Pseudorhombus elevatus Ogilby, 1912

Matsunuma, Mizuki, Tashiro, Fumihito & Motomura, Hiroyuki, 2024, First Japanese Records of the Flounders Pseudorhombus elevatus and P. quinquocellatus (Teleostei: Paralichthyidae) from Okinawa Island, Ryukyu Islands, Species Diversity 29 (1), pp. 9-21 : 10-18

Pseudorhombus elevatus Ogilby, 1912

[English name: Deep Flounder; new standard Japanese name: Maru-ganzō-birame] ( Figs 1 , 2A, B , 3A, B , 4A, B , 5A ; Table 1)

Pseudorhombus elevatus Ogilby, 1912: 45 (type locality: Bulwer, Moreton Bay, Queensland, Australia); Chabanaud 1929: 376 (Nha Trang, Vietnam; listed); Punpoka 1964: 23, fig. 5 (Gulf of Thailand; description); Shen 1983: 9, fig. 8 ( Taiwan; short description); Li and Wang 1995: 141, fig. II-16 (Hainan Island to Taiwan; description and synonymy); Shen and Wu 2011: 743, unnumbered fig. ( Taiwan; atlas); Ng et al. 2015: 320, fig. 1a ( Singapore; checklist with voucher specimen photograph); Voronina et al. 2016: 392, fig. 3A ( Vietnam; short description and synonymy); Mohd Sharol and Seah 2020: 95, unnumbered fig. (Bidong Island, Terengganu, Malaysia; short description).

Pseudorhombus pentophthalmus not of Günther: Shen 1983: 7, fig. 4 (in part; Taiwan; short description).

Japanese specimens. Thirty-five specimens, 31.5– 147.2 mm SL: FAKU 101405, 109.7 mm SL, FAKU 101406, 127.9 mm SL, Naha, Okinawa Island, Ryukyu Islands , March 1970; HUMZ 107788, 135.1 mm SL, obtained at Chinen fishing port, Nanjo , Okinawa Island, K . Nishida , gill net, 23 April 1986; KAUM –I . 55230, 118.4 mm SL, KAUM –I. 55231, 109.9 mm SL, KAUM –I. 55232, 108.3 mm SL, KAUM –I. 55233, 115.1 mm SL, KAUM –I. 55234, 120.6 mm SL, KAUM –I. 55235, 135.7 mm SL, KAUM –I. 55236, 119.6 mm SL, KAUM –I. 55237, 123.9 mm SL, KAUM –I. 55602, 35.3 mm SL, KAUM –I. 55626, 37.0 mm SL, KAUM –I. 55636, 31.9 mm SL, KAUM –I. 55637, 34.1 mm SL, KAUM –I. 55638, 38.9 mm SL, KAUM –I. 55639, 32.7 mm SL, KAUM –I. 55640, 36.0 mm SL, KAUM –I. 55641, 41.1 mm SL, KAUM –I. 55642, 33.7 mm SL, KAUM –I. 55643, 37.4 mm SL, KAUM –I. 55644, 32.3 mm SL, KAUM –I. 55647, 39.9 mm SL, KAUM –I. 55648, 37.7 mm SL, KAUM –I. 55649, 31.9 mm SL, KAUM –I. 55651, 39.9 mm SL, KAUM –I. 55652, 31.5 mm SL, KAUM –I. 55653, 34.5 mm SL, KAUM –I. 55655, 41.0 mm SL, KAUM –I. 55656, 39.0 mm SL, Nakagusuku Bay, Okinawa Island, 26°15′N, 127°49′E, 17–41 m depth, Okinawa Prefectural Fisheries Experimental Station ( OPFES), bottom trawl, 1970–1971 (17 September 1970, 20 April 1971 or 10 June 1971); OCF-P 10718 (formerly part of URM-P 19977 ), 131.1 mm SL, OCF-P 10719 (formerly part of URM-P 19977 ), 121.5 mm SL, Nakagusuku Bay , Okinawa Island, OPFES, bottom trawl, 1969–1972; URM-P 11139, 106.7 mm SL, obtained at Chinen Fishing Port, Nanjo, Okinawa Island, N . Shikatani, 17 July 1985; URM-P 18509, 144.5 mm SL, URM-P 18510, 147.2 mm SL, obtained at Chinen Fishing Port, Nanjo , Okinawa Island, N . Shikatani and T . Fuse , 6 December 1986 .

Comparative specimens. Nineteen specimens, 68.9– 125.5mm SL: BSKU 98047 , 92.0mm SL, Sepanggar Bay , Kota Kinabalu , Malaysia, bottom trawl; FAKU S298 , 99.6mm SL, no data (possibly from South China Sea ); FRLM 51675 , 87.4mm SL, off Bidong Island, Terengganu, Malaysia, 05°36′43″N, 103°08′32″E, 35m depth, bottom trawl, 30 September 2015; FRLM 51773, 120.3 mm SL, off Bidong Island, Terengganu, Malaysia, 05°36′43″N, 103°08′32″E, S . Kimura and R . Matsuo , bottom trawl, 1 October 2015; FRLM 55070 , 85.1mm SL, off Bidong Island, Terengganu, Malaysia, 05°38′27″N, 103°07′16″E, bottom trawl, 14 August 2017; FRLM 55295 , 97.0mm SL, obtained at Pulau Kambing, Kuala Terengganu, Terengganu, Malaysia, 17 August 2017; HUMZ 46943 , 118.0 mm SL, HUMZ 46944, 124.8 mm SL, northwest of Borneo, 03°00′N, 109°15′E, 56m depth, RV Oshoro-maru, 13 November 1975; HUMZ 105338 (formerly AMS IB 654 ), 91.7mm SL, HUMZ 105339 (formerly AMS IB 6545 ), 115.1 mm SL, off Townsville, Queensland, Australia, 19°16′S, 146°49′E, July 1963; KAUM –I . 105148, 110.5mm SL, off east coast of Bidong Island , Terengganu, Malaysia, 05°37′18″N, 103°06′43″E, 30m depth, RV Discovery, bottom trawl, 14 August 2017; MNHN 1999-0311 , 125.5mm SL, MNHN 2016-0315 , 2 specimens, 99.0– 109.2mm SL, Nha Trang , Vietnam, 12°15′00″N, 109°10′01.2″E, 10 February , 1926; MNHN 1999-0312 , 68.9mm SL, Hue, Vietnam, 16°28′01.2″N, 107°36′00″E, 15 July 1926; MNHN 2016-0314 , 102.8mm SL, 6 miles east of Hao Tao Islands, Vietnam, 12°30′00″N, 112°30′00″E, 25–33m depth, 8 April 1927; QM I . 1569 (formerly AFAQ 1713 ) (photograph only examined), holotype of P . elevatus, 120.5 mm SL, Bulwer, Moreton Bay , Queensland, Australia, J . Palmer; ZMA .

PISC.115232, 2 specimens, 99.5–99.8mm SL, off Parangipettai [Porto Novo], India, Bay of Bengal, N . Ramanathan, 1976.

Description. Counts and measurements (% of SL) given in Table 1. Body oval, moderately deep, strongly compressed; dorsal and ventral contours almost symmetrical ( Fig. 1A, B ). Caudal peduncle moderately deep, very short. Head moderately large; dorsal profile along dorsal-fin base and snout with distinct notch at dorsal-fin origin (viewed from ocular side), notch more obvious in small specimens <50 mm SL. Eye moderately large, upper eye usually larger than lower eye (upper orbit diameter 95%–131% of lower orbit diameter), wide space between upper orbit rim and dorsal profile of head (dorsal-fin base); interorbital region very narrow, separated by low bony ridge. Snout relatively short, its length slightly less than orbit diameter; frontal contour of snout well-rounded, not protruding; profile of bulge on snout to upper orbit rim with notch just in front of anterior margin of upper orbit (snout bulge strongly expanded dorsally). Ocular-side nostrils close to each other; anterior nostril tubular, with short triangular flap on posterior margin of tube, its tip reaching posterior nostril when depressed; posterior nostril with low skin rim. Blind-side nostrils smaller and similar to those on ocular side; anterior nostril with short, triangular flap. Mouth relatively small, oblique (at angle of ca. 50° to body axis); upper-jaw length greater than eye diameter (upper-jaw length 134%–170% of upper orbit diameter); posterior part of maxilla enlarged; bulge on anterior tip of mandible small, strongly protruding. Teeth minute, conical, sharply pointed, slightly larger on lower jaw ( Fig. 2A, B ); uniserial on both jaws; anterior teeth slightly larger than posterior teeth, neither caniniform nor strongly curved; vomer toothless. Gill rakers on outer surface of gill arches moderately long, with sharp tips ( Fig. 3A, B ); inner surface of each raker with small serrae, 2nd lower gill raker with 4–17 serrae (number increasing with growth); 0–2 and 0 or 1 rudimentary rakers on upper and lower arches, respectively, on ocular side. No skin flaps on eye surfaces. Gill opening below pectoral-fin base, with low skin fold not forming distinct flap. 1st interhaemal spine usually projecting through body wall near anal-fin origin.

Scales. Scales moderately large, strong, not deciduous, cycloid on blind side, ctenoid on ocular side; squamation on snout highly variable, completely naked, or ctenoid scales present around orbit rims and on interorbital region; mid-interorbital region always naked; posterior interorbital region surrounded by infraorbital canal (lower eye) and posterior portions of orbit rims very broad, covered entirely by 7–40 small ctenoid scales (number increasing with growth). Maxilla entirely covered with ctenoid scales. Pectoral fin and base usually naked. Ocular and blind surfaces of dorsal- and anal-fin rays generally with single row of small ctenoid scales, sometimes cycloid or weakly ctenoid on blind side; last 6–8 rays of both fines naked. Ocular surface of each ocular-side pelvic-fin ray usually with single row of small ctenoid scales, blind side surface naked; blind-side pelvic-fin rays naked on both surfaces; all pelvic-fin rays entirely naked in small specimens (<50 mm SL). Caudal-fin rays with 2 or 3 rows of ctenoid scales. Posterior margin of trunk lateral-line scales with ctenii. Tubular part of trunk lateral-line scales with single branch (cutaneous canaliculus) directed upward or downward (rarely two branches directed both upward and downward); scales on curved section usually with upwardly directed branches; on straight section, alternative branch openings present almost equally (e.g., three upwardly directed branches followed by three downwardly directed branches); cutaneous canaliculus of trunk lateral-line scales on blind side weakly developed.

Fins. Dorsal-fin origin (1st dorsal-fin ray base) just above or slightly anterior to blind-side anterior nostril, sometimes slightly posterior to but not level with interspace between nostrils or above posterior nostril ( Fig. 4A, B ); 1st ray connected with blind side of body with large skin wall, its origin extending above posterior nostril; 1st to 3rd rays detached with membrane but not strongly elongated. Anal fin similar in size to dorsal fin, its origin below upper origin of pectoral-fin base on ocular side. All rays of dorsal and anal fins unbranched. Pectoral fins unequal in size, ocular side fin slightly longer than blind side fin (ocular-side pectoral-fin length 116%–156% of blind-side pectoral fin length); usually uppermost 2 and lowermost rays unbranched, remaining rays branched; 4th or 5th ray longest (ocular side), its tip extending slightly beyond trunk lateral line. Pelvic-fin origins at same level, below corner of preopercle; fins moderate in size, 2nd ray longest, its tip extending beyond anal-fin origin when depressed; anteriormost 2 or 3 rays unbranched, remaining rays branched. Caudal fin moderately large, double truncate with 14 branched rays.

Lateral line. Lateral line on trunk with curved section above pectoral fin, thereafter immediately dropping downward and running straight along mid-body axis, extending onto caudal fin; depth of curved section 8%–12% of standard length. Supratemporal canal developed on both sides, reaching below 7th to 10th dorsal-fin ray base on ocular side. Preoperculo-mandibular canal continuous. Infraorbital canal developed along both orbit rims, that around lower eye terminating just in front of anterior margin of lower orbit, that around upper eye extending anteriorly to below 3rd to 5th dorsal-fin ray base.

Coloration. Head and body uniformly creamy-white to brown; most markings obscured following preservation of specimens ( Fig. 1A, B ). Following description based on well-marked preserved specimens. Large specimens (> 100 mm SL) with 3 dark blotches along trunk lateral line; anteriormost blotch largest (similar to orbit size), circular, at junction of curve and straight sections of lateral line; middle blotch smallest, near mid-point of lateral-line straight section; posteriormost blotch moderately large, oval, somewhat elongate vertically, level with ends of dorsal- and anal-fin bases. Two rows of dark rings and crescentic blotches both above and below lateral line. Similar dark markings scattered on head, and dorsal and anal fins. Caudal fin with a pair of dark blotches on basal half. In small specimens examined (<50 mm SL), most body scales lost and markings indeterminate, but a single large blotch at mid-point of body (junction of curved and straight sections of lateral line) usually retained ( Fig. 1B ). Fresh coloration of Japanese specimens not recorded (but see Fig. 1C ).

Distribution. Pseudorhombus elevates is widely distributed in the Indo-West Pacific region, including the Red Sea, from the east coast of Africa throughout the IndoAustralian Archipelago, and from Australia (type locality: Queensland) northward to the Ryukyu Islands, Japan ( Amaoka and Hensley 2001; Voronina et al. 2016; Psomadakis et al. 2019; Hensley and Amaoka 2022; this study). The present specimens from Okinawa Island represent the first Japanese record of the species, the previous northernmost records having been reported from Taiwan (see Li and Wang 1995; Shen and Wu 2011). Comparative specimens were collected from relatively shallow depths of 25– 56 m. The Japanese specimens were collected from Nakagusuku Bay (26°15′N, 127°49′E), east coast of Okinawa Island, from 17–41 m depth during experimental bottom-trawling surveys or obtained at local fish markets on the island.

Remarks. Following the key to species of Pseudorhombus in the western Pacific Ocean in Amaoka and Hensley (2001), the present non-type specimens were identified as P. elevates , characterized by the following combination of characters: 67–73 dorsal-fin rays, 49–56 anal-fin rays, gill rakers long and pointed ( Fig. 3A, B ), ocular-side of body covered with ctenoid scales, blind-side of body covered with cycloid scales, anterior dorsal-fin rays not elongated, first dorsal-fin ray base situated above or slightly anterior to blind-side anterior nostril, and upper profile of snout with a distinct notch just front of upper eye.

Comparisons of selected diagnostic features, and prominent ocelli and blotch patterns, between Japanese species of Pseudorhombus are summarized in Table 2 and Fig. 5 (see also Supplementary Fig. 1 ), respectively. A comparison with Japanese congeners showed P. elevatus clearly differed from P. dupliciocellatus , P. oculocirris , P. pentophthalmus and P. quinquocellatus by having three blotches along the straight section of the lateral line on the ocular side [see Fig. 1C , for fresh coloration of a Malaysian specimen; Figs 1A, B , 5A , for anteriormost (largest) blotch usually retained in preserved specimens], whereas the ocular-side body had one or two pairs of double ocelli above and below the lateral line (usually three ocelli) in P. dupliciocellatus ( Fig. 5I ), and two pairs of ocelli above and below the lateral line, with one ocellus on the posterior third of the straight lateral-line section (total five ocelli) in P. oculocirris , P. pentophthalmus and P. quinquocellatus ( Fig. 5F, G, H ) ( Table 2; see also Amaoka 2016). Pseudorhombus elevatus also clearly differed from P. oligodon in having the blind-side body mostly covered with cycloid scales (vs. ctenoid in P. oligodon ), and from P. arsius in lower gill-raker numbers [14–24 in P. elevatus vs. 8–15 in P. arsius ; see Amaoka and Hensley (2001)] and numerous minute teeth on both jaws ( Fig. 2A, B ) (vs. large canines anteriorly on both jaws in P. arsius ). Moreover, P. elevatus differed from P. cinnamoneus and P. levisquamis , having fewer dorsal- and anal-fin rays [67–73 and 49–56, respectively, in P. elevatus vs. 80–85 and 61–67, respectively, in P. cinnamoneus , and 79–89 and 59–67, respectively, in P. levisquamis ; see Amaoka and Hensley (2001)].

Specimens of Pseudorhombus with five ocelli, figured as P. elevatus in Fishes of Southern Taiwan ( Amaoka 2019, 2020), were re-identified here as an unidentified species, morphologically similar to P. oculocirris , the taxonomic status of the former currently being studied by our group. Although blotches were obscured in the holotype of P. elevatus ( Fig. 1D ), Ogilby (1912) described the specimen as possessing “a large dark spot behind the angle of the lateral line and five series of inconspicuous ocelli, two above, one on and two below the lateral line” on the ocular-side body. Such characteristics were consistent with the present specimens of P. elevatus and have been described and figured for the species in previous studies, including Norman (1934), Amaoka and Hensley (2001) and Hensley and Amaoka (2022).

Standard Japanese name. The standard Japanese name, “Maru-ganzō-birame”, is newly proposed for P. elevates , based on KAUM–I. 55230 ( Fig. 1A ), being derived from the deep body (“maru” = circular; “ganzō-birame”= Japanese common name of Pseudorhombus ).

Pseudorhombus quinquocellatus Weber and de Beaufort, 1929 [English name: Five-eyed Flounder; new standard Japanese name: Niten-ganzō-birame] ( Figs 2C , 3C, D , 4C , 5F , 6A–D , 7 ; Table 1)

Pseudorhombus quinquocellatus Weber and de Beaufort, 1929: 104 (type locality: Madura Strait and Kangean Islands, Indonesia); Norman 1934: 108, fig. 66 (Nha Trang Bay, Vietnam; description and synonymy); Punpoka 1964: 27, fig. 6 (Gulf of Thailand; description); Shen 1967: 173, figs 17–20 (Kowloon, Hong Kong; description); Shen 1983: 9, fig. 9 ( Taiwan; short description); Li and Wang 1995: 135, fig. II-13 (Hainan Island to Taiwan; description and synonymy); Shen and Wu 2011: 745, unnumbered fig. ( Taiwan; atlas); Amaoka 2019: 1210, unnumbered figs ( Taiwan; short description); Amaoka 2020: 1210, unnumbered figs (ditto).

Japanese specimens. Two specimens, 46.3–55.5 mm SL: KAUM –I . 55592, 46.3 mm SL, Nakagusuku Bay, Okinawa Island, 26°15′N, 127°49′E, 17–41 m depth, OPFES, bottom trawl, 1970–1971 (17 September 1970, 20 April 1971 or 10 June 1971); OCF-P 10720 (formerly part of URM-P 19977 ), 55.5 mm SL, Nakagusuku Bay , Okinawa Island, OPFES, bottom trawl, 1969–1972 .

Comparative specimens. Nine specimens, 108.4– 186.1 mm SL: HUMZ 46811, 186.1 mm SL, northwest of Borneo , 03°35′N, 109°03′E, 82 m depth, RV Oshoro-maru, 11 November 1975; HUMZ 46847, 165.6 mm SL, northwest of Borneo, 03°37′N, 109°14′E, 80 m depth, RV Oshoro-maru, 11 November 1975; HUMZ 46869, 167.4 mm SL, northwest of Borneo, 03°40′N, 109°25′E, 84 m depth, RV Oshoro-maru, 11 November 1975; KAUM –I . 44649, 126.4 mm SL, KAUM –I. 110818, 108.4 mm SL, KAUM –I. 113356, 121.7 mm SL, KAUM –I. 115381, 121.4 mm SL, obtained at fishing port at Donggang, Pingtung, Taiwan, bottom trawl; ZMA . PISC .109328, syntype of P. quinquocellatus , 153.5 mm SL, Madura Strait , Indonesia, 07°39′S, 114°17′E, 45–55 fathoms (ca. 82–101 m) depth, “Gier no. 13, Exp. No. 5, 1110”, 8 September 1908; ZMA. PISC.112569, syntype of P . quinquocellatus, 150.1 mm SL, Madura Strait , Indonesia, 07°39′S, 114°18′E, 43–55 fathoms (ca. 79–101 m) depth, “Gier no. 13, Exp. no. 6, 1296”, 9 November 1908 .

Description. Counts and measurements (% of SL) given in Table 1. Body oval, elongate, moderately deep, strongly compressed; dorsal and ventral contours almost symmetrical ( Fig. 6A ). Caudal peduncle moderately deep, very short. Head moderately large; dorsal profile along dorsal-fin base and snout with shallow notch at dorsal-fin origin (viewed from ocular side). Eye large, upper eye larger than lower eye (upper orbit diameter 116%–119% of lower orbit diameter); relatively narrow space between upper orbit rim and dorsal profile of head (dorsal-fin base); interorbital region very narrow, separated by low bony ridge. Snout relatively long, its length subequal to orbit diameter; frontal contour of snout weakly pointed, protruding from head contour; bulge on snout not well expanded from dorsal contour of snout to upper orbit rim. Ocular-side nostrils not so close to each other; anterior nostril tubular, with relatively long, triangular flap on posterior margin of tube, its tip just reaching posterior nostril when depressed; posterior nostril with low skin rim. Blind-side nostrils smaller and similar to those on ocular side; anterior nostril with long, triangular flap. Mouth relatively large, oblique (at angle of ca. 40° to body axis); upper-jaw length distinctly greater than eye diameter (upper-jaw length 141%–143% of upper orbit diameter); posterior part of maxilla enlarged; bulge on anterior tip of mandible small, not strongly protruding. Teeth relatively large, conical, sharply pointed, slightly larger on lower jaw; lower-jaw teeth and anterior teeth on upper jaw enlarged, caniniform, canted backward and inward ( Fig. 2C ); uniserial on both jaws; vomer toothless. Gill rakers on outer surface of gill arches moderately long, with sharp tips, relatively few in number, well-spaced from each other ( Fig. 3C ); inner surface of each raker with small serrae, 2nd lower gill raker with 6 serrae; 0 or 1 and 0 rudimentary rakers on upper and lower arches, respectively, on ocular side. No skin flaps on eye surfaces. 2 distinct flaps along gill opening below pectoral-fin base on ocular side ( Fig. 7 ). 1st interhaemal spine usually projecting through body wall near anal-fin origin.

Scales. Scales moderately large, strong, not deciduous, cycloid on blind side, ctenoid on ocular side; snout and mid-interorbital region naked; posterior interorbital region surrounded by infraorbital canal (lower eye) and posterior portions of orbit rims relatively narrow, covered by 13–17 small ctenoid scales. Maxilla damaged in both specimens, posterodorsal portion partly scaled. Pectoral fin and base naked. Ocular surface of dorsal- and anal-fin rays with single row of small ctenoid scales, blind side surface with single row of weakly ctenoid or cycloid scales. Pelvic-fin rays naked in small Japanese specimens. Scales on caudal fin completely lost due to damage. Tubular part of trunk lateral-line scales with single, very short branch (cutaneous canaliculus) directed upward or downward; scales on curved section usually with upwardly directed branches; on straight section, alternative branch openings present almost equally; cutaneous canaliculus weakly developed or absent on blind-side lateral line and posterior portion of ocular-side lateral-line scales.

Fins. Dorsal-fin origin (1st dorsal-fin ray base) just above blind-side anterior nostril ( Fig. 4C ); 1st ray connected to blind side of body with large skin wall, its origin above posterior nostril; 1st to 3rd rays detached with membrane (based on OCF-P 10720; damaged in KAUM–I. 55592) but not strongly elongated. Anal fin similar in size to dorsal fin; its origin below upper origin of pectoral-fin base on ocular side. All rays of dorsal and anal fins unbranched. Pectoral fins unequal in size, ocular-side fin slightly longer than blind side fin (ocular-side pectoral-fin length 129%–131% of blind-side pectoral-fin length); uppermost 2 and lowermost rays unbranched, remaining rays branched; 5th ray longest (ocular side), its tip extending slightly beyond trunk lateral line. Pelvic-fin origins at same level, below corner of preopercle; fins moderate in size, 2nd ray longest, its tip extending beyond anal-fin origin when depressed; anteriormost 2 rays unbranched, remaining rays branched. Caudal fin damaged in both specimens.

Lateral line. Lateral line on trunk with curved section above pectoral fin, thereafter immediately dropping downward and running straight along mid-body axis, extending onto caudal fin; depth of curved section 8%–10% of standard length. Supratemporal canal developed on both sides, reaching below 8th dorsal-fin ray base on ocular side (KAUM–I. 55592). Preoperculo-mandibular canal continuous. Infraorbital canal developed along both orbit rims, that around lower eye terminating near ventral edge of lower orbit rim; that around upper eye extending anteriorly to below 5th dorsal-fin ray base.

Coloration. Head and body uniformly creamy-white ( Fig. 6A ); 5 pale (but obvious) large, dark ocellated spots on ocular side, pairs of 2 spots above and below lateral line, and single spot on lateral line (near mid-point of straight section), size of ocellated spots subequal to orbit; about 6 and 4 dark rings, respectively, along dorsal and ventral portions of body on ocular side. Markings on dorsal, anal and caudal fins unable to be determined due to damage. Fresh coloration of Japanese specimens not recorded (but see Fig. 6B ).

Distribution. Pseudorhombus quinquocellatus is distributed in the eastern Indian and western Pacific oceans, from the Andaman Sea east to New Guinea and northeastern Australia, and north to southern Japan (Okinawa Island) ( Amaoka and Hensley 2001; Psomadakis et al. 2019; this study). The present specimens from Okinawa Island represent the first Japanese record of the species, the previous northernmost records having been reported from Taiwan (see Li and Wang 1995; Shen and Wu 2011). Comparative specimens were collected from relatively deep water (80–101 m). The Japanese specimens were collected from Nakagusuku Bay (26°15′N, 127°49′E), east coast of Okinawa Island, from 17–41 m depth, during experimental bottom-trawling surveys.

Status of type specimens. Pseudorhombus quinquocellatus was originally described by Weber and de Beaufort (1929), based on three syntype specimens from Madura Strait (between Madura Island and Java) and the Kange- an Islands, Indonesia. Two of the syntypes (from Madura Strait) are currently held at Nationaal Natuurhistorisch Museum, Leiden (now Naturalis Biodiversity Center) ( Fig. 6C, D ), and one of them (ZMA.PISC.112569) has been deemed to be designated by Norman (1934) as the lectotype of P. quinquocellatus (ZMA.PISC.109328 thus becoming a paralectotype), according to Nijssen et al. (1982: 107; 1993: 234), in their comprehensive fish type catalog for ZMA. However, in his account of P. quinquocellatus, Norman (1934: 100) treated the two syntypes as “co-types” and did not explicitly designate a lectotype for the species (see Article 74.5 of the International Code of Zoological Nomenclature; International Commission on Zoological Nomenclature 1999). Despite a hand-written label associated with ZMA.PISC.112569 referring to the specimen as “type”, with a second referring to ZMA.PISC.109328 as “cotype”, we consider that the two ZMA specimens, in addition to the third specimen, of which location remains unknown, should be considered as syntypes of P. quinquocellatus for the time being.

Remarks. Following the key to species of Pseudorhombus in Amaoka and Hensley (2001), the present non-type specimens were identified as P. quinquocellatus , characterized by the following combination of characters: 69–73 dorsal-fin rays, 53–55 anal-fin rays, ocular-side body with two pairs of ocelli above and below lateral line and a single ocellus on the posterior portion of the lateral line (total five ocelli), gill rakers long and pointed ( Fig. 3C ), ocular-side body covered with ctenoid scales, blind-side body covered with cycloid scales, anterior dorsal-fin rays not elongated, first dorsal-fin ray base situated above blind-side anterior nostril, dorsal-fin origin in front of upper eye (ocular-side view), and strong canine teeth on both jaws ( Fig. 2C ).

Excepting P. oculocirris and P. pentophthalmus , P. quinquocellatus is readily distinguished from all Japanese congeners by having five obvious ocellated spots on the ocular side of the body, compared with two or three blotches along the lateral line in P.arsius , P. cinnamoneus , P. elevatus , P.oligodon and P. levisquamis ( Fig. 5A–E ), and usually three double ocelli in P. dupliciocellatus ( Fig. 5I ). Moreover, P. quinquocellatus can be readily distinguished from P. oculocirris and P. pentophthalmus by having 2–8 strong canine teeth on the anterior portions of both jaws (vs. numerous small conical teeth in both of the latter), fewer lower gill rakers on the ocular side (9–11 in P. quinquocellatus vs. 16–21 in P. oculocirris and 15–18 in P. pentophthalmus ), and two large dark flaps along the gill opening below the pectoral-fin base ( Figs 6B , 7 ) (vs. skin fold variously shaped, not forming two flaps) (this study). Pseudorhombus oligodon also possesses two dark flaps along the gill opening ( Fig. 5E ; see Amaoka and Hensley 2001), but differs from P. quinquocellatus in having ctenoid scales on the blind-side of the body (vs. cycloid in the latter).

Standard Japanese name. Kyushin et al. (1973) initially recorded P. quinquocellatus from the Andaman Sea on the basis of a single specimen (catalog number not provided), and subsequently Kyushin et al. (1977) noted the same specimen (as P. quinquocellatus ), with a newly proposed standard Japanese name “Itsutsume-ganzō” for the species. That specimen (HUMZ 90027, 203.8 mm SL, Andaman Sea; Fig. 6E ) was herein identified as P. megalops , having a characteristic black spot on the ocular-side pelvic fin ( Fig. 6F ) and the following other diagnostic characteristics defined by Hensley and Amaoka (1989) for the species, viz., 70 dorsal-fin rays, 74 pored lateral-line scales, gill rakers elongated, 13 rakers on the lower limb, both jaws with large canines, lower jaw with ca. 14 teeth on blind side, ocular-side body covered with ctenoid scales, blind-side body covered with ctenoid scales near dorsal- and anal-fin bases, other areas with weakly ctenoid scales. In addition to the pelvic-fin spot, P. megalops is readily distinguished from P. quinquocellatus in having many dark rings (not ocelli) on the ocular-side body (vs. five distinct ocelli in the latter) and a higher number of lower gill rakers 13–18 (vs. 9–11) ( Hensley and Amaoka 1989; this study). We consider that the Japanese name “Itsutsume-ganzō” should be applied to P. megalops , even though the species does not occur in Japanese waters.

Therefore, the standard Japanese name “Niten-ganzō-birame” is newly proposed for P. quinquocellatus , based on KAUM–I. 55592, being derived from the characteristic two dark flaps along the gill opening (“niten” = two spots; “ganzō-birame” = Japanese common name of Pseudorhombus ).

Figures

Fig. 1. Preserved (A, B, D) and fresh (C) specimens of Pseudorhombus elevatus. A, KAUM–I. 55230, 118.4mm SL, Okinawa Island, Japan; B, KAUM–I. 55656, 39.0mm SL, Okinawa Island, Japan; C, KAUM–I. 105148, 110.5mm SL, Terengganu, Malaysia; D, QM I.1569, holotype of P.elevatus, 120.5mm SL, Queensland, Australia (photo by J. Johnson).

Fig. 2. Ocular-side teeth of Pseudorhombus elevatus (A, B) and P. quinquocellatus (C) from Okinawa Island, Japan (B, C: schematic drawings). A, KAUM–I. 55230, 118.4mm SL; B, KAUM–I. 55641, 41.1mm SL; C, KAUM–I.55592, 46.3mm SL. Bars indicate 2mm.

Fig. 3. Ocular-side first gill arches of Pseudorhombus elevatus (A, B) and P. quinquocellatus (C, D). A, KAUM–I. 55641, 41.1mm SL, Okinawa Island, Japan; B, KAUM–I. 55235, 135.7mm SL, Okinawa Island, Japan; C, KAUM–I. 55592, 46.3mm SL, Okinawa Island, Japan; D, ZMA.PISC.112569, syntype of P. quinquocellatus, 150.1mm SL, Madura Strait, Indonesia. A and C, alizarin red stained.

Fig. 4. Dorsal-fin origin (D), anterior (AN) and posterior (PN) nostrils on blind side of Pseudorhombus elevatus (A, B) and P. quinquocellatus (C) from Okinawa Island, Japan (B, C: schematic drawings). A, KAUM–I. 55230, 118.4mm SL; B, KAUM–I. 55641, 41.1mm SL; C, OCF-P 10720, 55.5mm SL. Bars indicate 2mm.

Fig. 5. Schematic drawings of Japanese species of Pseudorhombus, including P.elevatus (A), P.arsius (B), P.cinnamoneus (C), P. levisquamis (D), P. oligodon (E), P. quinquocellatus (F), P. oculocirris (G), P. pentophthalmus (H), and P. dupliciocellatus (I), showing obvious markings and dark skin flaps along gill opening on ocular side. Based on: A, KAUM–I. 105148, 110.5mm SL; B, KAUM–I. 169146, 327.0mm SL; C, KAUM–I. 88590, 232.8mm SL; D, KAUM–I. 42865, 341.4mm SL; E, KAUM–I. 160254, 238.4mm SL; F, KAUM–I. 113356, 121.7mm SL and ZMA.PISC.109328, 153.5mm SL; G, KAUM–I. 115224, 173.6mm SL; H, KAUM–I.75596, 136.6mm SL; I, KAUM–I. 109946, 295.6mm SL.

Fig. 6. Specimens of Pseudorhombus quinquocellatus (A–D) and P. megalops (E, F) in preserved (A, C–F) and fresh (B) conditions. Magnification of ocular-side pelvic fin of P.megalops (F), showing single dark blotch on 4th ray (indicated by arrow). A, KAUM–I. 55592, 46.3mm SL, Okinawa Island, Japan; B, KAUM–I. 113356, 121.7mm SL, Pingtung, Taiwan; C, ZMA.PISC.112569, syntype of P. quinquocellatus, 150.1mm SL, Madura Strait, Indonesia; D, ZMA.PISC.109328, syntype of P. quinquocellatus, 153.5mm SL, Madura Strait, Indonesia; E, F, HUMZ 90027, 203.8mm SL, Andaman Sea.

Fig. 7. Head of preserved specimen of Pseudorhombus quinquocellatus, showing skin flaps (arrows) along gill opening. KAUM–I. 55592, 46.3mm SL, Okinawa Island, Japan.