Crossorhombus howensis Hensley & Randall, 1993

Amaoka, Kunio & Ho, Hsuan-Ching, 2019, The lefteye flounder family Bothidae (Order Pleuronectiformes) of Taiwan, Zootaxa 4702 (1), pp. 155-215 : 178-180

Crossorhombus howensis Hensley & Randall, 1993

Lord Howe Island flounder; ȑẋḃľ

Figures 5 E–H; Table 6

Crossorhombus howensis Hensley & Randall, 1993:1120 (Type locality: Lord Howe Island). Shen & Wu, 2012:750.

Specimens examined. USNM 260394 (1 male, 103; 1 female, 60.0), paratypes, cut between large outstanding rock and Ch'uan-fan-shih, Hengchun , Pingtung, 0–6 m , 23 Apr. 1968.

Diagnostic features. D 87–88; A 67–69; P 11–12; C 2+13+2=17; LLs 53–54; GR 0+6=6; vert. 10+25=35.

Body short and deeply ovate, greatest depth slightly before middle part of body (59.4% SL). Head much shorter than half of body depth (23.1–23.9% SL); upper profile of head with deep concavity anterior of upper margin of lower eye; head profile steep, nearly vertical in mature males, less steep in females and juveniles. Snout much shorter than eye diameter. Rostral spine on tip of snout, sharp and strong in males, absent in females and juveniles. Eye diameter slightly shorter than upper-jaw length. Small orbital spines at anterior margins of either eyes in males, (absent in females and juveniles); flaps on posterior area of eyes in male. Interorbital space deeply and widely concave, wider in males than females and juveniles.

Mouth small and lipped, upper-jaw length 6.2–6.9% SL; maxilla extending to anterior margin of lower eye. Teeth on upper jaw biserial, those on outer series larger and more widely spaced than those on inner series; teeth on lower jaw uniserial, similar to inner teeth of upper jaw. Gill rakers on lower limb short and blunt, not serrate; absent on upper limb. Scales on ocular side small, ctenoid with long ctenii on posterior margin; scales on blind side cycloid. Pectoral-fin rays on ocular side about as long as head in males (27.8–31.8% SL) and shorter than head in females (ca. 20% SL).

Coloration. Ocular side of body yellowish brown with many dark spots and obtuse dark specks; a series of dark spots along dorsal and ventral margins of body; 4–5 spots along straight section of lateral line; dorsal, anal and caudal fins light with small dark specks; flaps on eyes with dark spots; blind side of body in males with distinct deep-bluish pattern in horizontal V-shape, uniformly whitish in female.

Size. Reaching 103 mm SL in Taiwan; up to 107 mm SL in Lord Howe Island ( Hensley & Randall, 1993).

Distribution. Southern Taiwan off Hengchun, Pingtung; Lord Howe Island ( Hensley and Randall, 1993).

Remarks. This species exhibits a distinct, sexual dimorphism in respect to the interorbital width, presence of rostral and orbital spines, flaps on eyes (rarely on one eye), pectoral-fin length on ocular side and body coloration on the blind side. Crossorhombus howensis closely resembles C. valderostratus in having a deep-bluish horizontal V-shaped pattern in males, but differs from latter in having a shorter pectoral fin on the ocular side in males (27.8– 31.8% SL, vs. 32.6–41.9), and a caudal fin without any dark band at posterior margin. Two male paratypes were collected from Taiwan, but we were unable to obtain any further specimens. This species may be rare in Taiwan.

Figures

FIGURE 5. A–D. Crossorhombus azureus, NMMB-P22299, male, 113.3 mm SL (A–B) and female, 94.7 mm SL (C–D). E–H. C. howensis, USNM 260394, male, 103.0 mm SL (E–F) and female, 62.0 mm SL (G–H).