Pleuronichthys lighti Wu, 1929

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 : 4-13

Pleuronichthys lighti Wu, 1929

(New English name: Common frog flounder) ( Figs. 3 A–C, 4A, B, 5A–E; Tables 1–5)

Platessa cornuta (not of Temminck & Schlegel): Boeseman, 1947: 145 –146, RMNH 3496 a, 3496b, 3501 (synonymy; Japan).

Parophrys cornuta (not of Temminck & Schlegel): Günther, 1862: 455 (synonymy and description; Japan); Günther, 1880: 70 [synonymy; Japan (Kobe)]; Nyström, 1887: 42 –43 (synonymy; Japan); Otaki, 1897: 32 –33, pl. 8 (synonymy, brief description and illustration; Japan).

Pleuronichthys cornutus (not of Temminck & Schlegel): Steindachner, 1896: 217 [synonymy and description; Japan (Kobe or Nagasaki)] ; Jordan & Snyder, 1900: 379 [list; Japan (Hakodate and Tokyo Bay)] ; Jordan & Snyder, 1901: 769 [list; Japan (Yokohama)]; Jordan & Starks, 1906 (part): 201–202 [synonymy and description; Japan (Kobe, Aomori, Hiroshima, Nagasaki, Hakodate, Onomichi, Wakanoura, Tsuruga, Tokyo and Misaki)]; Starks & Thompson, 1910: 279 –282 [description; Japan (Tsuruga and Aomori)]; Snyder 1912: 440 [ Japan (Hakodate, Tokyo and Tsuruga)] ; Jordan & Thompson, 1914: 309 [ Japan (Osaka and Misaki)]; Hubbs, 1915: 475 –476 [synonymy and description; Japan (waters near Kagoshima, Goto Is., Genkai Sea and Tsuruga)]; Matsuura & Izuka, 1920: 117 [list; Japan (Takamatsu)] ; Jordan & Hubbs, 1925: 298 [ Japan (Tokyo, Kobe, Toba, Kagoshima, Mikawa Bay, Misaki and Fukui)]; Wu, 1932 (part): 109–110 [synonymy and description; China (Ting-Hai, Techou-San, Tchefou, Tsing-Tao, Pekin and Amoy)]; Wang, 1933: 52 –53 [synonymy and description; China (Chefoo)]; Norman, 1934: 319 –320, fig. 236 (synonymy, description and illustration; Japan (Kobe, Bay of Mutsu , Tokyo, Matsuyama, Hiroshima, Wakanoura and Inland Sea) , China (Yenting and Amoy)]; Okada et al., 1935: 239, pl. 141 (description and monochrome photo; Japan); Kamohara, 1952: 82, fig. 79 [illustration; Japan (off Kochi City)]; Chyung, 1954: 473 –474 (synonymy and description; Korea) ; 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)]; Okada, 1955: 384 –385 (description; Japan); Tomiyama et al., 1958: 40 (brief description and illustration; Japan); Hiyama & Yasuda, 1961: 124, pl. 169(291) (brief description and illustration; Japan); Zheng, 1962: 981 –982, fig. 763 [synonymy, brief description and illustration; China (Haimen, Jiazi, Zhelang, Shanwei and Jieshi)]; Tchang & Wang, 1963: 527 –528, fig. 394 [synonymy, brief description and illustration; China (Shenjiamen, Kanmen, Dachen Is., Sijiao and Suao)]; Fitch, 1963: 18 –20, fig. 3 (monochrome photo, synonymy and description; China, Japan and Korea); Chen & Weng, 1965: 8 –9: [synonymy, description and illustration; Taiwan (Kaohsing, Pescadores Is., Taichung and Keelung]; Ochiai, 1965: 492 (brief description and illustration; Japan) ; Shen, 1967: 191 –192, figs. 77–80 (synonymy, description and monochrome photos; Hong Kong); Hiyama & Yasuda, 1971: 303, fig. 405 (brief description and illustration; Japan); Burgess & Axelrod, 1974: 1097 [color photo; Taiwan (Pescadore Is.)]; Masuda et al., 1975: 345, pl. 148(I) (color photo; Japan); Chyung, 1977: 569, pl. 301, color pl. 126-1 [brief description, monochrome and color photos; Korea (Pusan and Yeosu)]; Shirano, 1979: 108 [(illustrations; Japan (Kagoshima)]; Fisheries College of Shanghai et al., 1980: 146 –147, fig. 113 [brief description and illustration; China (Fujian Prov.)]; Kataoka & Tomida, 1981: 76, [list; Japan (various sites around Mie Pref.)]; Shen, 1982: 199 –201, fig. 2 [description and monochrome photo; Taiwan (Ta-chi, Tungkong and Su-au)]; Masaki & Ito, 1984: 11 –51 [ Japan ( western Seto Inland Sea )]; Shen, 1984a: 137, pl. 137(440-1a, b) (brief description and color photos; north-eastern waters of Taiwan) ; Shen, 1984b: 451 –452 (key and illustration; Taiwan) ; Chen & Yu, 1984: 821 –823, fig. 6-173(2) (key and illustration; Taiwan) ; Sakamoto & Nakabo, 1984: 337, 352, pl. 315(G) (brief description and color photo; Japan); Matsuura, 1985: 620 –621, fig. 393 [description and color photo; Japan (Okinawa Trough)]; Kamohara & Okamura, 1985: 60, pl. 131(652) (illustration; Japan) ; Miao, 1985: 539, fig. 738 [synonymy, brief description and illustration; China (Shacheng, Taishan, Dongxiang, Xiamen, Sangou and Waixie fishing grounds)]; Mochizuki, 1985: 126 –127 [color photo; Japan (Awaji I.)]; Yamada, 1986: 380 –381 (brief description and color photo; East China and Yellow Seas); Ochiai, 1986: 313 (brief description and color photo; Japan) ; Masuda & Allen, 1987: 464 (color photo; Japan); Cheng & Zheng, 1987: 500 –502, 1404, fig. 2574 (key and illustration; China); Chen, 1987: 428 –429, fig. 290 [brief description and illustration; China (northern Yellow Sea and Liaodong Bay )]; Abe, 1987: 925 (brief description and illustration; Japan) ; Minami, 1988a: 938 –940 [description and illustration of larvae and juveniles; Japan (Seto Inland Sea, coastal waters of Honshu, Kyushu and Hokkaido), southern Korean Peninsula and Yellow Sea]; Sakamoto & Nakabo, 1988a: 337, 352, pl. 315(G) (brief description and color photo; Japan) ; Xu, 1990: 361, fig. 229 [brief description and illustration; China ( Yangtze River estuary)]; Shao & Lin, 1991: 196 (brief description and color photo; sandy coastal waters around Taiwan) ; Li & Zhang, 1991 (part): 78–79, fig. 87 [brief description and illustration; China (Bohai Sea)]; Lindberg & Fedorov, 1993: 153 –156, fig. 52 [synonymy, description and illustration; Japan (Tokyo, Nagasaki, Misaki, Tsuruga, Ohama and Aomori), Korea (Pusan), China (Dalian, Sin-tsin, Qingdao and Shanghai), East China Sea )]; Kim & Kang, 1993: 102, 408 (description and color photo; Korea) ; Shen, 1993: 576, pl. 194(6) (synonymy, brief description and color photo; Taiwan) ; Masuda & Kobayashi, 1994: 405, fig. 2 [color photo; Japan (Izu Pen.); Tchang et al., 1994 (part): 286–287, fig. 177 [synonymy, description and illustration; China (Zhuanghe, Pikou, Qinhuangdao, Longkou, Yantai, Shidao, Qingdao and Shijiusuo)]; Kim & Youn, 1994: 121 –122, pl. 7(A) [synonymy, brief description and monochrome photo; Korea (Pusan and Yeosu)]; Nakabo, 1995: 204 –205 [pictorial key and color photo; Japan (Awaji I.)]; Li & Wang, 1995 (part): 238–241, fig. II-62-1 [synonymy, description and illustration; China (Dalian, Qingdao, Shenjiamen, Xiamen)]; Amaoka et al., 1995: 523 (brief description and color photos; northern Japan ) ; Su, 1995: 242 –243, fig. 299 (brief description and illustration; China); Yamada et al., 1995: 50, 206 (pictorial key and color photo; East China and Yellow Seas); Cheng, 1997: 453 –454, fig. 334 [synonymy, brief description and illustration; China (waters around Shandong Prov.)]; Suzuki & Kataoka, 1997: 243, pl. 138(733) [brief description and monochrome photo; Japan (Mie Pref.)]; Sanada, 1997: 72 [brief description and color photo; Japan (Seto Inland Sea)]; Sakamoto et al., 1997: 674 [brief description and color photos; Japan (Izu Pen.)]; Kim, 1997: 494 –495, pl. 46(189) [brief description, illustration and color photo; [Estuaries of Korea (Kunsan, Mokpo, Yeosu, Masan, Jinhae and Pusan)]; National Fisheries Research and Development Institute ( NFRDI), 1999: 184, 456, fig. 514 (description and color photo; Taiwan, East China Sea , Japan and Korea ) ; Yoshino, 1999: 247 (color photos; Japan); Nakabo, 2000: 1372 (pictorial key; Japan); Kim et al., 2001: 156, 288, fig. 467 (brief description and color photo; Korea); Shimizu, 2001: 44, 94, fig. 148 [monochrome photo; Japan (Iyo City)]; Wang, 2001: 310 –311, fig. 206 [synonymy, brief description and illustration; China ( Hebei Prov. )]; Wu, 2002: 603 –604, color fig. 73, fig. 435 [synonymy, brief description, color photo and illustration; China (Qingdao, Shanghai and Xiamen)]; Kim & Park, 2002: 413–414, brief description, color photo and illustration [Estuaries of Korea (Kunsan, Mokpo, Yeosu, Masan, Jinhae and Pusan)]; Youn, 2002: 438, 686 (synonymy and pictorial key, Korea) ; Myoung et al., 2002: 229 (brief description and color photos; Korea); Choi et al., 2002: 542 –543, color photo (Korea); Chen, 2003: 215, fig. 859 [color photo; Taiwan (Penghu Is.)]; Kim et al., 2004: 260 (brief description, pictorial key and color photo; Korea) ; Kim I. et al., 2005: 482, (brief description and color photo; Korea) ; Taki et al., 2005: 925 (brief description and illustration; Japan); Kim Y. et al., 2005: 288–289, fig. 489 (brief description and color photo; Korea) ; Yao & Yoshida, 2006: 68 (brief description and color photo; China); Zhao & Zhong, 2006: 47, 165–166, fig. 380 [brief description and color photo; China (Zhoushan)]; Ni & Wu, 2006: 818 –819, fig. 429 [synonymy; brief description and illustration; China (Lianyungang, Lusi, Yangtze River estuary and southern Yellow Sea)]; NFRDI, 2006: 336, fig. 558 (description and color photo; Taiwan, East China Sea , Japan and Korea ) ; Sokolovsky et al., 2007: 157 (illustration; Russian waters of the Japan Sea); Yamada et al., 2007: 1033 –1041, pl. 46(6) (pictorial key and color photo; East China and Yellow Seas); Choi, 2007: 267 (brief description and color photo; Korea) ; Konishi & Nakabo, 2007: 338 (brief description and color photos; Japan); NFRDI, 2008: 350, fig. 585 [description and color photo; northwestern Pacific ( Korea, Japan, East China Sea and Taiwan)]; Suzuki et al., 2009: 276 –291, fig. 1(d) (synonymy; description and monochrome photo; all around Japan) ; Sokolovsky et al., 2009: 324, 326: [brief description and color photo; Russia (Peter the Great Bay )]; Cao, 2010: 164 (brief description and illustration; China) ; Ishikawa & Senou, 2010: 331 [color photo; Japan (Fukushima)]; Yokogawa & Watanabe, 2011: 24 –32, fig. 1(a) [monochrome photo; Japan (Kii Channel)]; Zhang et al., 2011a: 51 –54 [ China (around Zhoushan)]; Ohashi & Motomura, 2011: 98 –99, fig. 28 [synonymy, brief description and color photos; Japan (northern Kagoshima Pref.)]; Choi et al., 2011: 158 (brief description and color photo; Korea) ; Uyeno & Sakamoto, 2011: 139, 299 (brief description and illustration; Sea of Japan, East China, Yellow, Bohai and South China Seas)]; Zhang et al., 2011b: 967 –972, fig. 1(upper photo) (color photo; East China Sea ); Shen & Wu, 2011: 746 (brief description and color photo; Taiwan) ; Chen & Yang, 2013: 317 (synonymy, brief description and color photo; Taiwan Strait); Nakabo & Doiuchi, 2013: 1676 (pictorial key; Japan); Igarashi & Ito, 2013: 9 –14 [ Japan (off Fukushima Pref.)]; Ito, 2013: 15–22 [ Japan (off Fukushima Pref.)]; Tsuji, 2013: 12, 20, fig. 64 [monochrome photo; Japan (Hakata I.)]; Liu et al. 2013: 250 –251 [description and color photos; China (southern Fujian Prov.)]; Jo & Myoung, 2013: 310 –311 (brief description and illustrations; Korea) ; Minami, 2014a: 1462 –1463 [description and illustration of larvae and juveniles; Japan (Seto Inland Sea, coastal waters of Honshu, Kyushu and Hokkaido), southern Korean Peninsula and the Yellow Sea]; Myoung et al., 2015: 257 (brief description and color photos; Korea) .

Pleuronichthys lighti: Wu, 1929: 66 , fig. 54 [original description and illustration; China (Amoy)]; Yokogawa et al., 2014: 385 – 392; Yokogawa, 2015; Yokogawa, 2016.

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

Pleuronichthys cornutus , honmeita-type: Nozawa & Kato, 1981: 1 –8, fig. 1(upper photo) [monochrome photo; Japan (off Tottori Pref.)]; Matsuoka et al., 1989: 23 –36, fig. 1(A) (color photo; East China and Yellow Seas); Watanabe et al., 1992: 2253 –2260 [ Japan (Kii Channel)]; Watanabe , 1994: 1–73, fig. 1(4) [illustration of larvae and juvenile; Japan (waters around Tokushima Pref.)]; 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-A type: Watanabe & Numachi, 1988: 765 –772 [ Japan (Kii Channel)].

Pleuronichthys sp. : Nakabo, 1995: 204–205 [pictorial key and color photo; Japan (Maizuru)]; Kim et al., 2001: 156, 288, fig. 468 (brief description and color photo; Korea); Kim Y. et al., 2005: 288–289, fig. 490 (brief description and color photo; Korea) .

Diagnosis. Scale length (trunk area) less than 1.23% of SL (Table 1), whole scale outline fan-shaped ( Fig. 3 A–C), exposed margin rhombic ( Fig. 4 A, B). Scales non-deciduous, longitudinal and vertical scale rows essentially regular ( Fig. 4 A, B). Upper eye area usually less than lower eye area, area ratio 0.70–1.08 (Table 1). Central longitudinal scales 88–105, scales below lateral line 59–74, abdominal vertebrae 12–14 (usually 13) (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 deep, rhombic or ovate, rather compressed, ocular and blind sides convex and almost flat, respectively.

Entire body covered with very small cycloid scales in essentially regular longitudinal and vertical scale rows ( Fig. 4 A, B). Scales basically fan-shaped ( Fig. 3 A–C), exposed margin rhombic ( Fig. 4 A, B), except on caudal peduncle (both sides), most blind side scales with sharp posterior margins ( Fig. 3 C). Scales deeply embedded, nondeciduous, entirely covered by thin tough pigmented epithelial membrane. 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, extremely protuberant. Upper eye usually scarcely posterior to and of less 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.

Dorsal and anal fin base very long. Dorsal fin anteriorly twisted toward blind side, originating from middle of upper eye position on blind side, 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 slender, ocular side fin longer than that on blind side, located at uppermost positions of gill slits on both sides. Pelvic fins small, blind side fin placed slightly more anterior to ocular side fin. Caudal and pelvic fin ray lengths (both sides) proportional to SL decreasing with growth, those of dorsal, anal 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), occasionally a short antrose branch from curve, running forward along supratemporal edge (Table 3).

Coloration. Ocular side fresh coloration variable ( Fig. 5 A–E), base color brown with a dark ( Fig. 5 A), red ( Fig. 5 B, E) or pale tinge ( Fig. 5 D), vermiculated with brown to dark-brown (occasionally rather pale) ( Fig. 5 D) blotches or spots, varying in size and density. Occasionally, such patterns rather modest, a fine dark mesh pattern surrounding scales ( Fig. 5 E). Some individuals with additional larger dark blotches with indistinct outline ( Fig. 5 B, E), or a broad ivory vertical band (sometimes indistinct) ( Fig. 5 C) posterior to opercle ( Fig. 5 B). Ocular side dorsal, anal and pelvic fins with similar blotches or spots, caudal membrane usually dark, pectoral fin usually with a broad blackish band distally. Blind side uniformly white to ivory, dorsal, caudal and anal fins dusky or dark distally, pectoral and pelvic fins white. Preserved specimens (formalin or alcohol) with ocular side base color more brownish, with darkish blotches but ivory post-opercular band mostly lost; blind side yellowish.

Distribution and habitat. Pleuronichthys lighti is broadly distributed in coastal waters around the Japanese archipelago (southward from southern Hokkaido) and along the entire coast of the Korean Peninsula, China and Taiwan, as well as occurring in offshore waters of the Bohai, Yellow and East China Seas, the latitudinal range extending from Peter the Great Bay ( Sokolovsky et al., 2009) (northern limit) to Hong Kong ( Shen, 1967) (southern limit). The species inhabits mainly sandy bottoms in shallow coastal waters, being relatively dominant over P. cornutus in Tokyo and Ise Bays, and the Seto Inland, Ariake and Yatsushiro Seas. It may also have some tolerance for reduced salinity, occasionally occurring in river estuaries in China ( Xu, 1990; Ni & Wu, 2006) and Korea ( Kim, 1997; Kim & Park, 2002) and brackish waters in Japan ( Hiyama & Yasuda, 1961, 1971).

Remarks. Until Suzuki et al.'s (2009) taxonomic revision, Pleuronichthys lighti had been regarded as a junior synonym of P. cornutus ( Wu, 1932; Wang, 1933; Zheng, 1955; Li and Wang, 1995; Evseenko, 2003, 2004), there being only a single taxon of " P. cornutus " recognized for East Asian Pleuronichthys . Suzuki et al. (2009), who formally indicated two taxa of East Asian Pleuronichthys , also regarded P. lighti as a junior synonym of their " P. cornutus " (common frog flounder), owing to their mis-identification of the P. cornutus lectotype. However, because the name P. cornutus has been transferred to the phantom frog flounder (new common name, see below), P. lighti should be resurrected as the valid name for the former ( Yokogawa et al., 2014).

Although some authors ( Reeves, 1927; Wu, 1929; Chu, 1931) credited P. lighti to Herre, there is no evidence for a species of this name described in Pleuronichthys by Herre ( Fowler, 1933; Eschmeyer, 2015). This suggests that P. lighti has been cited from unpublished or unavailable publication(s) authored by Herre. In this case, therefore, the author of this nominal taxon is regarded as Wu (1929), his publication being the first available description of the new taxon (ICZN 1999: Art 12.2). On the other hand, neither Reeves (1927) nor Chu (1931) provided a description, definition or indication of the status (ICZN 1999: Art. 12.1) of P. lighti . In addition, their material could not be identified as either of the two Pleuronichthys species.

Pleuronichthys lighti is clearly distinguished from P. cornutus by squamatological characteristics, including scale length ( SCL), scale shape, and counts of central longitudinal scales and scales below the lateral line (Table 1). For practical purposes, examination of scales removed from a specimen allows ready identification. For example, Shen's (1967) description of " P. cornutus " from Hong Kong included photographs of individual scales. Since they were clearly fan-shaped, the specimen could be readily identified as P. lighti . SCL proportions (% of SL) of 0.48– 0.92 (reciprocal numbers calculated from SCL proportion data), falling within the range for P. lighti (Table 1), supported that identification. On the other hand, when the removal of scales from a specimen is problematic, the exposed scale area index ( ESAI) substitutes for SCL, Yokogawa et al. (2014) demonstrating such in their reidentification of the P. cornutus lectotype using squamatological characteristics.

Other than squamatological characteristics, meristic counts of central longitudinal scales (CLS) and scales below the lateral line (SBL), which have no range overlap between P. lighti and P. cornutus (Table 1), are very useful for identification, being supported by eye area ratio, and proportions of ocular side pectoral fin length (% of SL) and inter-orbital ridge length (% of HL), which were new key characters proposed by Yokogawa (2015) (Table 1).

Youn (2002) provided a pictorial key for distinguishing between the two Pleuronichthys species, including "presence or absence of antrorse branch of SLL," and was followed by Suzuki et al. (2009), who emphasized that character as key for such identification. However, this is a variable condition, not clearly separating the two species (Table 3). In addition, the very deciduous nature of P. cornutus scales, resulting in frequent damage to landed P. cornutus individuals, results in difficulty in assessing the SLL character (blind side) [unclear in 46.5% of the total P. cornutus individuals examined by Watanabe et al. (1996b) (Table 3)]. In the present study also, an antrose branch of the SLL was unclear in 68.3% (ocular side) and 11.1% (blind side) of P. cornutus specimens (Table 3).

Although Suzuki et al. (2009) showed significantly lower percentages of an indistinct antrose branch in their specimens (Table 3), this may have simply reflected a high proportion of well-fixed undamaged specimens in their material examined. Although Table 3 suggests specific trends in the presence / absence of an antrose branch of the SLL, the condition is clearly variable and obscured by the likelihood of damage to specimens. In conclusion, the SLL character is impractical for identification of the two species.

Suzuki et al. (2009) also emphasized counts of dorsal and anal fin rays (DFR and AFR) as diagnostic characters, frequently using them for specific identification of literature records of Pleuronichthys species. However, the ranges of these meristics for the two Pleuronichthys species broadly overlap ( Table 5 ). In addition, some inter-populational differences have been suggested ( Yamada et al., 2007). Although DFR and AFR counts in Suzuki et al. (2009) (based on specimens predominantly from Japan) suggested some separation of the two species [DFR: 72–88 vs. 67–80; AFR: 52–65 vs. 48–59 for P. lighti (= their P. cornutus ) and P. cornutus (= their P. japonicus ), respectively], Yamada et al. (2007), examining both Japanese and non-Japanese specimens, found far greater count overlaps [DFR: 68–89 vs. 65–83; AFR: 50–69 vs. 50–59 for P. lighti (= their P. cornutus ) and P. cornutus (= their P. sp.)]. Therefore, only a few individuals at the extreme ranges of DFR and / or AFR counts may be unequivocally identified as one or other species.

Pleuronichthys lighti Pleuronichthys cornutus

1 Count tends to increase with growth in P. cornutus .

On the other hand, differences in counts of abdominal vertebrae (AV) between the two Pleuronichthys species are significant (Tables 1, 2), with little range overlap (Table 2). However, being an internal character, it is problematic on practical grounds.

Blind side colored individuals have been reported for P. lighti , some specimens having all or part of the blind side colored similarly to the ocular side, with both sides generally convex ( Yamada, 1969). Such individuals may not be so rare in the field, comprising 9.2% of 195 specimens from the Yellow Sea, for example ( Yamada, 1969). They also appeared in higher percentages during artificial production ( Kitajima et al., 1987). In addition, ocular side albinism individuals are also common in this species ( Kitajima et al., 1987; Sakamoto et al., 1997).

Kim & Youn (1994) described P. lighti (as P. cornutus ) from Korea, based on 12 specimens, noting almost equal pectoral fin lengths on both sides (repeated in Kim, 1997). However, the ocular side pectoral fin was found to be clearly longer than that on the blind side in the present study (Table 1).

Because squamation and ocular side coloration are generally useful for distinguishing between the two Pleuronichthys species, many of the " P. cornutus " literature records including photograph(s) and / or illustration(s) could be specifically identified as P. lighti (see synonymy above). Similarly, photographs of Pleuronichthys sp. from Maizuru, Japan, in Nakabo (1995), but strangely omitted by Suzuki et al. (2009), and Korean specimens of P. sp. in Kim Y. et al. (2001, 2005) were considered as this species.

Suzuki et al. (2009) and Nakabo & Doiuchi (2013) questioned the identification of a photographed specimen of " P. cornutus " (= P. lighti ) in Amaoka et al. (1995), regarding it as P. japonicus (= P. cornutus ) due to its similar color pattern to that species ( Fig. 5 H). However, the identification by Amaoka et al. (1995) is here considered to have been correct, the longitudinal and vertical scale rows of the specimen following regular patterns, and the CLS count determined from the photograph being ca. 94 (within the range of P. lighti ) (Table 1).

On the other hand, color photographs of " P. cornutus " in Ueno (1981) ( Japan) , Iwai & Ito (1986) ( Japan), Chen et al. (1997) ( southern China ), Sakamoto (1998) ( Japan) and Lei et al. (1999) ( Macao) were not identifiable due to ambiguous ocular side coloration and unclear squamation, in addition to a lack of any additional morphological data.

A number of descriptions of " P. cornutus " have included lateral line scale (LLS) counts, that were consistent with the range of this species ( Table 5 ), i.e., 100–108 ( Starks & Thompson, 1910), 95 ( Wang, 1933), 98–110 ( Norman, 1934), 93–118 ( Okada et al., 1935), 93–118 ( Chyung, 1954, 1977), 93–118 ( Okada, 1955), 98–110 ( Zheng, 1962), 92–102 ( Tchang & Wang, 1963), 92–105 ( Fitch, 1963), 97–103 (Ochiai, 1965), 97–103 ( Masuda et al., 1975), 98–110 ( Shen, 1982, 1984a, 1993), 98–110 ( Chen & Yu, 1984), 104 ( Matsuura, 1985), 103–109 ( Miao, 1985), 92–113 ( Chen, 1987), 98–101 ( Xu, 1990), 102–106 ( Lindberg & Fedorov, 1993), 93–118 ( Kim & Kang, 1993), 92–102 ( Cheng, 1997), 92–102 ( Wang, 2001), 103–109 ( Wu, 2002), 100–125 ( Kim et al., 2004), 93–118 ( Kim I. et al., 2005), 103–109 ( Ni & Wu, 2006), 98–110 ( Sokolovsky et al., 2009), 103–109 (Chen & Yang, 2013) and 98–110 ( Liu et al., 2013). Because other meristic counts included (e.g., DFR and AFR) also conformed to the ranges of P. lighti (see summary of Yamada et al., 2007), the materials on which the above were based are regarded as that species.

Although Hubbs' (1915) description of " P. cornutus " did not record LLS counts, it included raw measurement data of some body regions for 7 specimens from Swatow , China and waters near Kagoshima , Japan. Calculated proportions from that data for ocular side pectoral fin length and upper eye horizontal diameter resulted in 9.4–15.9 % of SL (average 12.9) and 29.2–33.3 % of HL (average 31.5), respectively, both corresponding closely with figures for P. lighti (Tables 1, 4), which species they apparently represented.

However, the specific identities of specimens listed as " P. cornutus " in the following, could not be determined due to the lack of morphological information: Rutter (1897) [China (Swatow)], Jordan & Starks (1904, 1905) [ Japan ( Suruga Bay ) and Korea], Smith & Pope (1906) [ Japan (Kagoshima and Yamagawa)] , Jordan et al. (1913) [ Japan (Hakodate to Nagasaki)] , Jordan & Metz (1913) [Korea (Fusan)], Reeves (1927) [ China (Swatow, Amoy)], Mori (1928) [Korea (Fusan)], Fowler (1929) ( Hong Kong), Chu (1931) ( China), Schmidt (1931a) [ Japan (Obama)], Schmidt (1931b) [ Japan (Nagasaki and Misaki) and Korea (Fusan)], Schmidt (1931c) [ Korea (Fusan)], Okada & Matsubara (1938) ( Japan, China, Korea and Taiwan), Kuronuma (1940) [ Japan (from Hokkaido to Kyushu)], Herre (1945) [ China (Tinghai and Hong Kong)], Mori (1952), [Korea (Fusan, Kunsan)], Matsubara (1955), ( Japan, Korea, Taiwan and China), Mori (1956) [ Japan (Kasumi and Hamada)], Kamohara (1964) [ Japan (Kochi Pref.)], Hayashi & Ito (1974) [ Japan (Sagami Bay)], Fuwa (1976) [ Japan (Shibushi Bay)], Hayashi & Nishiyama (1980) [ Japan ( Sagami Bay )], Yoo & Lee (1995) (recorded as Pleuronichthys cornuta ) [Korea (Cheju I.)], Sokolovskaya et al. (1998) [ Russia (Peter the Great Bay )], Amaoka (2000) ( South China Sea ), Evseenko (2003, 2004) [ Russia (Peter the Great Bay ) and western North Pacific ], Chen (2004) [ Taiwan (Penghu Is.)], Shao et al., (2008) ( northern South China Sea ) .

Notwithstanding the unknown specific identities of " P. cornutus " material, the following reports are considered likely to include at least P. lighti , due to the dominance of that species over P. cornutus at their collection localities (including regions around Tokyo and Ise Bays, and the Seto Inland Sea): Steindachner (1896) [ Japan (Kobe or Nagasaki)], Jordan & Snyder (1900, 1901) [ Japan (Hakodate, Tokyo and Yokohama)], Snyder (1912) [ Japan (Hakodate, Tokyo and Tsuruga)], Jordan & Thompson (1914) [ Japan (Osaka and Misaki)], Matsuura & Izuka (1920) [ Japan (Takamatsu)], Jordan & Hubbs (1925) [ Japan (Tokyo, Kobe, Toba, Kagoshima, Mikawa Bay, Misaki and Fukui)], Kataoka & Tomida (1981) [ Japan (various sites around Mie Pref.)].

On the other hand, although records of " P. cornutus " by Shinohara et al. (2001) [ Japan ( Tosa Bay )] and Hagiwara & Kimura (2005) [ Japan (Tateyama Bay)] were presently not identifiable, they can be identified when examining their registered museum (voucher) specimens listed therein.

Regarding other synonymies, although Bleeker (1854 –57, 1859) listed " Platessa cornuta " (listing material from Nagasaki, Japan in each case), the latter could not be identified as either of the two Pleuronichthys species owing to insufficient morphological information. The genus Heteroprosopon , which was established by Bleeker (1862) for a monotypic taxon ( Platessa cornuta ), is regarded as a synonym of Pleuronichthys , potentially including either or both of the two Pleuronichthys species considered here.

Specimens comprising " Parophrys cornuta ," recorded by Günther (1862) and Otaki (1897), were identifiable as Pleuronichthys lighti due to the respective descriptions and illustrations of their ocular side coloration patterns. Nyström's (1887) specimens, however, were identified on the basis of 61 AFRs, a count peculiar to P. lighti ( Table 5 , see also Yamada et al., 2007). Günther's (1880) specimens, collected from Kobe (Seto Inland Sea), where P. cornutus does not occur, must therefore have been P. lighti , whereas specimens reported by Bleeker (1872) (China), and Namiye (1881) and Ishikawa & Matsuura (1897) (both Niigata, Japan) are now unidentifiable due to a lack of specific information.

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).

Tables

TABLE 5. Meristic counts of two Pleuronichthys species (other than those shown in TABLE 1).

	Range	Average	Range	Average
Dorsal fin rays	71–83	77.69	67–81	74.24
Caudal fin rays	18–20	19.07	18–20	19.11
Anal fin rays	50–62	57.28	48–58	53.63
Pectoral fin rays (ocular side)	9–13	10.94	9–13	10.92
Pectoral fin rays (blind side)	9–13	10.81	9–12	10.38
Pelvic fin rays (ocular side)	5–7	6.05	6–7	6.02
Pelvic fin rays (blind side)	5–7	5.98	5–6	5.98
Upper limb gill rakers 1	2–4	2.70	2–4	2.70
Lower limb gill rakers 1	4–7	5.42	4–7	5.40
Total gill rakers 1	6–11	8.12	6–11	8.10
Caudal vertebrae	23–26	24.25	23–25	24.24
Total vertebrae	36–39	37.24	35–37	36.29