Platyrhina hyugaensis Iwatsuki, Miyamoto and Nakaya

Iwatsuki, Yukio, Miyamoto, Kei, Nakaya, Kazuhiro & Zhang, Jie, 2011, A review of the genus Platyrhina (Chondrichthys: Platyrhinidae) from the northwestern Pacific, with descriptions of two new species, Zootaxa 2738, pp. 26-40 : 30-34

Platyrhina hyugaensis Iwatsuki, Miyamoto and Nakaya sp. nov.

New English name: Hyuga Fanray

New Japanese name: Onino-uchiwa

Figs. 2 A–B, 3A–C, 4, 5; Table 1

Holotype. MUFS 21609, male, 391 mm TL, Meitsu, Miyazaki, Japan (31°31’59”N, 131°22’55”E), set net, coll. Y. Iwatsuki, 10 Oct. 2001.

Paratypes (161−431 mm TL, n =10). FRLM 1711, 378 mm TL, female, mouth of Ago Bay, Shima, Mie, Japan, set net; FRLM 29894, female, 359 mm TL, mouth of Ago Bay, Shima, Mie, Japan, set net; MUFS 3551– 3552, 2 specimens, males, 202–279 mm TL, off Aoshima, Miyazaki, Japan, shallow trawls, coll. M. Akazaki, 23 June 1975; MUFS 3553, female, 210 mm TL, same data as MUFS 3351–3352; MUFS 5555, female, 189 mm TL, off Aoshima, Miyazaki, Japan, shallow trawls, coll. M. Akazaki, 17 Mar. 1975; MUFS 7272, female, 161 mm TL, off Aoshima, Miyazaki, shallow trawls, coll. M. Akazaki, 30 Sep. 1976; MUFS 23164, female, 431 mm TL, Meitsu, Nango-cho, Miyazaki, Japan, set net, coll. K. Miyamoto, 27 June 2007; MUFS 23225, female, 335 mm TL, Uchinoura Bay, Uchinoura-cho, Shibushi Bay, Kagoshima, Japan, coll. K. Miyamoto and Y. Iwatsuki, 6 Aug. 2007; MUFS 26936, female, 423 mm TL, set net, coll. H. Izumi, Iorigawa, Kadokawa Bay, Miyazaki, Japan, 13 Nov. 2008.

Diagnosis. Distinguished from congeners in having the following combination of characters: one row of thorns (strongly hooked) on mid-dorsum of tail; a pair of thorns on anterior part of scapular region (apparent to touch in smallest specimen; 161 mm TL) ( Fig. 3 B, indicated by white arrows); thorns on orbital, nape and scapular regions not encircled by light yellow or white pigment ( Figs. 2 A–B, 3A–C); dorsal surface covered with minute dermal denticles of uniform size and shape, no obvious larger dermal denticles (smooth to touch).

Description. Counts and proportional measurements of the holotype and 10 paratype specimens of Platyrhina hyugaensis sp. nov. are shown in Table 1. Data for the holotype are presented first, followed by those of other specimens in parentheses.

Disk broadly wedge-shaped, snout tip slightly angular, outer margins broadly rounded, free rear tip reaching or slightly beyond level of cloaca; preorbital and preoral snout lengths, 10% (10–14%) of TL and 10% (10–13%) of TL, respectively (Fig. 4); pelvic fins rounded (free rear tips angled), originating from abdominal surface at end of pectoral fins; tail shark-like, length greater than disc length, 64% (53–64%) of TL, abruptly narrower than disc width, lacking a caudal spine, abdominal surface flat with shallow groove along mid-abdominal axis; one row of thorns (strongly hooked) on mid-dorsum of nape to second dorsal fin origin; dermal-lateral folds on tail, originating well anterior to free rear tip of pelvic fin, reaching just behind caudal fin origin; two widely separated dorsal fins on tail, similar in size and shape, moderately large, anterior margins slightly convex with convex hind margin; first dorsal fin originating 1.4 (1.2–1.4) times maximum disc width from snout tip, well behind free rear tips of pelvic fins but anterior to mid-length of tail; second dorsal fin originating 1.6 (1.4–1.6) times maximum disc width from snout tip; interdorsal space 1.4 (1.4–2.0) times first dorsal fin base length, 1 (1–2) thorns on mid-dorsum; caudal fin relatively small, flat, oval, sometimes forming small lobe posterodorsally, dorsal margin length equal to (0.9–1.0 times) abdominal margin length; head moderately elongate; snout moderately long, soft, flexible; eyes moderately large, not elevated or protruding; spiracles leaf-shaped, 1.1 (1.0–1.6) times eye length, originating beside eyes; nostrils moderately large, nasal flap skirt-shaped; anterior aperture circular, lower part surrounded by short folds; mouth width moderate, upper and lower jaws arched, skin grooves around mouth; oral teeth small, rhomboid, slightly pointed in males, over 71 (57–67) regular rows on lower jaw (increasing with growth), upper and lower jaw teeth similar in shape and size; five pairs of gill openings, two anteriormost widely separated, distance between second to fifth gradually becoming narrower posteriorly; 6 (3–6) thorns around on orbits; two pairs of two (total eight, Fig. 3 B) symmetrical thorns on scapular region; a pair of thorns on anterior part of scapular region (apparent to touch in smallest specimen, 161 mm TL) ( Fig. 3 B, indicated by white arrows); thorns on orbital, nape and scapular regions not encircled by light yellow or white pigment ( Figs. 2 A–B, 3A–C); claspers of mature males greatly elongated; entire body and fins covered with minute dermal denticles of uniform size and shape, no obvious larger dermal denticles on dorsal surface (smooth to touch); somewhat irregular small thorns aggregated on anterodorsal margin of disk from snout tip to maximum disc width.

Color of fresh specimens. Based on holotype ( MUFS 21609) and 3 paratypes ( MUFS 23164, 23225 and 26936) photographed by K. Miyamoto and Y. Iwatsuki: dorsal surface often grayish-brown, darker medially; dorsal and caudal fins brown; abdominal surface whitish, outer margins of pectoral and ventral fins broadly grayishbrown.

Color of preserved specimens. Dorsal surface often grayish-brown, darker medially; dorsal and caudal fins somewhat yellowish-brown; abdominal surface whitish, outer margins of pectoral and ventral fins broadly grayishbrown.

Distribution. Platyrhina hyugaensis sp. nov. is currently known only from southeastern Kagoshima (Uchinoura Bay), Miyazaki (Hyuga Nada Sea) and Mie (Shima) Prefectures, Southern Japan, all facing the Pacific Ocean ( Fig. 5 ). According to S. Kimura (personal communication), extensive observations off Mie Prefecture have resulted in several limited specimens being over ca. 30 year period, although the species has been commonly observed off Miyazaki, in the Hyuga Nada Sea. The apparent absence of the species from waters surrounding the Ogasawara and Ryukyu Islands suggest a very limited distribution. Additional examples of P. hyugaensis have not been found in any museum collections or during field sampling throughout the western Pacific region. The species is therefore considered to be endemic to the waters off southeastern Japan.

A similar distributional pattern can be seen in other shallow coastal Japanese species, such as the gerreids Gerres microphthalmus and G. akazakii , centropomid Lates japonicus and myriopristid Myripristis kochiensis (see Iwatsuki et al. 2002, 2007; Katayama & Taki 1984; Randall & Yamakawa 1996). This may be related to sea water temperature ( Iwatsuki et al. 1993, 2002, 2007; Randall & Yamakawa 1996), the area of distribution being closely related to a mean minimum winter sea surface temperature of 16 ºC (persistent for last ca. 100 years) ( Kuniji et al., 1985). Such may be a limiting factor for survival in winter. Furthermore, the presence of all life history stages indicates that such species spawn and grow within this region. Accordingly, we recognize these species and P. h y u - gaensis, as endemic to the above noted area, Hyuga Nada Sea.

Ecological notes. Specimens of Platyrhina hyugaensis sp. nov. have been frequently captured by set net within a depth of ca. 50 m from early spring (March) to autumn (November), whereas P. tangi sp. nov. has been commonly observed throughout the year. According to a local fisherman and a fish merchant (M. Wada and H. Kadokawa, respectively; personal communication), examples of the formers were not included in almost daily setnet catches (depth ca. 8–50 m) from November to March in 2007–2008 in northern Miyazaki (Kadokawa Bay, 32°47’79”N, 131°66’29”E) and southern Miyazaki (Meitsu, Nichinan Coast, 31°54’27”N, 131°38’56”E), respectively. This indicates that the species avoids lower sea temperatures in the winter season. At the same time, P. tangi were commonly captured, indicating significantly differing histories in the Hyuga Nada Sea.

The stiff and robust nature of the claspers of two male specimens (MUFS 3351, 279 mm TL and MUFS 3352, 202 mm TL) of P. hyugaensis indicated recent attainment of maturity (personal observation; A. Yamaguchi, personal communication). Platyrhina tangi , on the other hand, reaches sexual maturity at a greater size, 50% of specimens (393 mm TL, males and 421 mm TL, females) being sexually mature ( Yamaguchi & Kume 2009).

FIGURE 4. Relationships of preorbital snout length (A) and preoral snout length (B) to total length in Platyrhina : P. s i n e n s i s, P. tangi sp. nov. and P. hyugaensis sp. nov., male and female respectably. Regression equations of (A), S: P. s i n e n s i s (male and female), y=0.155x–0.765, R2=0.97; T: P. tangi (male and female), y=0.125x+1.253, R2=0.98; H: P. hyugaensis (male and female), y=0.089x+7.264, R2=0.97; all P<0.0001. Regression equations of (B), S: P. s i n e n s i s (male and female), y=0.151x+4.753, R2=0.97; T: P. tangi (male and female), y=0.130x+0.901, R2=0.98; H: P. hyugaensis (male and female), y=0.099x+4.691, R2=0.98; all P<0.0001.

Etymology. The specific name, “ hyugaensis ”, is proposed for this species, reflecting our belief that it is endemic and common to the Hyuga Nada Sea.

Remarks. According to local divers in Miyazaki, Platyrhina hyugaensis sp. nov. often occurs on very shallow sandy bottoms, in depths as shallow as ca. 1 m, in the summer season off the Nichinan Coast, Miyazaki, whereas P. tangi sp. nov. is usually deeper in (discernible by yellow spots on the dorsal surfice easily) ca. 10– 30 m.

Figures

FIGURE 2. Three species of Platyrhina and close up of tail for each species. A – C) Platyrhina sinensis, D – F) P. hyugaensis sp. nov. and G – I) P. tangi sp. nov. A) ASIZB 182251, male, 350 mm TL, off Amoy, China; B) ASIZB 182256, female, 455 mm TL, off Amoy, China; C) Same specimen of (A), close up of tail; D) MUFS 21609 (holotype), male, 391 mm TL, Meitsu, Miyazaki, Japan; E) MUFS 23164 (paratype), female, 431 mm TL, Meitsu, Miyazaki, Japan; F) Same specimen of (D), close up of tail; G) MUFS 23163 (holotype), male, 398 mm TL, Meitsu, Miyazaki, Japan; H) KPM-NI 2488 (paratype), female, 434 mm TL, Mera, Shizuoka, Japan; I) Same specimen of (G), close up of tail.

FIGURE 3. Differences between A – C) Platyrhina hyugaensis sp. nov. and D – F) P. t a n g i sp. nov.; A – C) MUFS 23164 (holotype), female, 431 mm TL, Meitsu, Miyazaki, Japan; D – F) KPM-NI 2488 (paratype), female, 434 mm TL, Mera, Shizuoka, Japan. White and black arrows show a pair of thorns on the anterior part of scapular region and subsequent irregular small thorns on two pairs of two (total eight) symmetrical thorns, respectively.

FIGURE 5. Distribution of Platyrhina sinensis, P. hyugaensis sp. nov. and P. t a n g i sp. nov. Black dots based on specimens examined during this study; white dots based on literature records (as P. s i n e n s i s).