Glossanodon macrocephalus Bineesh & Endo, 2019

Bineesh, Kinattumkara, Nashad, Musaliyarakam, Kumar, K. V. Aneesh & Endo, Hiromitsu, 2019, Glossanodon macrocephalus, a new argentine fish (Argentinidae) from the Arabian Sea, Zootaxa 4688 (2), pp. 289-294 : 290-293

Glossanodon macrocephalus Bineesh & Endo n. sp.

New English name: Kerala argentine

Figures 1–3 ; Table 1

Glossanodon sp. A: Bineesh, 2016: fig. 2, pl. 6.

Holotype. ZSI/ANRC- 22843, 163.7 mm SL, mature female, off Kerala, bottom trawl net, 10º45’27.0”N, 75º14’24.6”E, 510 m depth, collected by K.K. Bineesh, 12 Dec. 2011.

Paratypes. ZSI/ANRC- 22844, 154.6 mm SL, male; ZSI/ANRC- 22845, 163.9 mm SL, male, ZSI/ANRC- 22846, 128.5 mm SL, male; off Kerala, bottom trawl net, 10º48’39.0”N, 75º12’24.6”E, 475 m depth, collected by K.K. Bineesh, 22 Nov. , 2011.

Diagnosis. A species of Glossanodon with the following combination of characters: dorsal-fin rays 10–11; pectoral-fin rays 21–23; anal-fin rays 12–13; pelvic-fin rays 11–12; branchiostegal rays 5; gill rakers on first arch 30–36; vertebrae 47–48; a patch of small conical teeth on middle of lower jaw; no teeth on tongue; predorsal length 49–51% SL; prepectoral length 36–39% SL; prepelvic length 57–58% SL; distance from pelvic to anal-fin origins 26–28% SL; head length 35–39% SL; eye diameter 22–26% HL; snout length 28–30% HL; location of anus immediately anterior to anal-fin origin; a broad longitudinal black stripe above lateral line; a dark spot on the pectoral-fin base; and no pigments on the ventral face between isthmus and pelvic-fin bases.

Description. Proportional measurements and counts are given in Table 1 . Body deep, its depth at dorsal-fin base about 15.0–16.4% of SL, weakly compressed laterally and reaching maximum depth at the pectoral-fin base. Dorsal-fin origin above 17th vertebrae, predorsal length slightly longer than postdorsal. First two dorsal fin-rays unbranched, others bifurcated. Pectoral-fin long, reaching to dorsal-fin origin. Adipose fin slender, moderate in size, its origin above 9th anal-fin ray. Anal-fin origin below the 36th vertebrae. Anal-fin base slightly longer than dorsalfin base. Caudal peduncle moderately long, its length 1.55–1.75 times its depth. Pectoral-fin positioned ventrolaterally. Prepectoral length almost equal to head length. Pelvic-fin origin below 7th dorsal-fin ray and 20th vertebra; length of pelvic to anal-fin origin longer than pectoral to pelvic-fin. Caudal-fin forked.

Head relatively large. Eye moderately small, its length about one fourth of HL. Upper edge of orbit projects slightly above dorsal profile of head. Interorbital width smaller than eye diameter. Snout length slightly larger than eye diameter. Mouth moderately small, maxillary covering lachrymal. Lower jaw slightly projecting beyond upper, its end extending almost to vertical line at anterior rim of eye. No teeth on upper jaws and tongue; 20–25 small, conical teeth arrayed as small patch on vomer. Gill rakers elongate and closely arranged. Branchiostegal rays thin, flat. Anus positioned immediately anterior to the anal-fin origin. Scales large, deciduous; all scales were lost in all examined specimens. Lateral-line scales about 42–44 (scale pocket counts).

Colouration when fresh ( Fig. 1 ). Body whitish and silvery, with longitudinal silver band from the base of opercle to caudal-fin base, wide, bright, becoming narrow at posterior end of caudal portion. Anterior of snout, upper jaws, pupil, dorsal of eye, upper side of opercle blackish. A longitudinal black stripe above lateral line very wide; alternatively composed of faint short bars after dorsal-fin base. All fin bases except adipose fin blackish; round, black spot present on base to half of pectoral fin.

Colour in preservative ( Fig. 2 ). Body pale yellow to ocher (bright colouration faded), with dark brown band originating above opercle to caudal-fin base. Dorsal-fin rays moderately pigmented, but its membrane unpigmented. A large round black spot present on base to half of pectoral fin. All fin bases pigmented. Juglar region not pigment- ed. Peritoneum blackish, densely pigmented.

Etymology. The species name “ macrocephalus is from the Greek ‘macro’, large, and ‘cephalon’, head, in reference to the large head in comparison with those of all congeners. A new English name, Kerala argentine, is proposed for this species.

Distribution. Glossanodon macrocephalus n. sp. is thus far known only from the off Kerala coast, southwestern India. This species is not common in all deepsea areas along the southwestern coast but caught from muddy bottoms, in depths of 475 and 510 m.

Remarks. The new species belongs to the subgenus Glossanodon by having the anus located immediately anterior to the anal-fin origin (vs. well-separated from the origin in Prosoarchus ) ( Cohen 1958). Also, G. macrocephalus notably differs from G. pygmaeus in having more pectoral-fin rays (21–23 vs. 12–14) and more vertebrae (48–50 vs. 43).

The subgenus Glossanodon is divided into three groups by Kobilyansky (1998): leioglossus group (3 species), lineatus group (3 species), and polli group (8 species) ( Endo & Nashida 2010, 2012).

Compared with the leioglossus group, G. macrocephalus is clearly separated from G. leioglossus , G. semifasciatus , and G. microcephalus Endo & Nashida 2012 in having fewer Dorsal-fin rays (1 0–11 vs. 13–14 in G. leioglossus , 11–13 in G. semifasciatus ), middle counts of gill rakers on 1st arch (30–36 vs. 35–40 in G. semifasciatus , 25–30 in G. microcephalus ), larger head (HL 35–39% SL vs. 30–32, 27–29, 25–27), smaller eyes (its diameter 22–26% HL vs. 30–32 in G. microcephalus ), and no teeth on tongue (vs. present in all) ( Endo & Nashida 2010, 2012; Yoshikawa et al. 2018).

Compared with the lineatus group, G. macrocephalus is easily differentiated from Glossanodon danieli Parin and Shcherbachev 1982 , Glossanodon lineatus (Matsubara 1943) , and G. pseudolineatus by having 5 branchiostegal rays (vs. 4 in the other three), fewer vertebrae (48–50 vs. 55–57, 55, 43–44), more gill rakers (30–36 vs. 27–29 in G lineatus , 24–26 in G. pseudolineatus ), large head (HL 37–39% SL vs. 30.7–32.4 in G danieli , 25–27 in G lineatus ), and dentition on lower jaws and tongue (see Endo & Nashida 2010: Table 1 ).

Glossanodon macrocephalus probably belongs to the polli group by having 5 branchiostegal rays, no teeth on tongue, and a dark longitudinal band on the side of body in adult ( Kobilyansky 1998; Endo & Nashida 2010, 2012). Among them, G. macrocephalus is clearly separated from Glossanodon polli Cohen 1958 and Glossanodon struhsakeri Cohen 1970 in having fewer dorsal- (10–11 vs. 12–14 in both), anal- (12–13 vs. 14 in G. polli ), and pelvic-fin rays (11–12 vs. 12–13, 13–15), middle counts of pectoral-fin rays (21–23 vs. 19–22, 23–25), fewer vertebrae (47–48 vs. 50–52 in G. struhsakeri ), and teeth restricted on the middle of lower jaw (vs. teeth entirely in both) ( Endo & Nashida 2010, 2012). Further, G. macrocephalus clearly differs from Glossanodon australis Kobilyansky 1998 and G. kotakamaru Endo & Nashida 2010 in having fewer dorsal- (10–11 vs. 11–12, 12–13) and pelvic-fin rays (11–12 vs. 13–14 in both), fewer vertebrae (47–48 vs. 50, 49–50), large head (HL 35–39% SL vs. 26.6–28.2, 29.4–33.3), small eyes (22–26% HL vs. 29.0–31.2, 31.3–33.3), and longer predorsal length (49–51% SL vs. 45–48 in G. australis ) ( Kobilyansky 1998; Endo & Nashida 2010: table 2). Also, G. macrocephalus is readily distinguished from Glossanodon nazca Parin & Shcherbachev 1982 and Glossanodon elongatus Kobilyansky 1998 in having fewer vertebrae (47–48 vs. 50–51, 49–50), large head (HL 35–39% SL vs. 27.6–28.6, 27.8–30.6), small eyes (its diameter 22–26% HL vs. 26.1–30.4, 33.2–37.6), teeth partly arranged on the middle of lower jaw (vs. teeth entirely in both), and no pigment on the ventral face between isthmus and pelvic-fin bases (vs. densely pigmented in both) (Parin & Shcherbachev 1982; Kobilyansky 1998). Besides, G. macrocephalus is clearly separated from G. mildredae in having fewer dorsal-fin rays (10–11 vs. 13), fewer vertebrae (47–48 vs. 49–51), teeth partly arranged on the middle of lower jaw (vs. teeth entirely), and large head (HL 35–39% SL vs. 13.7–20.8) ( Cohen & Atsaides 1969).

Lastly, G. melanomanus was described based on three specimens collected from the Arabian Sea, off Somalia, which is close to G. macrocephalus in counts of dorsal-, anal-, pectoral-, and pelvic-fin rays, dentition on lower jaw, a black spot on pectoral fin, and a black longitudinal stripe above lateral line. However, G. macrocephalus can be distinguished from G. melanomanus by the large head (HL 35–39% SL vs. 33–34), fewer gill rakers (30–36 vs. 36– 38), smaller eye (its diameter 22–26% HL vs. 26.6–27.7), longer pre-pectoral length (36–39% SL vs. 33.0–33.8), shorter distance between dorsal- and adipose-fin origins (35–37% SL vs. 39.0–40.6), and shorter snout (28–30% HL vs. 30.4–31.9) ( Kobilyansky 1998).

Figures

FIGURE 1. Holotype of Glossanodon macrocephalus n. sp., ZSI/ANRC-22843, 163.7 mm SL.

FIGURE 2. Paratype of Glossanodon macrocephalus n. sp., ZSI/ANRC-22846, 128.5 mm SL.

FIGURE 3. Paratype of Glossanodon macrocephalus n. sp., ZSI/ANRC-22844, 154.7 mm SL, after preservation.