Polysteganus flavodorsalis, Iwatsuki, Yukio & Heemstra, Phillip C., 2015

Iwatsuki, Yukio & Heemstra, Phillip C., 2015, Redescriptions of Polysteganus coeruleopunctatus (Klunzinger 1870) and P. lineopunctatus (Boulenger 1903), with two new species from Western Indian Ocean, Zootaxa 4059 (1), pp. 133-150 : 141-144

Polysteganus flavodorsalis new species

Proposed English name: Yellowfin Seabream Figure 3 A–C; Table 2

Holotype. SAIAB 84079, 143 mm SL (X), sex not determined, Nazareth Bank, Mascarene Plateau (11.15°41.11'S, 61°04.54'E), Trawl No. Mascarene-7, depth 302‒305 m, coll. by D. Tweddle & O. Alvheim, 18 October 2008.

Paratypes. SAIAB 84022, 3 specimens, 247−265 mm SL (X), sex determined only for 265 mm SL specimen examined, off Cargados Carajos, Mascarene Plateau, Trawl No. Mascarene-7 (16°27.62'S, 60°16.84'E), coll. by D. Tweddle & O. Alvheim, depth 214 ‒ 219 m, 14 October 2008; SAIAB 84072, 223 mm SL (X), Nazareth Bank, Mascarene Plateau, Trawl No. Mascarene-10 (15°55.43'S, 60°13.38'E), depth 232 ‒ 236 mm (X), coll. and photographed by D. Tweddle & O. Alvheim; SAIAB 84097, 218 mm SL (X), Nazareth Bank, Mascarene Plateau, Trawl No. Mascarene-12 (15°23.32'S, 61°13.41'E), coll. by D. Tweddle & O. Alvheim, depth 258 ‒ 288 m, 19 October 2008.

Diagnosis. Distinguished from all congeners of Polysteganus by the following combination of characters: scale rows above lateral line 6½; scales rows between 5th dorsal-fin spine base and lateral line 5½; pored lateralline scales 52 or 53; suborbital depth clearly less than orbit diameter (OD), 72–75% (mean 74%) of OD; dorsal-fin rays reddish pink with bright yellow margin, anal-fin rays pinkish; no obvious lines of blue spots on body, but usually a blue iridescence in each body scale around dorsal and lateral sides of body from some angles; yellow and red membranes only on upper and lower caudal-fin lobes, respectively (the two colors are strongly contrasted; Fig. 3 A–C); somewhat deeper body, 39–43 (mean 41%) of SL; no bony bulge before and above eye; caudal fin moderately forked.

Polysteganus cerasinus n. sp. expressed as percentages of standard length (mean in parenthesis). Description. Counts and proportional measurements as percent of standard length of the holotype and five paratype specimens of Polysteganus flavodorsalis n. sp. are given in Table 2 .

Body depth relatively deeper; head robust, rostro-occipital profile gently convex; interorbital fully scaly, scales extending to nearly above anterior nostrils and just above posterior nostrils, anterior nostrils small and rounded, posterior nostrils slit-like; orbit diameter clearly greater than interorbital width; maxilla naked, its rear end nearly reaching vertical at front edge of eye; rear margin of maxilla not concealed by infraorbitals; jaw robust, especially upper jaw; canines slender and short, 4 in upper and 6 in lower jaw (2 outermost canines in upper jaw somewhat greater than 2 medial canines, and 2 outermost canines of lower jaw considerably larger than 4 medial canines; an outer lateral row of conical teeth and a series of villiform teeth on inner side of outer lateral teeth row; mandibular profile nearly straight; rear margin of preopercle rounded and feebly serrate; a narrow naked area (preopercle with keel-like ridge), between cheek scales and preopercle flange scaly area; first to third dorsal-fin spines progressively longer, fourth dorsal-fin spine longest, but clearly greater than snout length; no sheath scales on dorsal and pelvicfin rays; predorsal-fin length subequal or less than body depth, and clearly less than dorsal-fin base length; lateral line gently curved, subequally parallel to curved dorsal profile from nape to peduncle; pectoral-fin base scaly and rounded posteriorly, 2 or 3 lowest rays slightly extended posteriorly, compared with rays above, creating a concave rear margin for pectoral fins, the fin tip reaching beyond vertical at anal fin origin, its length subequal to or slightly greater than head length; pelvic fin length subequal to fourth dorsal-fin spine length, fin tip not reaching beyond vertical at pectoral-fin tip, but often beyond rear margin of anus; soft dorsal and anal fins with no scales; anal fin with moderate scaly sheath, anal-fin spines slender, second slightly greater than third and clearly less than orbit diameter; caudal fin lobes broad and wide; scales ctenoid; gill-rakers lanceolate; vertebrae 10+14.

Color when fresh, based on color photographs of the holotype and 5 paratypes, photographed by O. Alvheim; head and body uniform pinkish red or orange with blue iridescence at center of each scale, upper head and dorsolateral part of body with more blue iridescence than lower head and abdominal parts of body, and color of snout and upper part of head somewhat yellowish with growth ( Fig. 3 A–C); iris golden and pupil black; all fins generally uniform pinkish.

Color of preserved specimens: upper sides of head and trunk uniform yellowish-tan.

Distribution. Polysteganus flavodorsalis n. sp. is currently known only from Cargados Carajos and Nazareth Bank (11.15°1'S, 61°13.41'E) at a depth of 214 ‒ 305 m.

Etymology. This fish is named for the bright yellow upper margin of the dorsal-fin membranes.

Remarks. Specimens were initially identified as P. coeruleopunctatus because of the uniform pink or red body and similar body proportions of the two species. However, we noticed that this species differs in the dark blue iridescence on the body and the yellow and pink color of the upper and lower caudal fin lobes ( Figs. 3 A–C).

Figures

FIGURE 3. Polysteganus flavodorsalis n. sp. A), SAIAB 84079 (holotype), 143 mm SL, Nazareth Bank, Mascarene Plateau, (15 ° 55.43 ' S, 60 ° 13.38 ' E), Indian Ocean, depth 232 – 236.0 m, photographed by O. Alvheim; B), SAIAB 84183, 134 mm SL, Saya de Malha Bank (10 ° 54.75 ' S, 60 ° 58.17 ' E), Mascarene Plateau, Indian Ocean, depth 127 m, photographed by O. Alvheim; C) SAIAB 84183, 136 mm SL, Saya de Malha Bank, (10 ° 54.75 ' S, 60 ° 58.17 ' E), Mascarene Plateau, Indian Ocean, depth 127 m. Both were photographed by O. Alvheim.

Tables

TABLE 2. Counts and proportional measurements of type specimens of Polysteganus flavodorsalis n. sp. and

	Polysteganus flavodorsalis n. sp.	P. cerasinus n. sp.
	SAIAB 84079 SAIAB 84022, 3 specimens, Holotype (original 247−265 mm SL; SAIAB photograph number 84072, 223 mm SL; SAIAB ACEP08-1531) 84097, 218 mm SL, 5 paratypes n = 1 n = 5	SAIAB 84183 Holotype (original photograph number ACEP08-1704) n = 1
Counts:
Dorsal-fin rays	XII, 10 XII, 10	XII, 10
Anal-fin rays	III, 8 III, 8	III, 8
Pelvic- and pectoral-fin rays	I, 5; 16 I, 5; 15−16	I, 5; 16
Pored lateral-line scales	52 52−53	49
Scale rows between fifth dorsal fin spine base and lateral line	5½ 5½	4½
Scale rows above and below lateral line	6½ / 15½ 6½ / 16½	6½ / 15½
Gill rakers	7 + 13 = 20 6−7 + 12−13 = 19−20	7 + 13 = 20
Standard length	143 mm SL 218−265 mm SL	134 mm SL
Proportions (% SL):
Head length	33.4 35.1−35.6 (35.4)	35.1
Body depth	41.0 39.3−42.5 (41.0)	42.7
Body width at pectoral fin base	15.7 15.7−18.5 (17.4)	16.6
Pectoral-fin ray length	34.3 34.4−36.2 (35.5)	35.7
Snout length	10.8 12.2−14.0 (13.4)	13.8
Upper jaw length	10.3 12.1−12.6 (12.4)	10.7
Interorbital width	11.4 8.6−10.3 (9.4)	10.0
Orbit diameter	13.3 11.4−12.6 (12.0)	12.3
Dermal eye opening	12.0 9.6−10.2 (9.9)	11.2
Suborbital depth	5.6 7.6−8.0 (7.8)	7.4
First dorsal-fin spine length	7.8 6.9−7.6 (7.3)	6.9
Second dorsal-fin spine length	11.3 10.3−11.2 (10.9)	11.2
Third dorsal-fin spine length	14.0 13.2−13.8 (13.4)	14.3
Fourth dorsal-fin spine length	14.8 14.5−15.7 (14.9)	15.1
First dorsal-fin ray length	11.5 10.8−11.5 (11.0)	12.1
First anal-fin spine length	7.6 7.1−7.5 (7.3)	7.2
Second anal-fin spine length	14.7 12.2−13.5 (12.9)	14.3
Third anal-fin spine length	12.5 10.9−14.4 (12.0)	14.1
First anal-fin ray length	12.7 10.7−12.6 (11.5)	14.9
Pelvic-fin spine length	15.5 13.9−15.6 (14.6)	15.1
First pelvic-fin ray length	21.5 20.8−22.7 (21.6)	21.1
Caudal peduncle depth	11.3 10.1−11.6 (10.7)	11.6
Caudal peduncle length	21.6 17.7−20.0 (19.3)	20.3
Predorsal length	38.6 39.5−40.4 (40.0)	41.4
Preanal length	64.8 64.1−66.0 (65.3)	67.2
Prepelvic length	43.7 44.7−46.9 (45.7)	45.5
Dorsal-fin base	53.9 50.0−51.6 (50.8)	51.5
Anal-fin base	16.4 16.2−17.4 (16.6)	16.3