Arnoglossus macrolophus Alcock 1889

Arnoglossus macrolophus Alcock, 1889

Largecrested lefteye flounder; łī¥6ľ

Figure 1C; Tables 1–2

Arnoglossus macrolophus Alcock, 1889:280, pl. 18, fig. 2 (Type locality: south of Ganjam, Bay of Bengal). Arai & Amaoka, 1996:359; Shen & Wu, 2012:747.

Arnoglossus tapeinosoma: Shen in Shen et al., 1993:567; Shen & Wu, 2012:748.

Specimens examined. NMMB-P1786 (1 male, 59.8), Daxi, 9 Sep. 2003; NMMB-P8215 (1 female, 87.5), Donggang, 16 Jun. 2004; NMMB-P23204 (1 male, 81.1), Ke-tzu-liao, 31 Mar. 2016; NMMB-P29430 (1 male, 74.2), Ke-tzu-liao, 24 Apr. 2018

Diagnostic features. D 89–94; A 69–74; P 13–14; C 2+13+2=17; LLs 52–57; GR 0+10–12=10–12; vert. 10+30–32=40–42.

Body elliptical, greatest depth at about middle part of body (37.3–41.4% SL). Head small, its length about half of body depth (23.3–25.1% SL); front profile of head with slight concavity anterior of upper eye; head profile gentle, same in both sexes. Snout slightly shorter than eye diameter. Rostral spine absent on tip of snout in both sexes. Eye diameters distinctly shorter than upper jaw. No orbital spines in both sexes. Interorbital ridge low, extending from anterior margin of lower eye to posterior margin of upper eye.

Mouth moderately large, upper-jaw length on ocular side 8.8–10.1% SL; maxilla extending to or slightly behind anterior margin of lower eye; teeth on both jaws uniserial, closely set, without enlarged anterior teeth. Gill rakers only on lower limb of first arch, slender, pointed at tip and not serrate.

Scales on ocular side ctenoid with row of slender ctenii, cycloid on blind side. Anteriormost four to six dorsalfin rays slender, filamentous, first ray longest, 32.9–64% SL in males, 28.7% SL in females. Pectoral fin on ocularside shorter than head, 11–16% SL; that on blind-side small.

Coloration. Ocular side of body uniformly pale brownish, a dark blotch at junction of straight and curved portions of lateral line, two small blotches on middle of straight portion of lateral line; a series of five dark obscure blotches along dorsal margin and three along ventral margin of body; posterior parts of dorsal and anal fins with conspicuous black blotches basally. Blind side of body yellowish white.

Size. Reaching 88 mm SL in Taiwan; up to 130 mm total length elsewhere (Hensley & Amaoka, 2001).

Distribution. Northeastern and southwestern Taiwan; Indian and Western Pacific ocaens (Amaoka, 2016).

Remarks. This species is easily separated from other species of this genus in having four to six filamentous anteriormost rays of dorsal fin in males and a distinct blotch on the posterior parts of the dorsal and anal fins, respectively. The sexual dimorphism occurs in specimens larger than about 55 mm SL.