Pleuronichthys cornutus ( Temminck & Schlegel, 1846 )

Yokogawa, Kōji, Watanabe, Ken-Ichi & Ogihara, Gota, 2016, Redescriptions of two closely related East Asian flatfish species of the genus Pleuronichthys, Zootaxa 4205 (1), pp. 1-23 : 14-16

Pleuronichthys cornutus ( Temminck & Schlegel, 1846)

(New English name: Phantom frog flounder)

( Figs. 3 D–F, 4C, D, 5F–J; Tables 1–5)

Platessa cornuta: Temminck & Schlegel, 1846: 179 –180, pl. 92(fig. 1), syntypes (type locality: Japan) ; Boeseman, 1947: 145 – 146, RMNH 1334, 1335 , 1336, 3496c and 3496d (synonymy; Japan) .

Pleuronichthys cornutus : Jordan & Starks, 1906 (part): 201–202 [synonymy and description; Japan (Kobe, Aomori, Hiroshima, Nagasaki, Hakodate , Onomichi , Wakanoura , Tsuruga , Tokyo and Misaki )]; Oshima , 1927: 194 –196 [synonymy and description; Formosa ( Taihoku )]; Wu , 1932 (part): 109–110 [synonymy and description; China ( Ting-Hai , Techou-San , Tchefou , Tsing-Tao , Pekin and Amoy )]; Fowler , 1933: 169 –170, fig. 8 [synonymy, brief description and illustration; China ( Hong Kong)]; Tanaka & Abe , 1955: 223 (brief description and illustration; Japan); Zheng , 1955 (part): 286–287, fig. 177 [synonymy, description and illustration; China ( Zhuanghe , Pikou , Qinhuangdao , Longkou , Yantai , Shidao , Qingdao and Shijiusuo )]; Li & Zhang , 1991 (part): 78–79, fig. 87 [brief description and illustration; China ( Bohai Sea )]; Tchang et al., 1994 (part): 286–287, fig. 177 [synonymy, description and illustration; China ( Zhuanghe , Pikou , Qinhuangdao , Longkou , Yantai , Shidao , Qingdao and Shijiusuo )]; Li & Wang , 1995 (part): 238–241, fig. II-62-1 [synonymy, description and illustration; China ( Dalian , Qingdao , Shenjiamen , Xiamen )]; Kitagawa et al., 2008: 113 [color photos; Japan ( Tohoku district )]; Minemizu & Mastuzawa , 2010: 290 –291 [(color photo; Japan ( Ose Cape )]; Yokogawa et al., 2014: 385 –392, fig. 1 (photo of the lectotype); Yokogawa, 2015; Yokogawa, 2016.

Pleuronichthys cornutus , MDH-B type: Kato & Fujio, 1979: 10 –12, fig. 2(lower photo) [monochrome photo; Japan ( Sendai Bay , off Fukushima and Ibaraki Prefs.)].

Pleuronichthys cornutus, Bakemeita type: Nozawa & Kato, 1981: 1 –8, fig. 1(lower photo) [monochrome photo; Japan (off Tottori Pref.)]; Matsuoka et al., 1989: 23 –36, fig. 1(B) (color photo; East China and Yellow Seas); Watanabe et al., 1992: 2253 –2260 [ Japan ( Kii Channel )]; Watanabe , 1994: 1–73, fig. 1-5 [illustration of juvenile; Japan (waters around Tokushima)]; Watanabe et al., 1994: 515–520 [ Japan ( Kii Channel )]; Watanabe et al., 1996a: 17 –22 [ Japan ( Kii Channel )]; Watanabe et al., 1996b: 23 –27 [ Japan ( Kii Channel )]; Matsuoka , 1996a: 47 –54 ( East China and Yellow Seas); Matsuoka , 1996b: 55 –62 ( East China and Yellow Seas).

Pleuronichthys cornutus , WK-B type: Watanabe & Numachi, 1988: 765 –772 [ Japan (Kii Channel)].

Pleuronichthys sp. : Yamada, 1986: 378 –379 (brief description, color photo and pictorial key; East China Sea ); Minami, 1988b: 939 –940 (description and illustration of larvae and juveniles; East China and Japan Seas, northern coast of Kyushu, San-in and Wakasa Bay); Sakamoto & Nakabo, 1988b: 458, pl. 378(A) (brief description and color photo; Japan) ; Masuda & Kobayashi, 1994: 405 figs. 3, 4 [color photos; Japan (Izu Pen.); Yamada et al., 1995: 50, 206 (pictorial key and color photo; East China and Yellow Seas); Sakamoto & Tagawa, 1997: 676 –677 [color photo; Japan (off San-in)]; Yamada & Kudo, 1998: 7 –8, 11, fig. 4(10) [monochrome photo; Japan (around Miura Pen.)]; National Fisheries Research and Development Institute ( NFRDI), 1999: 184, 456, fig. 515 (description and color photo; Taiwan, East China Sea, southern Japan and Korea) ; Wang et al., 1999: 604 –610 ( East China Sea ); Nakabo, 2000: 1372 (pictorial key, Japan) ; Sato, 2001: 265 [color photo; Japan (Iburi)]; Youn, 2002: 438, 686 (pictorial key, Korea); Kim I. et al., 2005: 483 (brief description and illustration; Korea) ; NFRDI, 2006: 337, fig. 559 (description and color photo; Taiwan, East China Sea , southern Japan and Korea) ; Yamada et al., 2007: 1041 –1047, pl. 46(7) (pictorial key and color photo; East China Sea ); NFRDI, 2008: 350, fig. 586 [description and color photo; northwestern Pacific ( Korea , southern Japan, East China Sea and Taiwan)].

Pleuronichthys japonicus: Suzuki et al., 2009: 276 –291, fig. 1(a–c) (synonymy; original description and monochrome photos; all around Japan); Ishikawa & Senou, 2010: 331 [color photo; Japan (off Miura Pen.)]; Yokogawa & Watanabe, 2011: 24 – 32, fig. 1(d) [monochrome photo; Japan (Kii Channel)]; Zhang et al., 2011a: 51 –54, fig. 1 [monochrome photo; China (around Zhoushan)]; Arao & Tamai, 2011: 23 –24, fig. 2(I) [monochrome photo; Japan (Enshu-nada)]; Ohashi & Motomura, 2011: 99 –100, fig. 29 [synonymy, brief description and color photos; Japan (northern Kagoshima Pref.)]; Zhang et al., 2011b: 967 –972, fig. 1(lower photo) (color photo; East China Sea); Igarashi & Ito, 2013: 9 –14 [Japan (off Fukushima Pref.)]; Ito, 2013: 15–22 [Japan (off Fukushima Pref.)]; Nakabo & Doiuchi, 2013: 1676 (pictorial key; Japan): Minami, 2014b: 1462 –1463 (description and illustration of larvae and juveniles; East China and Japan Seas, Seto Inland Sea, northern coast of Kyushu, San-in and Wakasa Bay).

Diagnosis. Scale length (from trunk area) greater than 1.33% of SL (Table 1), whole scale outline oval ( Fig. 3 D–F), exposed margin rounded. Scales highly deciduous, longitudinal rows occasionally irregular ( Fig. 4 C, D). Upper eye area usually greater than that of lower eye, area ratio 0.93–1.44 (Table 1). Central longitudinal scales 75–87, scales below lateral line 47–57, abdominal vertebrae 12–13 (mostly 12) (Tables 1, 2).

Description. Measurement data for length-measured characters subject to isometric growth and meristic counts are shown in Tables 4 and 5, respectively. Body rather compressed, ocular and blind sides convex and almost flat, respectively. Body elongated in smaller individuals, depth increasing and body becoming ovate with growth.

Entire body covered with small cycloid scales. Vertical scale rows essentially regular, longitudinal rows occasionally irregular ( Fig. 4 C, D). Scales more or less oval ( Fig. 3 D–F), exposed margin rounded ( Fig. 4 C, D).

Scales entirely covered by very thin, easily damaged pigmented epithelial membrane, highly deciduous. Minute scales covering entire membrane of dorsal, anal and caudal fins (both sides). Ocular and blind side pectoral fin bases covered broadly and narrowly with minute scales, respectively. Scales absent on pelvic fins.

Eyes on right side of head, globular and extremely protuberant. Upper eye usually scarcely posterior to and of greater mass than lower eye. Eye diameters proportional to HL relatively large, stable with growth, proportional to SL decreasing considerably with growth. Inter-orbital space very narrow, forming a sharp bony ridge terminating with strong conical spiny prominences on each edge, directed forward and backward, respectively. Snout very short, rounded. Two closely placed nostrils on each side, anterior nostril larger, with fleshly flaps anteriorly and posteriorly. Ocular side nostrils located on anterior extension of inter-orbital ridge, blind side nostrils on higher level than ocular side. Mouth very small, oblique, lips fleshy, lower jaw slightly projecting. Jaw lengths proportional to HL stable with growth, proportional to SL decreasing considerably with growth. Small acute conical teeth in two or three rows on blind side of both jaws, teeth in villiform bands on ocular side of both jaws. Gill rakers less developed, a few small tubercles on upper and lower limbs of first arch, counts tending to increase with growth.

Dorsal and anal fin base very long. Dorsal fin anteriorly twisted toward blind side, originating from middle of upper eye position on blind side and terminating on upper middle ridge of caudal peduncle. Anal fin originating from just posterior to vent, terminating on lower middle ridge of caudal peduncle. Caudal fin fan-shaped with rounded or rhombic edge. Pectoral fins long and slender, ocular side fin longer than that on blind side, located almost level with uppermost positions of gill slits on both sides. Pelvic fins small, blind side fin positioned slightly more anterior to ocular side fin. Dorsal, anal and pelvic fins (both sides) proportional to SL decreasing with growth, those of caudal and pectoral fins (both sides) stable.

Two lateral lines on each side. Lateral line scales developed but usually embedded subcutaneously. Main lateral line running across center of trunk to caudal base, curving gently upward before middle of trunk. Supratemporal lateral line (SLL) running along dorsal fin base, reaching middle of trunk (occasionally extending more posteriorly), curving downward sharply at supratemporal region (both sides, but often indistinct, particularly on ocular side), often a short antrorse branch from curve, running forward along supratemporal edge (Table 3).

Coloration. Ocular side fresh base coloration light to dark brown, fine or minute indistinct dark dots thinly scattered over entire side ( Fig. 5 F–I). Sometimes additional densely distributed highly contrasting, slightly overlapping large dark-brown blotches ( Fig. 5 G, H, I), occasionally dots and blotches largely absent ( Fig. 5 J). Ocular side dorsal, anal and pelvic fins with similar dots proximally, caudal membrane usually dark, pectoral fin usually with a broad dark band distally. Edges of dorsal, caudal and anal fins white in some individuals ( Fig. 5 H). Blind side uniformly white to ivory, dorsal, caudal and anal fins dusky distally, pectoral and pelvic fins white. Preserved specimens (formalin or alcohol) with ocular side base color brownish, with darkish dots and blotches; blind side yellowish.

Distribution and habitat. Pleuronichthys cornutus is broadly distributed in offshore waters around the Japanese archipelago (southward from southern Hokkaido), Korea, China (e.g., Zhoushan and Hong Kong) and Taiwan (Taipei), and also occurs in offshore waters of the southern East China Sea. The species inhabits mainly muddy bottoms in offshore deeper (from ca. 40m) waters, occurring in lower densities than P. lighti in shallower coastal waters, including the Seto Inland Sea. Possibly due to its highly deciduous scales, P. cornutus may avoid sandy bottoms. Although the species has been recorded from the western Seto Inland Sea ( Suzuki et al. 2009), such may have been a rare case as it has not been recorded from the eastern Seto Inland Sea [excluding the Kii Channel, where it is particularly abundant deeper than 100m (Watanabe, 1994)].

Remarks. Pleuronichthys cornutus was originally described by Temminck & Schlegel (1846) as Platessa cornuta , based on 8 syntype specimens, which in fact comprised two distinct cryptic species. Subsequently, Boeseman (1947) designated RMNH 1336 as lectotype . A recent revision of East Asian Pleuronichthys species by Suzuki et al. (2009) identified one species as " P. cornutus " and a second ( P. japonicus ) as new. However, Yokogawa et al.'s (2014) squamatological examination of the P. cornutus lectotype revealed that Suzuki et al.'s (2009) P. cornutus lectotype identification had been incorrect, the specimen actually being conspecific with P. japonicus . Accordingly, P. japonicus is regarded as a junior synonym of P. cornutus .

Although publications of the National Fisheries Research and Development Institute (1999, 2006, 2008) described both ocular and blind side scales of this species (as Pleuronichthys sp. ) as ctenoid, they are in fact cycloid ( Fig. 3 D–F). Blind side coloration of the caudal peduncle, observed in KAUM–I. 29267, indicated the occasional existence of ambicoloration, seen also in Pleuronichthys lighti (see above). Photographed Japanese specimens included in Kitagawa et al. (2008) and Minemizu & Mastuzawa (2010) are both considered to be P. cornutus as understood here, due to conforming body color patterns ( Fig. 5 H) and squamation.

Specimens described from Taihoku (Taipei) ( Oshima, 1927) and Hong Kong ( Fowler, 1933) are also regarded herein as P. cornutus since both descriptions noted lateral line scale (LLS) counts as 80, thereby falling within the range for this species ( Table 5 ). Similarly, Tanaka & Abe (1955) gave scale counts for a single longitudinal scale row as 80, suggesting that their material comprised or included this species. Although Jordan & Starks (1906) also noted a LLS count of 80 for numerous specimens from many localities around Japan, their description may have been based on selected specimens, including P. cornutus , because they failed to give a range for that meristic. Since their collection localities included regions around the Seto Inland Sea (Kobe, Hiroshima and Onomichi), it is likely that their material comprised both species.

Similarly, the LLS count ranges in some " P. cornutus " descriptions were most likely based upon both species, i.e., 80–103 ( Wu, 1932), 90–109 ( Zheng, 1955), 90–110 ( Li & Zhang, 1991), 90–109 ( Tchang et al., 1994) and 89– 100 ( Li & Wang, 1995). On the other hand, although Sakamoto & Nakabo's (1988b) description of Pleuronichthys sp. , is apparently consistent with P. cornutus , based upon the photograph, the LLS count range of 107–112 is problematic.

Although the records of this species (as P. sp.) from Tosa and Tateyama Bays, and the Sagami Sea, by Shinohara et al. (2001), Hagiwara & Kimura (2005) and Shinohara & Williams (2006), respectively, were presently unidentifiable, they can be identified when examining registered museum specimens. While the records of P. sp. and P. japonicus , respectively, Aomori Pref., Japan by Shiogaki et al. (2004) and Yamanaka & Ito (2014) may be problematic as they did not include references to voucher specimens.

Because the flesh of P. cornutus is soft, the quality declining quickly after death, the species has a low market value, unlike P. lighti , in spite of their very similar appearance ( Yamada, 1986; Sakamoto & Nakabo, 1988b; Yamada et al., 2007). This feature may be reflected in the lectotype (RMNH 1336, see Yokogawa et al., 2014, fig. 1) and some paralectotypes (RMNH 1334 and 1335) of P. cornutus (stuffed specimens), due to their wrinkled skin, suggesting that the bodies had already softened considerably by the time they were stuffed.

Figures

FIGURE 3. Scales of Pleuronichthys lighti (A – C) and P. cornutus (D – F). A, D: ocular side, trunk, area above lateral line; B, E: ocular side, trunk, area below lateral line; C, F: blind side, trunk, area above lateral line. Bars indicate 0.2 mm. Photographs selectively cited from Yokogawa & Watanabe (2011).

FIGURE 4. Trunk squamation (ocular side) of Pleuronichthys lighti (A, B) and P. cornutus (C, D). A: BSKU 37610; B: SNFR 13740; C: SNFR 1428; D: SNFR 15497 - 2.

FIGURE 5. Ocular side coloration variations in fresh Pleuronichthys lighti (A – E) and P. cornutus (F – J). A: BSKU 114101; B: BSKU 118425; C: BSKU 118426 (A – C were photographed by K. Yokogawa); D: KAUM – I. 20492; E: KAUM – I. 5064; F, G: Uncatalogued specimens (F and G were photographed by K. Watanabe); H: KAUM – I. 30446; I: KAUM – I. 29267; J: KAUM – I. 4229 (KAUM specimens were photographed by the Kagoshima University Museum).