Riukiaria maculata, 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 : 58-62

Riukiaria maculata sp. n.

Figs 2–3 , 7–13.

Holotype male (NSMT-My 377)— Japan, Northern Ryukyus, Osumi Group, Tane-ga-shima Island, Nakatane Town, Cryptomeria mixed forest close to the airport, 260 m alt., N30.6401° E130.9797°, 7 July 2010, leg. R. & Z. Korsós.

Paratypes: 3 females, 3 juvs (NSMT-My 378, HNHM)—Same locality and date.

3 females ( RUMF)— Japan, Northern Ryukyus, Osumi Group, Tane-ga-shima Island, Nakatane Town, Cryptomeria forest close to the airport, 260 m alt., N30.6401° E130.9797°, 12 October 2009, leg. Z. Korsós & Y. Nakamura.

Diagnosis. A species 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 all congeners by its coloration (a pair of distinct dark, brownish-black patches on each segment, including collum), by its exclusive occurrence on a single island (Tane-ga-shima), and in details of gonopod morphology: a small but definite triangular process ventrally on coxa ( Figs 10-11 , tp), and by shape and length of both prefemoral process and acropodite.

Etymology. Named after the color pattern, unusual in the genus (adjective, feminin).

Description. Measurements: Medium sized species in comparison to other members of the genus. Length of holotype male 40 mm, midbody paranotal width 7.5 mm, metatergal length 1.9 mm, collum width 6.2 mm, length 2.7 mm. Adult female body length 40–43 mm, midbody paranotal width 7.7–8.5 mm, metatergal length 1.8–2.2 mm, collum width 6.4–6.7 mm, length 2.9–3 mm (n= 3).

Color in life ( Fig. 2 ): Same coloration in both sexes, prozona, metazona with yellow background, metaterga laterally with a pair of distinct, oval, brownish-black patches, occupying about 1/4th of total paranotal width on both sides. Paranota yellow with slightly darker, orange margins. Head dark greyish-brown, antennae, legs, and underside pale yellow or whitish. Collum with broad yellow anterior and lateral margins, the two dark spots closer to each other than on following metaterga. Last segment with epiproct uniformly yellow. Dark patches also distinct in UV light ( Fig. 3 ), their fluorescence much less intense. Preserved specimens (70% ethanol) after 10 months still have the typical pattern, although the patches are somewhat faded. Juvenile specimens (with body length of ca. 15 mm) uniformly greyish-yellow, and do not show the characteristic spots.

Head smooth, epicranial suture distinct, 2+2 frontal setae, 1+1 between antennal sockets, 1+1 above clypeus, and 2 dense rows at its margin and on labrum. Antennae straight, first article globose, 2nd about twice as long as first, articles 3–6 subequal in length, slightly longer than 2nd, 7th smallest, shorter than wide. Anterior part of gnathochilarial stipites and lamellae linguales densely hairy, mentum with a distinct, median hair-field.

Collum convex, smooth, shiny, lateral and posterior margins with very weak ridge, lateral corners triangular, pointed caudad. Pro- and metaterga (Fig. 7) smooth without traces of tubercles or punctuation, but from 5th onwards with definite posterior marginal ridge. Posteriolateral edge of paranota 2–3 triangular, of 4th and onwards pointed caudad. Pores on paranota 5,7,9,10,12,13,15,16,17, and 18, in median depression in lateral view. Body sides between segments 5-16 parallel, segments 17–19 strongly tapering, posteriolateral projections becoming more pointed. Epiproct in dorsal view triangular, its straight shape only broken by 3+3 lateral and 1+1 apical knobs (Fig. 8), in lateral view protruding over paraprocts (anal valves), parallel-sided, straight. Setation: 1+1 anterio-laterally on knobs, 4+4 medially on lateral sides, 2 of them on knobs, and 2+2 apically, not on knobs. Paraprocts marginate with 2+2 setae, one pair marginally, the other pair posteriorly on sides of paraprocts, hypoproct wide subtrapezoid, with 1+1 setae on knobs.

Midbody legs well separated, in male closer to each other (1.8 mm), in females separated by 2.4–2.5 mm, sterna smooth. Postgonopodal legs (in both sexes) with well-developed ventral spine on prefemur, increasingly stronger towards body end, coxa and prefemur subequal in length, femur long and slender, slightly clavate, about 2.5x as long as prefemur, postfemur and tibia subequal in length, postfemur thicker, tibia more slender, its length about 1/3rd of femur, tarsus even more slender, about 1.5x as long as tibia, claw (ca. 0.5 mm long) slightly curved.

Sexual characters: Coxa of 2nd legpair (Fig. 9) of holotype male with well-developed median projections about half as long as length of coxa, apically rounded without membraneous tubulae, with several short setae, 2+2 macrosetae sitting proximally from j oint of prefemur (1 anteriorly, 1 posteriorly), and 1+1 small ones on lateral FIGURES 7–9. Riukiaria maculata sp. n. holotype male. 7= Anterior body part, dorsal view; 8= Epiproct and 19th segment, dorsal view; 9= Sternum, coxa, and prefemur of 2nd legpair, posterior view. Scales 1 mm (7,8), 0.5 mm (9).

sides of coxa. Sternum on segment 4 (legpair 3) narrow, without lobes, on segment 5 (legpairs 4–5) and 6 (legpairs 6–7) gradually wider and smoother, bridging the 1.8 mm intercoxal distance on postgonopodal legs. No other sternal or leg modifications could be observed. Male gonopodal aperture on 7th segment wide, elliptical, about twice as wide as long, gonopods in situ usually deeply embedded, with acropodites crossing each other. Coxa ( Figs 10– 11 , c) stout, approximately as long as wide, without proximal apophysis but with small apophyseal macroseta (cm), and distally (ventrally) with small but definite, triangular projection (tp). Cannula normal, situated on mesal side. Telopodite has two simple processes ( Figs 10–12 ), a shorter, more slender prefemoral process (pfp), and a long, curved, leaflike acropodite (solenomere, s), delimitation of which from the densely setose prefemur is hardly visible. The two processes form the the simple, forceps-like gonopodal apparatus typical for Riukiaria ( Tanabe & Shinohara 1996) . Prefemoral process slender, triangular ( Fig. 12 , pfp), about 3/4th of length of acropodite, with no setae, hairs, or processes. Tip of acropodite ( Fig. 12 , s) bending backwards toward prefemoral process, almost touching it, its sides gradually tapering, prostatic groove running along mesal side, and ending on the pointed tip.

Female cyphopods ( Fig. 13 ) embedded closely behind 2nd legpair, in large, ∞-shaped aperture, valves (v) subrectangular, almost twice as wide as high, densely setose, with basal bumps of each seta giving a rough appearance to its surface and margins. Lateral operculum (op) large, thick, almost as high as valves, with dense setation, receptacles (r) embracing valves both anteriorly and posteriorly, subrectangular, with several series of short hairs along ventral, serrated-like margin.

Distribution. Known only from Tane-ga-shima Island, northern Ryukyus (Osumi Island Group), Kagoshima Prefecture, Japan. Specimens were found in the single locality of a mixed forest of deciduous trees, possibly an old Cryptomeria japonica plantation. Search in other similar habitats on the island (about 445 square kilometers of total surface area) produced no more specimens.

Remarks. Tane-ga-shima island, the locality of the new species’ population, is a member of the Osumi Islands, Northern Ryukyus, about 50 km southeast of Kyushu. It is an elongate island 57 km from north to south, and about 5–12 km from east to west, with the highest elevation 282 m. The nearest island is the small, uninhabited Mage-jima, with an area of only 8 km 2, and with no worth-while habitat for native millipedes. Yaku-shima island, on the other hand, the largest member of the Osumi Group, is about 30 km to the west, and has a notable vegetation and fauna. Its high mountains (up to 1936 m a.s.l.) are mainly covered by ancient Japanese cedar ( Cryptomeria japonica ) forest, and provide an optimal habitat for many endemics. Two Riukiaria species have been described from Yaku-shima ( R. puella and R. jamila ), but they both differ considerably in size (32–36 mm) and coloration from R. maculata sp. n.: R. puella is almost entirely yellow, whereas tergites of R. jamila are gray with yellowish white paranota. (For gonopod differences see Diagnosis.)

In the southern part of Kyushu, one of the four main islands of Japan, three Riukiaria species are known to occur: R. cornuta , R. anachoreta , and R. semicircularis . Whereas their size is similar ( R. anachoreta , body length 39–45 mm, R. semicircularis 40 mm) to, or larger ( R. cornuta , 55 mm) than R. maculata sp. n., all three have a generally greenish or brownish gray color, with a little yellow or whitish tint on the paranota in R. cornuta and R. semicircularis . Moreover, metatergites of R. anachoreta show 3 transverse rows of conspicuous tubercles. Male gonopods also differ in the length and shape of the acropodite and prefemoral process, the former in case of R. cornuta bearing a small mesal tooth. The prefemoral process of R. semicircularis is long and slender, undulated like a flagellum, and only a little shorter than the acropodite, the tip of which bends backwards to form an almost completely closed oval.

Based only on superficially similar coloration, we also might to compare R. maculata sp. n. with R. falcifera from Okinawa-jima island. The two locations are more than 500 km apart by sea, and R. falcifera is considerably larger (53–65 mm), but its coloration also differs from the new species, the dark spots never being so strong, and not of the same size. In R. maculata , the spots are always widely separated by the yellow median part, and all are the same size on each segment, giving really a 'spotted' appearance to the animal. In R. falcifera , on the other hand, the spots are blurred, sometimes missing or fused together, and change in their size and shape along the body of the animal.

Since R. maculata sp. n. is only known from a single population, and because its attractive, colorful appearance we recommend the new species for full legal protection. The new species could well be one of the rarest Riukiaria species in Japan.

Figures

FIGURES 2 – 3. Riukiaria maculata sp. n., holotype male. 2 = Live coloration, Tane-ga-shima; 3 = Live specimen in UV-light. FIGURES 4 – 6. Riukiaria mundyi sp. n., paratype specimens. 4 = Live coloration, Yonaguni-jima; 5 – 6 = The same specimens in ambient flashlight, and in UV-light.

FIGURES 10 – 13. Riukiaria maculata sp. n. 10 – 12 = Left gonopod of holotype male, lateral, mesal, and apical (ventral) views, respectively; 13 = Left cyphopod of paratype female, posterior view. Scales 0.5 mm. c = coxa, tp = triangular process, v = valve, r = receptacle, op = operculum, other abbreviations as in Fig. 1.