Epigonus exodon, Okamoto, Makoto & Motomura, Hiroyuki, 2012

Okamoto, Makoto & Motomura, Hiroyuki, 2012, Epigonus exodon, a new species of deepwater cardinalfish (Teleostei: Perciformes: Epigonidae) from Réunion, western Indian Ocean, Zootaxa 3453, pp. 84-88 : 85-87

Epigonus exodon sp. nov.

Figs. 1–4 A

Holotype. MNHN 1991-0155, 97.0 mm SL, male, 21°03ʹS, 55°09ʹE, Réunion, western Indian Ocean, 450–480 m depth, 8 September 1982, J. C. Quero.

Paratype. MNHN 2012-0134, 60.2 mm SL, sex unknown, same data as holotype.

Diagnosis. A species of Epigonus with the following combination of characters: opercular spine absent; ribs absent on last abdominal vertebra; anteriorly projecting teeth present on each side of symphysis of lower jaw; tongue narrow; a shallow V-shaped tooth patch present on rear two-thirds of tongue; mustache-like process of maxillary absent; gill rakers 6+20–22=26–28; vertebrae 10+15; pored lateral-line scales 35–37 to end of hypural plus 3 on caudal fin; dorsal fin VII–I, 10; pyloric caeca 7.

Description. Counts for paratype given in parentheses if different from those of the holotype. Dorsal-fin rays VII–I, 10. Anal-fin rays II, 9. Pectoral-fin rays 17 (16). Caudal fin: procurrent rays 8+8 (9+8), segmented unbranched rays 9+8, branched rays 15. Vertebrae: 10+15; ribs absent on last abdominal vertebra. Gill rakers 6+22 (6+20). Pored lateral-line scales 37+3 (35+3). Scales above lateral line 3. Scales below lateral line 8. Pyloric caeca 7.

Body moderately slender, compressed, deepest at pectoral-fin base, nape not humped. Head large, slightly compressed. Mustache-like maxillary process absent. Snout short and rounded, length shorter than interorbital width; two nostrils closely set in front of upper edge of pupil, anterior nostril short and with membranous tube, posterior nostril elliptical without dermal flap. Eye large, round, orbital diameter slightly greater than postorbital length; bony rim of orbit raised above dorsal profile; interorbital region flat. Mouth large, gape oblique; posterior margin of maxilla reaching to below anterior margin of pupil; lower jaw not projecting when mouth closed, 3 anteriorly projecting teeth ( Fig. 2 ) on symphysis of lower jaw (absent). Small conical teeth on both jaws and palatines, upper jaw and palatines teeth arranged in a single row, lower jaw teeth arranged in a single row but in two rows at symphysis. Vomerine teeth minute, 2 teeth restricted to anterior part, no teeth on posterior part (row of teeth extending from anterior part posteriorly along midline of palate). Lingual teeth, villiform, forming shallow Vshaped tooth patch on rear two-thirds of tongue ( Fig. 4 A). Opercular spine absent, without medial ridges; preopercular edges smooth. Origin of first dorsal fin vertically above anterior portion of pectoral fin; first dorsal-fin spine minute; third dorsal-fin spine longest. Spine of second dorsal fin long, thicker than first dorsal-fin spines. First and second dorsal fins widely separated by distance greater than snout length. Origin of anal fin vertically below posterior portion of second dorsal-fin base; first anal-fin spine minute; second spine moderately thick. Posterior tips of pectoral and pelvic fins just reaching vertical line from anus. Spine of pelvic fin long, its length subequal to second dorsal-fin spine. Caudal fin deeply forked. Anus vertically below origin of second dorsal fin. Abdominal vertebrae 10, ribs absent on last vertebra ( Fig. 3 ); caudal vertebrae 15. Supraneural bones three (/0+0/ 0+2/1+1/1/). Scales deciduous, weakly ctenoid, covering the whole body except snout tip anterior to rim of orbit and surface of lips; scales also on bases of second dorsal, anal, and caudal fins; series of pored lateral-line scales complete, 3 pored scales on caudal fin. No trace of luminous organ around belly or visceral organ.

Measurements of the holotype and paratype (in parentheses), as percentage of SL: head length 33.4 (34.2); head width 16.9 (14.0); head height 16.4 (17.3); body depth 23.9 (24.6); body width 14.3 (13.1); caudal-peduncle depth 9.6 (8.8); caudal-peduncle length 28.0 (28.9); orbital diameter 15.5 (14.5); interorbital width 9.6 (9.0); postorbital length 10.4 (13.0); upper-jaw length 14.8 (14.1); lower-jaw length 14.5 (15.8); snout length 7.1 (7.8); pre-1st dorsal-fin length 34.7 (36.2); pre-2nd dorsal-fin length 55.3 (56.6); pre-pectoral-fin length 36.0 (34.7); prepelvic-fin length 41.8 (38.2); pre-anus length 56.3 (55.3); pre-anal-fin length 60.9 (63.8); 1st spine length on 1st dorsal fin 2.7 (3.2); 2nd spine length on 1st dorsal fin 14.9 (15.4); 3rd spine length on 1st dorsal fin 16.0 (tip broken); 2nd dorsal-fin spine length 13.3 (14.1); 1st anal-fin spine length 1.8 (2.3); 2nd anal-fin spine length 13.3 (14.0); pelvic-fin spine length 14.2 (13.6); 1st dorsal-fin base length 11.5 (11.5); 2nd dorsal-fin base length 11.4 (12.5); anal-fin base length 10.5 (10.6); pectoral-fin length 20.2 (20.4); pelvic-fin length 8.9 (9.0).

Color in alcohol ( Fig. 1 ). Body, head, and all fins uniformly brown, except for tan mouth cavity. Distribution. The holotype and paratype were collected off Réunion, western Indian Ocean ( Fig. 5 ), at a depth of 450– 480 m.

Etymology. The specific name exodon is from the Latin exo- (out) and odon (tooth) in reference to the exposed anteriorly projecting teeth on the symphysis of the lower jaw ( Fig. 2 ).

Comparisons. Epigonus exodon belongs to the E. oligolepis group of four similar species as defined by Okamoto and Motomura (2011). Epigonus exodon and E. glossodontus can be distinguished from the other three members in having anteriorly projecting teeth on the symphysis of lower jaw (vs. absent in E. carbonarius , E. devaneyi , and E. oligolepis ; Okamoto and Motomura 2011). Epigonus exodon can be distinguished from E. glossodontus in having a narrow tongue and a shallow V-shaped tooth patch on the rear two-thirds of the tongue (vs. a broad tongue and a deep V-shaped tooth patch on rear three-fourths of tongue in E. glossodontus ; Fig. 4 ).

Gon (1985) reported that small specimens of E. glossodontus (smaller than 50 mm SL) lack the anteriorly projecting teeth of the lower jaw. Our smaller specimen of E. exodon (paratype, 60.2 mm SL) also lacks the projecting teeth. Thus, there is an ontogenetic change in the character. However, E. exodon can be easily distinguished from E. devaneyi by the tooth patch on its tongue (vs. absent in E. devaneyi ). Epigonus exodon differs from E. carbonarius and E. oligolepis in having 26–28 total gill rakers (vs. 21–23 in E. carbonarius and 29–32 in E. oligolepis ) and a narrow tongue (vs. broad in the latter species; Okamoto and Motomura 2011: fig. 2).

Remarks. Epigonus exodon is distributed in the western Indian Ocean, whereas all other members of the E. oligolepis group have been reported from the Pacific and Atlantic oceans ( Fig. 5 ). The new species was collected from a depth of 450– 480 m. This is consistent with all other species of the group, which occur in depths of more than 300 m ( Mayer 1974; Gon 1985; Okamoto and Motomura 2011).

Comparative material. Epigonus devaneyi : BPBM 30277, paratype, 68.5 mm SL, off south end of Necker Ridge, northwestern Hawaiian Islands, 311–347 m depth, 15 October 1976; HUMZ 129680, 40.7 mm SL, 24°54ʹN, 165°36ʹW, off Hawaiian Islands, February 1994. Epigonus glossodontus : BPBM 28611, holotype (photograph), 78.3 mm SL, off Pearl Harbor, Hawaiian Islands, 1 September 1982; BPBM 30278, 4 paratypes, 39.6–61.0 mm SL, same data as holotype. Epigonus oligolepis : UF 43252, 6 specimens, 104.5–150.3 mm SL, 26°11ʹN, 84°43ʹW, Gulf of Mexico, Florida, 300 m depth, 19 September 1985; USNM 207719, 2 paratypes, 52.0– 77.6 mm SL, 12°01ʹN, 61°53ʹW, Caribbean Sea, 384–457 m depth, 4 September 1974.

Figures

FIGURE 1. Epigonus exodon sp. nov., holotype, MNHN 1991 - 0155, 97.0 mm SL.

FIGURE 2. Tip of the lower jaw of Epigonus exodon sp. nov., holotype, MNHN 1991 - 0155. A, dorsal view and B, ventral view. Arrows show the anteriorly projecting teeth.

FIGURE 3. Radiograph of Epigonus exodon sp. nov., holotype, MNHN 1991 - 0155. A, whole body; B, abdomen. Arrow shows the last abdominal vertebra.

FIGURE 4. Dorsal view of the toothed tongues. A, Epigonus exodon sp. nov., paratype, 60.2 mm SL, MNHN 2012 - 0134 and B, E. glossodontus, paratype, 61.0 mm SL, BPBM 30278.

FIGURE 5. Distributional records of the Epigonus oligolepis group, based on present study and literature records (Mayer 1974; Okamoto and Motomura 2011).