Anterior body part paratype male, dorsal view; 15= Epiproct of paratype male, dorsal view; 16= Sternum, coxa, and prefemur of 2nd legpair of paratype male, posterior view. Scales 1 mm (14,15) and 0.5 mm (16).

Etymology. The specific epithet is a patronym in honor of Mr. Imre Mundy (Budapest), a Hungarian engineer, long time friend and supporter of the first author (genitive, masculine).

Description. Measurements: Body size generally smaller than in most other Riukiaria species. Length of males 36–42 mm, midbody paranotal width 7.5–8 mm, metatergal length 1.8–2 mm, collum width 6–6.6 mm, length 2.4–3 mm (n= 4). Female body length 36–41 mm, midbody paranotal width 7.8–8.6 mm, metatergal length 1.8–2 mm, collum width 6.3–7.1 mm, length 2.8–3.3 mm (n= 8). Kubura-bari population (see Remarks): Male body length 25–26 mm, midbody paranotal width 5.1–5.3 mm, metatergal length 1.2–1.3 mm, collum width 4.4– 4.6 mm, length 1.9–2.1 mm (n= 4). Female body length 30–31 mm, midbody paranotal width 6.3–6.8 mm, metatergal length 1.3–1.4 mm, collum width 5.2–5.5 mm, length 2.5–2.6 mm (n= 5).

Color in life (Fig. 4): Whole body is almost uniformly light orange, pinkish, occasionally tending toward reddish or dark yellowish. Head, prozona, legs, and underside paler, 6th segment of antennae, tibiae and tarsi whitish.

On collum and each metatergum a slightly darker, almost brownish median patch, pronounced towards paranota as oval spots. On preserved specimens (70% ethanol) the vivid color quickly disappears, only shadows of the abovementioned pattern remains. Coloration of males and females does not differ. Fluorescence in UV light strong (Figs 5–6), especially on prozona and underside, metazona are slightly greyish.

Head smooth, epicranial suture distinct, 2+2 frontal setae, several setae scattered above clypeus, with 2 dense rows at its margin and on labrum. Antennae straight, first article globose, 2nd slightly clavate, subequal with articles 3–5, 6th longest, about 1.2 x longer than 5th, 7th small, slender, slightly longer than wide. Gnathochilarial stipites and lamellae linguales covered densely with short hairs, large, triangular mentum with smaller, distinct, median hair-field.

Collum convex, smooth, shiny, lateral and posterior margin with weak ridge, lateral corners triangular, slightly directed caudad. Pro- and metaterga smooth without any traces of tubercles or punctuation, not even wrinkles. Posteriolateral edge of paranota 2–3 triangular, on 4th and onwards strongly pointed caudad (Fig. 14). Pore formula normal, pores on paranota 5,7,9,10,12,13,15,16,17, and 18, in median excavation of paranota (in lateral view). Sides between segments 6–13 perfectly parallel, segments 14–19 gradually tapering, posteriolateral projections become more pointed. Epiproct in dorsal view subtriangular (Fig. 15), in lateral view protruding over paraprocts, parallel-sided, slightly curved ventrad, with 7+7 setae, 3+3 of them sitting on knobs. Paraprocts strongly marginate with 2+2 setae, hypoproct with 1+1 setae on knobs.

Midbody legs well separated (by 1.8–1.9 mm in males, 2.4–2.8 mm in females), sterna wide and smooth. Postgonopodal legs with moderately developed ventral spine on prefemur, increasingly stronger towards body end, femur about twice as long as prefemur, straight, postfemur crassate, tibia straight, both subequal in length and about 1/3rd of femur, tarsus slender, about twice as long as tibia, claw (ca. 0.5 mm long) curved.

Sexual characters: Male 2nd legpair (Fig. 16) coxa with strong median projections about half as long as length of coxa, apically with membraneous tubules surrounded by strong setae, 1+1 macrosetae sitting at joint of prefemur (1 anteriorly, and 1 posteriorly). No other sternal or leg modification could be observed. Male gonopodal aperture on segment 7 wide, elliptical, about twice as wide as long, gonopods in situ usually deeply embedded, with acropodites crossing each other. Coxa ( Figs 17–18 , c) long, slender, about twice as long as wide, without apophysis but with small apophyseal macroseta (cm). Cannula normal, hidden on mesal side. Telopodite consists of two simple processes ( Figs 17–18 ) forming a simple, forceps-like appearance typical for Riukiaria ( Tanabe & Shinohara 1996) , the shorter branch being the prefemoral process (pfp), growing proximally from the base of prefemur, the latter being thick and short, and densely covered with long hairs. Prefemoral process about 3/4th of length of acropodite, devoid of any seta, knob, or additional process, flattened, parallel-sided, spatula-shaped, almost transparent. Acropodite (as a continuation of prefemur) long, scythe-shaped, arched proximally towards prefemoral process, with its slightly broadened to triangular, pointed tip (s) almost bending back to that. Distinction between prefemur and acropodite indefinite, hairs becoming scarcier at about 1/3rd of total length, but about half length still a strong macroseta (ms) on lateral side of acropodite. Prostatic groove runs straight medially along mesal side of acropodite, and ends indistinctly on its pointed tip.

Female cyphopods ( Fig. 19 ) closely packed behind 2nd legpair, in large, ∞-shaped aperture, valves (v) are oval, nearly as high as wide, densely setose, operculum (op) on lateral side small, less than half as high as valves, with fewer and shorter but stronger setae, receptacles (r) embracing valves both anteriorly and posteriorly, subrectangular, with several series of short hairs only along ventral margin.

Distribution. R. mundyi sp. n. is restricted to Yonaguni-jima Island, the southwesternmost member of the Yaeyama Island Group, southern Ryukyus, Okinawa Prefecture, Japan.

Remarks. Yonaguni-jima island, the type locality of R. mundyi sp. n., is situated about 100 km east of Taiwan, and 80 km west of Iriomote-jima, another member of the Yaeyamas. On two of this latter island group, Iriomotejima and Ishigaki-jima islands, another species, R. chelifera , occurs. It is slightly larger (body length 45 mm), and its color pattern is different: head, antennae, proterga, large part of metaterga anteriorly dark brown or grey, posterior margin, paranota, tip of epiproct, and legs yellow. This is in strong contrast with the uniformly orange-yellow color of the new species. Male gonopods also differ, acropodite and prefemoral process being straight, slender, and almost equal in length, as opposed to the longer and curved acropodite with macroseta in R. mundyi sp. n.

Comparison to the possible Taiwanese species, R. cohaesiva , R. contigua , and R. uraensis (from the region of Taipei, Wulai), all inadequately described and poorly illustrated by Wang (1956, 1957), is impossible without freshly collected material.

Specimens of the new species in Yonaguni-jima were mostly collected along the edge of natural, deciduous forests, mostly in moist litter under the large leaves of Alocasia odora , but also close to human-disturbed areas like abandoned construction sites, ruined cave entrances etc. Adult specimens were collected at the locality Kuburabari, too, which is actually a pasture for the native, endemic race of horse (the Yonaguni pony), and these specimens were distinctly smaller than members of the other populations. This is perhaps due to that relatively harsh environment, the wind-swept rocky grassland on the western side of the island, generally poor in organic litter. The species was mentioned and illustrated as an undescribed Riukiaria from Yonaguni-jima island by Tanabe (2005). It was included into the Red Data Book of threatened wildlife of Okinawa and, though categorized as ’data deficient’ (DD), its habitat was proposed for preservation. According to our observations, the species is not confined to any characteristic or undisturbed biotope on Yonaguni-jima Island so perhaps habitat conservation is not the best approach, but considering that the total area of the island itself is only 28.8 square kilometers, the populations of the new and unique species are indeed worthy of legal protection.

Figures

FIGURES 17 – 19. Riukiaria mundyi sp. n. 17 – 19 = Left gonopod of paratype male, lateral and mesal views; 19 = Left cyphopod of paratype female, posterior view. Scale 0.5 mm. ms = macroseta, other abbreviations as in Figs 1, and 10 – 13.