Chascanopsetta prognatha Norman, 1939

Amaoka, Kunio & Ho, Hsuan-Ching, 2019, The lefteye flounder family Bothidae (Order Pleuronectiformes) of Taiwan, Zootaxa 4702 (1), pp. 155-215 : 174-177

Chascanopsetta prognatha Norman, 1939

Longchin pelican flounder; ñłāľ

Figures 4B, C ; Table 5

Chascanopsetta prognathus Norman, 1939:100 (Type locality: Maldives).

Chascanopsetts normani Kuronuma, 1940:40 (Type locality: Suruga Bay, Japan)

Chascanopsetta prognatha: Hensley & Smale, 1998:13

Specimens examined. NMMB-P30849 (8, 132.5–313.2) , HUMZ 230193 – 230195 (3, 198.8–218.0), Dong-sha Is- lands (Pratas Islands), bottom trawl, ca. 300–400 m , 13 Feb. 2019.

Diagnostic features. D 121–135; A 82–93; P 14–17; C 2+13+2=17; LLs 176–208; GR 0+0–3; vert. 17–18+42– 44=59–61.

Body elongate elliptical, rather soft and flabby; greatest depth 23.0–29.1% SL, at posterior margin of abdominal cavity. Caudal peduncle narrow, its depth about 4.0–5.7%SL of body depth. Head relatively small (18.4–21.6% SL); upper profile of head with slight concavity anterior of dorsal margin of lower eye. Snout blunt and short, its length about 2/3 of eye diameter. Eyes separated by narrow flat space, its width about 1/3 to 1/4 of eye diameter.

Mouth extremely large, upper-jaw length 16.7–20.3% SL (14.4% in young, 132.5 mm SL); maxilla extending far beyond posterior margin of lower eye; tip of lower jaw reaching much beyond tip of upper jaw, projecting length about equal to 1/5 of the whole length. Teeth on both jaws uniserial, slender, curved inward and depressible; teeth on lower jaw stronger than those on upper jaw. Gill rakers on lower limb, rudimentary, none on upper limb. Scales on both sides very small and deciduous, cycloid. Some anterior rays of dorsal fin slightly elongated, free from fin membrane except for base. First ray of anal fin connected with last ray of pelvic fin by narrow membrane. Pectoral fin on both sides slender, its length on ocular side about 11.5–16.6% SL. Caudal fin slender, rather long and with rounded tip.

Coloration. Ocular side of body uniformly pale brownish or pale grayish without markings; peritoneum dark blue with narrow pale brownish bands; median fins and paired fins dusky, anterior dorsal-fin rays more or less pale. Blind side of body light brownish except for light blue peritoneum.

Size. Reaching 313.2 mm SL in Taiwan, also the largest known specimen.

Distribution. Dongsha Island, South China Sea; Indian to Western Pacific oceans.

Remarks. This species has been confused with Chascanopsetta lugubris . However, they are easily separable by the characters shown in the key of species. Ho et al. (2009) listed 10 specimens of C. prognatha (NMMB-P1985) which have been misidentified as C. lugubris . The presence of C. prognatha in Taiwan is confirmed based on specimens newly collected from Dongsha Island, South China Sea.

Figures

FIGURE 4. A. Chascanopsetta lugubris, NMMB-P25745, 296.4 mm SL. B–C. C. prognatha, NMMB-P30849, 198 mm SL, fresh (B) and preserved (C).

Tables

TABLE 5. Frequency of six metirtic data of two Chascanopsetta species in Taiwan.

Dorsal-fin rays
	n	115	116	117	118	119	120	121	122	123	124	125	126	127	128	129	130	131	132	133	134	135
C. lugubris C. prognatha	19 16	1	2	1	1	3	4	3 1	0 0	1 0	3 2	3	2	2	2	1	1	0	0	1	0	1
														Anal-fin rays
	n	78	79	80	81	82	83	84	85	86	87	88	89	90	91	92	93
C. lugubris C. prognatha	20 16	2	1	1	2	2 1	4 0	4 0	3 1	1 3	1	0	4	2	2	0	2
Lateral-line scales
	n	157	158	159	160	161	162	163	164	165	166	167	168	169	170	171	172	173	174	175	176	177	178	179	180	181	182
C. lugubris C. prognatha	20 16	2 183 0 0	0 184 1 0	0 185 1 1	1 186 2 1	1 187 0 0	0 188 0 1	0 189 0 0	1 190 1 1	0 191 1 0	1 192 1 1	0 193 0 0	0 194 0 1	0 195 0 1	0 196 0 1	0 197 1 0	1 198 0	1 199 0	0 200 0	1 201 0	0 1 202 1	0 0 203 0	1 2 204 1	0 1 205 0	1 0 206 0	1 0 207 0	0 1 208 1
			Pectoral-fin rays							Gill rakers (upper+lower)										Vertebrae (precaudal+caudal)
	n	14	15	16	17				n	0	+	0	1	2	3		n	17	18	+	38	39	40	41	42	43	44
C. lugubris C. prognatha	20 16	5 4	11 6	3 4	1 2				16 16	16 16		4	1 3	3 4	12 5		21 4	21 3	1		7	12	2		2	1	1