Engyprosopon mogkii

Engyprosopon mogkii (Bleeker, 1854)

Figures 6–7; Table 1

Rhombus mogkii Bleeker, 1854:256 (type locality: Manado, Sulawesi, Indonesia). Rhomboichthys (Engyprosopon) mogkii: Günther, 1862:438.

Pseudorhombus mogkii: Bleeker, 1863:230.

Platophrys (Arnoglossus) mogkii: Bleeker, 1870 -75:14.

Engyprosopon mogkii: Weber, 1913:429; Norman, 1927:27; Norman, 1934:207. Bothus (Arnoglossus) mogkii: Weber & Beaufort, 1929:129.

Material examined. ASIZP 63578, male, 91.1 mm SL, Daxi, Yilan, northeastern Taiwan, 29 Sep. 2000; NMMB- P11510, male, 63.0 mm SL, Dapong Bay, Pingtung, southwestern Taiwan, 18 Sep. 1999.

Diagnosis. No concavity on head margin anterior to lower eye (Fig. 6A); gill rakers very slender, long and not serrate (Fig. 7B); narrow interorbital width; no sexual dimorphism in coloration on blind side of body (Fig. 6B).

Description. Dorsal-fin rays 85–87, anal-fin rays 63–67, ocular-side pectoral-fin rays 11–12, blind-side pectoral-fin rays 8–9, caudal-fin rays 3 + 11 + 3, ocular-side pelvic-fin rays 6, blind-side pelvic-fin rays 6, scales in lateral line 50–51, gill rakers 0 + 6–8, vertebrae 10 + 24–25.

In SL: HL 3.75–4.05, body depth 1.82–1.89. In HL: snout 4.17–5.79, upper eye diameter 3.65–4.09, lower eye diameter 3.65–4.17, interorbital width 7.81–12.5, ocular-side upper jaw 2.74–3.01, blind-side upper jaw 2.65–2.90, ocular-side lower jaw 2.14–2.19, blind-side lower jaw 1.99–2.05, caudal peduncle depth 1.74–2.23, ocular-side pectoral fin 1.17–1.23, blind-side pectoral fin 1.76–1.93, ocular-side pelvic fin 2.18–2.81, blind-side pelvic fin 2.03–2.27, base of ocular-side pelvic fin 2.47–2.58, base of blind-side pelvic fin 7.76–8.40, longest dorsal fin ray 1.84–2.06, longest anal fin ray 1.92–1.98, middle caudal fin ray 1.07–1.24.

Body ovate, deepest slightly anterior to vertical through middle of body; body depth about 1/2 of SL; dorsal and ventral contours gently arched, anterior half of dorsal contour of body slightly steeper than contour of posterior half. Caudal peduncle moderately deep, its depth less than 1/3 of body depth. Head small, its length about 1/4 of SL; upper head profile without concavity anterior to lower eye. Snout short, shorter than eye diameter. Rudimental rostral spine present in males (absent in females and juveniles in comparative specimens). Eyes small, both diameters less than length of maxilla; lower eye slightly in advance of upper eye. No orbital spine in either sex. Interorbital area distinctly concave (no sexual and ontogenetic differences noted). Nostrils on ocular side anterior to upper margin of lower eye; anterior nostril a short tube with a small triangular flap posteriorly; nostrils on blind side closely set below origin of dorsal fin, similar in shape to those on ocular side.

Mouth rather large, oblique; maxilla extending ventroposteriorly to slightly beyond anterior margin of lower eye; anterior tips of both jaws nearly on same vertical line when mouth closed. Small symphysial knob at ventral tip of mandible. Teeth on upper jaw biserial, those in outer series larger and more widely spaced than those in inner series; lower jaw teeth uniserial, conical, all teeth almost the same size. Gill rakers on first arch slender, with sharp tips, inside edge smooth; no gill rakers on upper limb; borders between each gill lamella, except those on distal of lower limb and those basal to distal half of upper limb, with dark pigmentation (Fig. 7B).

Ocular-side scales small, ctenoid with short ctenii (Fig. 7A); tips of both jaws and ocular side of snout naked; scales on blind side of body cycloid. First dorsal fin ray with anterior and posterior flaps somewhat free from other rays; second to sixth dorsal-fin rays more or less elongate (based on comparative specimens). Second pectoral fin ray on ocular-side elongate in males, short in females and juveniles. Ocular-side pelvic-fin origin at tip of isthmus, ocular-side fifth pelvic-fin ray opposite to first ray of blind-side pelvic fin. Tip of isthmus near vertical line through middle of lower eye. Caudal-fin rays branched, except for three upper- and three lowermost rays.

Coloration in alcohol. Ocular side of body dark brown with many darker and paler spots; a series of dark spots on straight part of lateral line. Blind side of body pale yellowish-white in both sexes. All fins on ocular side fins dark brown with numerous dark spots; paired fins on blind side uniformly yellowish white.

Sexual dimorphism. This species shows sexual dimorphism only in length of the ocular-side pectoral fin and in the presence of a rostral spine on the snout.

Distribution. Widespread in the Indo-West Pacific Ocean: Taiwan, Malay Peninsula and Archipelago and Coral Sea, through the Indian Ocean. Bathymetric range 2–198 m (Hensley & Amaoka, 2001).

Remarks. This species clearly differs from most congeners in not having secondary sexual differences in the width of the interorbital space, in the rostral spine (obscure spine in large males), and in the coloration of the blind side of the body. This species is closely related to species of the genus Asterorhombus in the absence distinct sexually dimorphic characters and by the distinct branching features in the caudal skeleton (Amaoka & Arai, 1998). Despite similarities in these features, this species belongs in Engyprosopon, as Asterorhombus is welldefined by having a lure on the first dorsal-fin ray and palmate gill rakers (Hensley, 2005). The present study is the first record of this species from off Taiwan, and is also the northernmost and easternmost records for this species.