Asterorhombus cocosensis ( Bleeker, 1855 )

Amaoka, Kunio & Ho, Hsuan-Ching, 2019, The lefteye flounder family Bothidae (Order Pleuronectiformes) of Taiwan, Zootaxa 4702 (1), pp. 155-215 : 166-167

Asterorhombus cocosensis ( Bleeker, 1855)

Angler flatfish, Cocos Island flounder; ªª¥6ľ

Figures 2 A–B; Table 3

Rhombus cocosensis Bleeker, 1855:179 (Type locality: Cocos Island, Australia).

Engyprosopon fijiensis Norman, 1931a:508 (Type locality: Fiji Islands)

Asterorhombus fijiensis: Hensley, 1986:941 ; Lin et al., 1995:26.

Asterorhombus cocosensis: Hensley, 2003:833 ; Shen & Wu, 2012:748.

Specimens examined. ASIZP 57101 (1 female, 98.1), Taiping Island ( Itu Aba Island ), South China Sea, 20 Apr. 1994 . Other localities: RMNH 6730 (holotype of Rhombus cocosensis , 71.7), Cocos Island , Indian Ocean ; BMNH 1879.5 .14.89, (holotype of Engyprosopon fijiensis , 68.1), Levuka , Fiji, 8 Aug. 1983 ; WAM P 28028-013 (1 female, 62.5), Rowley Shoals , Cleeke Reef, Bedwell Island, 8 Aug. 1982 ; IOP 3303 (1 male, 109.9), Kerama Islands , Okinawa Prefecture, Japan, 21 Mar. 21 , 1993.

Diagnostic features. D 82 (79–82 from other localities); A 62 (59–62); P 11 (11–13); C 2+13+2=17; LLs 55 (52–58); GR 0+9 (0+8–9); vert. 10+26=36 (10+25–26=35–36).

Body ovate, greatest depth at middle part of body 55.1 (53.3–54.1)% SL. Head longer than half of body depth 28.8 (27.9–30.2)% SL; upper profile of head with slight concavity in front of upper margin of lower eye; head profile relatively steep. Snout long, its length less than 1/3 HL. Eyes small, separated by deep and wide space, their width slightly wider in males than in females and juveniles; surface of upper eye rarely with 1–9 tentacles.

Mouth large, curved; upper-jaw length 11.5 (11.2–12.2)% SL; maxilla extending to anterior margin of lower eye; posterior half of ventral margin of lower jaw with some membranous flaps. Teeth on both jaws uniserial, upper jaw teeth small and short, somewhat enlarged anteriorly, smaller and more closely set posteriorly; teeth on lower jaw similar to anterior teeth on upper jaw. Gill rakers only on lower limb, short and palmate with 2–5 spines.

Scales on ocular side rather small, ctenoid with short ctenii; cycloid scales on blind side; snout, both jaws, pectoral fin and pelvic fin scaleless. First dorsal-fin ray elongate, separated from remaining rays, with large leaf-like membrane at tip; fin membranes of anterior second to fourth rays deeply incised. Pectoral-fin short on ocular side, a little longer than half of HL 15.8 (15–16.2)% SL.

Coloration. Ocular side of body uniformly yellowish brown, with many obtuse ocelli, larger than eye, and numerous small dark spots; all fins with many small dark spots except for pectoral fin; body, fins and membranous tip of first dorsal ray with red blotches in fresh specimens.

Size. Reaching 98.1 mm SL in Taiwan; up to 150 mm TL elsewhere ( Hensley & Amaoka, 2001).

Distribution. The only record for Taiwan is from Taiping Island (Itu Aba Island), South China Sea; widespread in the Indian and Western Pacific oceans ( Amaoka, 2016).

Remarks. Lin et al. (1995) identified the same specimen examined herein as Asterorhombus fijiensis , which is a junior synonym of A. cocosensis . This species has a lure originated from the first dorsal-fin ray, which resembles a small crustacean in form and coloration. Divers observed the lure to repeatedly vibrate ( Amaoka et al., 1994).

Figures

FIGURE 2. A–B. Asterorhombus cocosensis, ASIZP 57101, female, 98.1 mm SL fresh, photo by J.-P Chen (A), preserved (B). C–D. A. intermedius, ASIZP 57100, male, 87.7 mm SL, photo by J.-P Chen (C), underwater photo taken from Lang-dao, Orchid Island, photo by J.-P. Chen (D).

Tables

TABLE 3. Frequency of six meristic data of two Asterorhombus species; * indicates the value of specimens (one in each species) collected from Taiwan.

			Dorsal-fin rays										Anal-fin rays
	n	79	80	81	82	83	84	85		n	58	59	60	61	62	63	64	65
A. cocosensis A. intermedius	5 33	1	0 2	1 2	3* 9	14*	3	3		5 34	1	1 0	0 0	2 4	2* 12	9*	6	2
				Lateral-line scales										Pectoral-fin rays
	n	50	51	52	53	54	55	56	57	58		n	10	11	12	13
A. cocosensis A. intermedius	5 31	2	4	1 5	0 8	2 2	1* 5*	0 3	0 2	1		5 33	7*	3* 24	1 2	1
		Gill rakers (upper + lower)									Vertebrae (precaudal + caudal)
	n	0	+	8	9	10	11		n	10	+	25	26	27	28
A. cocosensis A. intermedius	5 33	5* 33*		3 13*	2* 15	4	1		5 31	5* 31*		1	4* 2	26	3*