Squatina japonica (Bleeker, 1858)

Jonathan H. Walsh & David A. Ebert, 2007, A review of the systematics of western North Pacific angel sharks, genus Squatina, with redescriptions of Squatina formosa, S. japonica, and S. nebulosa (Chondrichthyes: Squatiniformes, Squatinidae)., Zootaxa 1551, pp. 31-47 : 40-42

Squatina japonica (Bleeker, 1858)

Squatina japonica, Bleeker 1858 : 40, valid, holotype (unique): RMNH 7416 (Eschmeyer, 2005). Figure 4.

Common name. Japanese angel shark.

Diagnosis. A list of the following distinctive characters: wide but shallow upper lip arch (4.2-5.0% TL in width, 0.8-1.1% TL in height); spiracles with numerous large papillae on inside anterior edge, papillae boxlike in shape; row of thorny tubercles on dorsal originating mid-back and extending to the caudal peduncle; pelvic fins not reaching origin of first dorsal; dorsal fins angular in shape, dorsal bases roughly equal; rusty brown coloration above with fine spotting pattern of numerous small square-shaped spots throughout.

Description. Dorsal surface, except for posterior portion of caudal fin, covered with denticles of moderate roughness. Row of tubercles extending posterior from mid-back, also present interdorsal and dorsal-caudal space but smaller in size. Ventral surface smooth except for narrow bands of denticles on the pectoral and pelvic fins.

Head somewhat diamond in shape dorsally, length about 0.2 times total length, greatest width occurring just anterior of first gill opening. Interspersed moderately rough tubercles above mouth and eye crests. Eyes almond-shaped, widely set, interorbital space (9.1; 8.8-9.5). Eye-spiracle space short. Interspiracle space (10.0; 9.7-10.3) slightly greater than interorbital space. Spiracles crescent shaped with large box-like papillae on inside anterior margin. Center of upper lip exposed forming a broad narrow arch, extends nearly one half the height of upper lip space, upper lip arch height (0.9; 0.8-1.1), upper lip arch width (4.7; 4.2-5.0). Labial furrows conspicuous, extending from corners of mouth medially. Upper furrows partially concealed with dermal skin lobes. Upper labial furrows about 1.2 times longer than lower labial furrows. Small nasal flaps protruding from dermal folds above mouth with two barbels protruding from each flap. Inner nasal barbel spatulate with inner basal portion containing little if any fringe. Outer nasal barbel narrow. Nostrils large and slightly protruding. Slight lobes present at corners of mouth extending ventrally. Mouth length about 0.2 times as long as mouth width. Dentition consisting of small, dagger-like teeth, conical without cusplets on a broad base, in 3 orderly longitudinal rows, no teeth at symphysis, teeth by row 10 - 10 / 10 - 10.

Pectoral fins large, somewhat rounded posteriorly, originating just behind gills. Anterior margin of pectoral fin, slightly curvilinear, about equal to pectoral fin length, extending to lateral apex. Angle of lateral apex slightly more obtuse than 90°. Margin from lateral apex to most posterior lobe straight to slightly concave. Posterior lobe moderately convex. Pectoral inner margin broadly convex.

Pelvic fins, originating anterior to pectoral posterior free tip, somewhat triangular with rounded fintips. Anterior margin, slightly convex, approximately 0.6 times as long as pelvic fin length, extends at roughly a 45° angle from trunk to broadly rounded lateral apex. Pelvic girdle width (33.1; 32.1-34.5) very broad. Posterior margin of pelvic fin straight to posterior free tips which do not reach origin of first dorsal. Pelvic inner margin straight to insertion of pelvic fin.

Dorsal fins lobe-like and about identical in size, with denticles extending over the whole of the fins. Interdorsal space about 0.9 times as long as dorsal caudal finspace. Anterior margins of dorsals convex, nearly equidistant. Dorsal bases nearly equal, first dorsal base (3.0; 2.8-3.2), second dorsal base (3.0; 2.7-3.2). Apex of dorsals lobed. Posterior margins slightly convex, about 0.6 times as long as anterior margins. Inner margins of dorsals slightly convex, approximately 0.4 times as long as anterior margins.

Caudal peduncle compressed dorso-ventrally with large lateral longitudinal ridges, tapering posteriorly.

Caudal fin angular throughout, especially dorsally. Caudal dorsal margin about 0.8 times as long as caudal preventral margin. Dorsal lobe somewhat triangular with rounded apex. Subterminal caudal fin margin present in all but one specimen, approximately 0.4 times as long as upper postventral caudal margin. Lower caudal postventral margin straight to slightly convex, about 0.9 times as long as upper caudal postventral margin.

Coloration. Dorsal surface of specimens prior to preservation light to dark brown throughout with a distinct freckled pattern of numerous square-shaped black spots. Spots slightly smaller on edges of trunk and fins, absent on dorsals above base and caudal outside of caudal vertebral column. Larger black splotches laterally at origins of dorsals. Ventral surface pale white with some black mottling, pectoral and pelvic fin ventral margins with denticles colored similar to dorsal. After preservation color tends to fade to a lighter brown, spotting pattern can also fade to blend in with overall color.

Distribution. Endemic to the WNP including the Sea of Japan, along the south eastern Japan coast, Yellow Sea, East China Sea, waters surrounding northern Taiwan, and the Taiwan Strait (Shuyuan, 1994; Randall & Lim, 2000; Compagno et al., 2005a).

Etymology. Naming is in allusion to where the holotype was described (Japan).

Remarks. Squatina japonica is the only WNP species in this study to possess mid-back thorns. Compagno, 1984 illustrates S. nebulosa as possessing midback thorns, but we did not observe these in any of the specimens we examined. Midback thorns are also not present on the holotypes of S. formosa or S. nebulosa , and photographs and illustrations of S. tergocellatoides specimens.

Literature descriptions (Lindberg & Legeza, 1967) indicate that interspiracle distance is greater than interorbital distance in S. japonica ; a finding consistent with our observations.

Material Examined. HUMZ 107395, immature female, off Shirahama, Shimoda City, Shizuoka prefecture, Japan, 27 Jan 1986, caught with a bottom gill net at 30 m ; HUMZ 105913 immature male, off Itado, Shimoda, Shizuoka prefecture, Japan, 19 Nov 1985, caught with a bottom gill net at 10m ; CAS 20955: immature male, Japan, Tokyo Market, collected by R/V Snyder and Sindo as part of the “Albatross 1906 cruise ; ” CAS 20956, immature male, Japan, Tokyo market, collected by R/V Snyder and Sindo as part of the “Albatross 1906 cruise.”