Polysteganus mascarenensis, Iwatsuki & Heemstra, 2011

Iwatsuki, Yukio & Heemstra, Phillip C., 2011, Polysteganus mascarenensis, a new sparid fish species from Mascarene Islands, Indian Ocean, Zootaxa 3018 (1), pp. 13-20 : 14-19

Polysteganus mascarenensis , new species

Proposed English name: Mascarene Red Seabream

Figure 1 ; Tables 1 ‒2

Dentex sp. ; Kyushin et al. 1977: 122‒123, species no. 53, unnumbered color photograph ( Saya de Malha Bank , ca. 10°S, 60°E, southeastern area of Seychelles Islands).

Holotype. SAIAB 84109, 600 mm SL, Mascarene Plateau , Mascarene Islands (15°23.32'S, 61°13.41'E), 258‒288 m depth, coll. by D. Tweddle & O. Alvheim, 19 October 2008.

Paratype. SAIAB 84095, 594 mm SL, Mascarene Plateau , Mascarene Islands (15°41.11'S, 61°04.54'E), 302‒305 m depth, coll. by D. Tweddle & O. Alvheim, 18 October 2008 ; SAIAB 85544, 578 mm SL, same data as the holotype .

Diagnosis. Distinguished from all congeners of Polysteganus by the following combination of characters: dorsal-fin rays XII,10; anal-fin rays III, 8; scales rows between 10th dorsal-fin spine base and lateral line scale 6½; pored lateral line scales 51‒54; snout blunt and broad, its length 2.2‒2.3 times /orbit diameter; bony bulge before and above eye, forming a low median ridge; caudal fin emarginate, nearly truncate if widely spread ( Fig. 1A&B ); mouth large and jaws robust, especially upper jaw; height of posterior end of upper jaw under first two infraorbitals greater than half of orbit diameter (or much greater than pupil diameter)(See arrow in Fig. 1B ); head and body uniform orange-red, dorsally, paler ventrally; all fins uniform reddish orange colour, but membrane of spinous dorsalfin hyaline reddish orange; rear margin of operculum red; no dark blotch on lateral line below middle dorsal-fin spines, and no blue or cobalt longitudinal lines on body.

Description. Counts and proportional measurements as percent of standard length of the holotype and two paratype specimens of Polysteganus mascarenensis n. sp. are given in Table 1.

Body robust, depth 39% SL in holotype (same in paratype); head length 34% SL in holotype (34‒35% SL in paratypes), rostro-occipital profile strongly convex; interorbital scaly, scales extend to nearly above anterior nostrils; nostrils narrow, oval; orbit diameter much less than interorbital width; maxilla naked, its posterior end not reaching vertical at front edge of eye, hind margin of maxilla not concealed by infraorbitals; mouth robust, especially upper jaw; canines short and stout, 4 in upper and 6 in lower jaw (two outermost canines in upper jaw somewhat larger than 2 medial canines); and two outermost canines of lower jaw somewhat smaller than 4 medial canines, but one or two canines are missing in each specimen; an outer lateral row of conical teeth and a series of villiform teeth, on inner side of outer lateral teeth row; mandibular ventral profile convex; hind margin of preopercle rounded and feebly serrated; preopercle flange scaly, the narrow margin naked; a narrow naked area separates the lower scaly area on the cheek and the lower preopercle flange scales; gill-rakers 6+12=18 (6+12=18); first to third dorsal-fin spines progressively longer, fourth dorsal-fin spine longest, but much less than snout length; no sheath scales on dorsal and pelvic-fin rays; predorsal-fin length greater than body depth, and clearly less than dorsal-fin base length; lateral line gently curved, parallel to curved dorsal profile from nape to caudal peduncle; pectoral-fin base scaly and rounded posteriorly, two or three lowest rays somewhat extended posteriorly, compared with rays above, creating a concave posterior margin for the pectoral fins ( Fig. 1A&B ), the fin tip reaching to or slightly beyond vertical at anus, but not reaching anal fin origin, its length clearly less than head length; pelvic fins longer than fourth dorsal-fin spine, fin tip not reaching beyond vertical at pectoral-fin tip and rear margin of anus; soft dorsal and anal fins with no scales; anal fin with moderate scaly sheath, anal-fin spines slender, second and third subequal, greater than orbit diameter; caudal fin lobes broad and wide ( Fig. 1A ), rear margin nearly truncate when widely spread ( Fig. 1B ); scales ctenoid: gill-rakers lanceolate; vertebrae 10+14.

The 594 mm SL paratype (SAIAB 84095), has 11 dorsal-fin spines and 8 dorsal-fin rays but these counts are clearly abnormal. The 12th dorsal-fin spine and the first two dorsal-fin rays are missing, but the dorsal-fin membrane is present across this gap, and the pterygiophores for the 12th dorsal-fin spine and first two dorsal-fin rays are visible on the radiograph of this specimen.

* See notes on Description; ** Counts of gill rakers only for one paratype ( SAIAB 84095 ); gill rakers of other paratype ( SAIAB 85544 ) removed .

Color when fresh. Based on color photographs of the holotype and a paratype (SAIAB 84095) specimen, photographed by D. Tweddle ( Fig. 1A&B ): head and body uniform reddish orange with golden yellow reflections at center of each scale, color of upper head and dorsolateral part of body more vivid than lower head and abdominal part of body; iris golden pupil black; all fins uniform reddish orange, but membrane of spinous dorsal-fin hyaline reddish orange.

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

Distribution. Polysteganus mascarenensis n. sp. is currently known only from the Seychelles, Mascarene Plateau, and Mascarene Islands (15°23.32'S ‒ 15°41.11' S 61°04.54'E ‒ 61°13.41'E) at a depth of 258‒ 305 m. However, the species is likely to have a wider distribution in Indian Ocean because we conclude that the Dentex sp. collected from Saya de Malha Bank, southeastern area of Seychelles Islands ( Kyushin et al. 1977; see Remarks) is conspecific with our P. mascarenensis n. sp.

Etymology. The specific name ” mascarenensis ” refers to the type locality for the species.

Comparison. In five congeners of Polysteganus including P. mascarenensis n. sp., P. undulosus has a large oval dark blotch on lateral line below 5th & 6th dorsal-fin spines (vs. no black blotch in other species; Table 2). Polysteganus praeorbitalis has the greatest body depth at the rear edge of the preopercle and higher counts (14‒16) of lower limb gill-rakers (vs. highest body depth vertically at around the pectoral-fin base and lower counts of lower limb gill rakers, 10‒15 in other species; Table 2). Polysteganus baisacci has lower counts (5½) of scale rows between the fifth dorsal-fin base and lateral line and 7 or 8 longitudinal blue stripes on the body (vs. 6½ scale rows between the fifth dorsal-fin base and lateral line and no longitudinal blue stripes in other species; Table 2). Polysteganus mascarenensis n. sp. can be differed from P. coeruleopunctatus in having 6 ½ scale rows between 10th dorsal-fin spine base and lateral line and no blue or cobalt spotted lines on body (vs. 5 ½ scale rows between 10th dorsal-fin spine base and lateral line and 7 or 8 irregular blue or cobalt spotted lines on body in P. coeruleopunctatus ). Furthermore, P. mascarenensis n. sp. has a broad snout region (snout length/orbit diameter> 2.0), and weakly forked caudal fin (nearly truncate caudal fin if widely spread; Fig. 1A&B , Table 2), strong bony bulge before and above eye, forming a low median ridge ( Fig. 1A&B ), and uniform reddish orange head and body. On the other hand, P. coeruleopunctatus has moderate snout region (snout length/orbit diameter less than 2.0), and forked caudal fin (Table 2), and then does not have such a strong bone bulge before and above eye ( Fig. 1C ), and reddish yellow with strong silvery reflection.

Remarks. Smith (1938) firstly recognized two valid species from the Indian Ocean as a different subgenus under Dentex : Polysteganus coeruleopunctatus and P. undulosus , and then placed another species as the type of a new subgenus, Axineceps praeorbitalis , under Dentex . Subsequently, M.M. Smith (1978) described another new species, Polysteganus baissaci , from Mauritius. Later, Smith & Smith (1986) included A. praeorbitalis as a valid species in the genus Polysteganus . Smith & Smith (1986) concluded that Dentex lineopunctatus Boulenger 1903 and D. natalensis Gilchrist & Thompson 1908 were synonyms of P. coeruleopunctatus . We agree with Smith & Smith’s (1986) conclusion. Accordingly, four valid species of Polysteganus are currently known from Indian Ocean, as noted above.

Diagnostic characters in our Mascarene specimens in this report show a combination of two unique characters within Polysteganus : (1) the head and body uniform reddish orange and (2) a median bony bulge before and above eye, forming a low median ridge ( Fig. 1A&B ) in adults. Smith (1938) noted that “the South African species of Polysteganus have the interorbital scaly, the scales usually covering the whole extent of that region to well in advance of the eye, while the soft dorsal and anal are either basally scaly without sheath, or else have very heavy sheaths”, and also commented that Polysteganus Klunzinger 1870 has priority over Taius ( Jordan & Thompson, 1912; type species Chrysophrys tumifrons Temminck & Schlegel ). Chrysophrys tumifrons is presently identified as Dentex hypselosomus Bleeker (see Iwatsuki et al. 2007) from the northwestern Pacific. In fact, Smith (1938) did not examine this species. While Akazaki (1962) considered that the Atlantic and western Pacific species should be included in Dentex , he did not examine any Indian Ocean species of Polysteganus . Although Western Pacific species of Dentex are similar to Indian Ocean species of Polysteganus in counts and external characters, recent genetic studies have shown polyphyly in Pacific and Atlantic Dentex , and that Indian Ocean Polysteganus species are not congeneric ( Orrell & Carpenter 2004; Chiba et al. 2009). Further taxonomic study of the limits and definitions of these three genera are needed.

Kyushin et al. (1977) published a brief description of a 425 mm SL yellowish red sparid labelled “ Dentex sp. ” from the Saya de Malha Bank (10°S, 60°E, southeastern area of Seychelles Islands)”. The image and description of this specimen agree well with those of Polysteganus mascarenensis ; and we regard this specimen as conspecific with our new species, based on the color photograph of Kyushin et al. (1977) and the following characters: somewhat slender body, similar reddish orange body and all fins; weakly forked caudal fin, same meristic data (scale and fin ray counts), same morphometric data and the collection site (Saya de Malha Bank), being near to the Mascarene Plateau, Mascarene Islands (type locality) of P. mascarenensis n. sp. The color photograph ( Kyushin et al. 1977: p. 122, unnumbered color photograph) also shows important morphological and ontogenetic information in that the smaller specimen (415 mm SL) of this new species has a smaller bony bulge before and above eye; and the snout is relatively shorter ~ 2.0 for snout length divided by orbit diameter (versus 2.0 in our larger specimens), and already greater width of the rear end of the maxilla.

Comparative material examined. Polysteganus baissaci: SAIAB 29 (holotype), 295 mm SL, Northwest of Gunner's Coin [Guoin], Mauritius (19°56'30"S, 57°37'E): SAIAB 1350 (paratype), 251 mm SL, same data as the holotype; SAIAB 59235, 318 mm SL, Soudan Bank, Mauritius.

Polysteganus coeruleopunctatus: HUJ 13901, 2 specimens, 125126 mm SL, Red Sea; SAM 9908 (1 of 2 syntypes of Dentex natalensis ), 283 mm SL, Natal Coast, South Africa; SAIAB 13464, 223 mm SL, off Ras Ngomeni , Ras Ngomeni , Kenya; SAIAB 17470, 318 mm SL, Coffee Bay , Transkei , Eastern Cape, South Africa; SAIAB 29416, 189 mm SL, Coffee Bay , Transkei , Eastern Cape, South Africa; SAIAB 37126, 288 mm SL, 20 miles off Port , KwaZulu-Natal, Durnford Country , South Africa; SAIAB 42816, 332 mm SL, off Kilifi, Mombasa, Kenya; SAIAB 48180, 148 mm SL, off Mozambique (23.47°S, 35.72°E); ZMB 7989 (a syntype of Dentex coeruleopunctatus ), 258 mm SL, Egypt, Red Sea .

Polysteganus praeorbitalis: SAIAB 11646, 244 mm SL, off Cape Receife, Eastern Cape, South Africa ; SAIAB 16573, 287 mm SL, KwaZulu-Natal, South Africa ; SAIAB 37167, 227 mm SL, 20 miles off Port Durnford , KwaZulu-Natal, South Africa .

Polysteganus undulosus: SAIAB 8082, 362 mm SL, Gonubie, East London , Eastern Cape, South Africa; SAIAB 10342, 161 mm SL, Port Alfred , Eastern Cape, South Africa ; SAIAB 15901, 188 mm SL, Rheeders Knoll , 2 km East of Storms River mouth, Eastern Cape, South Africa .

Figures

FIGURE 1. Polysteganus mascarenensis n. sp. A), SAIAB 84109 (holotype), 600 mm SL; B) SAIAB 84095 (paratype), 574 mm SL. Both were photographed by D. Tweddle. Arrow shows the height of posterior end of upper jaw under first two infraorbitals.