Epigonus draco, Okamoto, 2015

Okamoto, Makoto, 2015, Epigonus draco, a New Species of Deepwater Cardinalfish (Perciformes: Epigonidae) from the Western Pacific, Species Diversity 20, pp. 121-127 : 121-126

Epigonus draco n. sp.

[New English name: Dragon Deepwater Cardinalfish] ( Figs 1–2 ; Table 1)

Epigonus ctenolepis (not of Mochizuki and Shirakihara, 1983): Iwamoto and McCosker 2014: 291, fig. 122 (between Luzon and Mindoro Islands, Philippines).

Holotype. MNHN 2006-0589 , 127.4 mm SL, male, 07°43′34″S, 158°29′24″E, Solomon Islands, 391–623 m depth, 25 October 2004, bottom trawl.

Paratypes. Five specimens. CAS 235796, 160.1 mm SL, male, 13°36′7″N, 120°23′2″E, between Luzon and Mindoro Islands, Philippines, 541–636 m depth, 1 June 2011 . MNHN 2006-0063 , two specimens, 110.0–145.0 mm SL, male and sex unknown, 8°41′16″S, 157°41′27″E, Solomon Islands, 786 m depth, 5 November 2004 . MNHN 2012-0836 , 128.1 mm SL, sex unknown, 15°41′31″S, 167°01′19″E, west of Malo Island , Vanuatu, 481 m depth, 17 September 2006 . MNHN 2006-0684 , 88.8 mm SL, male, same data as holotype .

Diagnosis. A species of Epigonus with the following combination of characters: dorsal-fin rays VII-I, 10; pectoral-fin rays 19–20; total gill rakers 22–23; pyloric caeca 7–9; pored lateral-line scales 47–49+3–4; scales below lateralline 9; vertebrae 10+15; opercular spine present; maxillary mustache-like process absent; ribs absent on last abdominal vertebra; uppermost margin of pectoral-fin base lower than horizontal line through center of eye; proximal radial of first anal-fin pterygiophore slender; and mouth cavity black.

Description. Counts and measurements of holotype and paratypes given in Table 1. Body slender, laterally compressed, deepest at pectoral-fin base; nape not humped. Head large, slightly compressed. Maxillary mustache-like process absent. Snout short and round, length subequal to interorbital width; two nostrils closely set at level of upper edge of pupil, anterior nostril without membranous tube, posterior nostril elliptical without dermal flap. Eye large, round, orbital diameter grater than postorbital length; bony rim of orbit raised above dorsal profile; interorbital region flat. Mouth large, terminal; gape oblique; posterior margin of maxilla extending to below anterior margin of pupil; lower jaw slightly projecting when mouth closed; anteriorly projecting teeth or nub-like structure absent on symphysis of lower jaw. Teeth minute, arranged in single row on maxilla and dentary, in two or three rows on symphysis of lower jaw; vomerine teeth present, forming broad triangular patch; palatine teeth present, arranged in one or two rows. Basihyal toothless. Opercular spine present, pungent, forming ridge ( Fig. 2A ); preopercular edges smooth. Origin of first dorsal fin above anterior part of pectoral fin; first dorsal-fin spine minute; third dorsal-fin spine longest. Spine of second dorsal fin short, thicker than first dorsalfin’s spines. First and second dorsal fins widely separated by gap longer than snout length; isolated dorsal-fin spine absent. Origin of anal fin below posterior portion of second dorsal-fin base; first anal-fin spine minute; second anal-fin spine short, about twice as long as second dorsalfin spine. Posterior tip of pectoral fin not reaching vertical line drawn from anus. Upper margin of pectoral-fin base lower than horizontal line through center of eye ( Fig. 5A ). Caudal fin deeply forked. Anus located slightly anterior to vertical line through origin of second dorsal fin. Ribs absent on last abdominal vertebra ( Fig. 2B ). Supraneural bones three (0+0/0+2/1+1/1/). Scales deciduous, weakly ctenoid except for pored lateral-line scales (cycloid), covering whole body except area anterior to rim of orbit and surfaces of jaws; scales also present on bases of second dorsal, anal, and caudal fins; series of pored lateral-line scales complete, 3–4 pored scales on caudal fin. No trace of luminous organ around belly or visceral organ.

Color when fresh ( Fig. 1B ). Body and all fins uniformly dark-brown with dark-edged scale pockets forming a reticulate pattern on skin (skin of trunk damaged). Head light brown, and opercle silvery-white.

Color in alcohol ( Fig. 1A ). Body and all fins uniformly light-brown with dark-edged scale pockets forming a reticulate pattern on skin. Snout dark-brown; opercular region, posterior half of tongue, and mouth cavity black.

Distribution. The holotype and paratypes were collect- ed from the Philippines, the Solomon Islands, and Vanuatu in the Western Pacific ( Fig. 3 ) at depths of 391– 786 m.

Etymology. The specific name, draco , is a Latin noun (meaning “dragon”) referring to the slender body and distinct scale pattern on the body surface of the new species.

Comparison. Epigonus draco n. sp. belongs to the E. constanciae group defined by Okamoto (2012). The E. constanciae group is distinguished from the other three species groups of the genus (the E. oligolepis group, the E. pandionis group, and the E. telescopus group) in having a pungent opercular spine, more than 40 pored lateral line-scales, and VII-I, 8–10 dorsal-fin rays. Besides E. draco , this species group comprises 17 species as well (Okamoto 2012; Okamoto and Aungtonya 2013): E. affinis Parin and Abramov, 1986 ; E. atherinoides (Gilbert, 1905) ; E. chilensis Okamoto, 2012 ; E. constanciae (Giglioli, 1880) ; E. crassicaudus de Buen, 1959 ; E. ctenolepis Mochizuki and Shirakihara, 1983 ; E. elegans Parin and Abramov, 1986 ; E. heracleus Parin and Abramov, 1986 ; E. lenimen (Whitley, 1935) ; E. machaera Okamoto, 2012 ; E. marimonticolus Parin and Abramov, 1986 ; E. mayeri Okamoto, 2011 ; E. occidentalis Goode and Bean, 1896 ; E. pectinifer Mayer, 1974 ; E. robustus (Barnard, 1927) ; E. thai Prokofiev and Bussarawit in Parin et al., 2012; and E. waltersensis Parin and Abramov, 1986 . Epigonus draco is most similar to E. ctenolepis in having a small number of gill rakers ( Table 2), lacking a pair of ribs on the last abdominal vertebra and a maxillary mustache-like processes, and having the upper margin of pectoral-fin base lower than a horizontal line through the center of the eye, but differs in having nine scales below the lateral line (vs 12–14 scales in E. ctenolepis ), a more slender proximal radial of the first anal-fin pterygiophore ( Fig. 4 ), and a black mouth cavity (vs paler).

Although E. draco n. sp. is similar to E. atherinoides and E. occidentalis in lacking a pair of ribs on the last abdominal vertebra and a maxillary mustache-like processes, the former differs from the latter two in having the uppermost margin of the pectoral-fin base lower than a horizontal line through the center of the eye ( Fig. 5A ) (vs subequal to the center of the eye in E. atherinoides and E. occidentalis : Fig. 5B, C , respectively). Furthermore, E. draco differs in the counts of pyloric caeca (7–9 vs 12–15 in E. atherinoides ) and gill rakers [22–23 (mode 23) vs 24–26 (mode 25) in E. occidentalis ; Table 2]. Epigonus atherinoides is distributed in the Western Central Pacific: the Philippines, the Kyushu-Palau Ridge, and Hawaiian Islands ( Mochizuki and Shirakihara 1983; Mochizuki 1984, 1990), whereas E. occidentalis has been reported from the Caribbean Sea and Gulf of Mexico in the Western Atlantic ( Mayer 1974).

Epigonus thai is so far known only from the holotype collected from the Andaman Sea. Recently, Okamoto and Aungtonya (2013) revealed that the original description of E. thai did not accurately report several important diagnostic characters, and they moved the species from the E. oligolepis group (sensu Okamoto and Motomura 2011) to the E. constanciae group. Epigonus thai is similar to the new species in lacking the maxillary mustache-like process as well as ribs on the last abdominal vertebra; however, the former differs in having higher counts of gill rakers (27 vs 22–23 in E. draco n. sp.) and pyloric caeca (12 vs 7–9).

Epigonus draco n. sp. can be distinguished from the remaining 13 species of the group in having fewer gill rakers (22–23 vs 28 or more in the others; Table 3).

Fishes of the genus Epigonus have a total of 25 vertebrae, with abdominal and caudal vertebral counts of either 10+15 or 11+14 (e.g., Abramov 1992; Parin and Abramov 1986; Okamoto et al. 2011; Okamoto 2012). Epigonus draco belongs to the former group with 10+15 vertebrae and is thus distinguished from the six other species that have 11+14, viz., E. chilensis , E. crassicaudus , E. heracleus , E. lenimen , E. machaera , and E. robustus (see Table 3).

In addition to the above-mentioned E. atherinoides and E. pectinifer of the E. constanciae group, E. cavaticus Ida, Okamoto and Sakaue 2007 , E. denticulatus Dieuzeide 1950 , and E. lifouensis Okamoto and Motomura 2013 are distributed in the Western Pacific. These three species belong to the E. pandionis group defined by Okamoto and Motomura (2013) and can be easily distinguished from E. draco in lacking an opercular spine.

Remarks. In their list of deep-water fishes collected in 2011 in the Verde Island Passage in the Philippines, Iwamoto and McCosker (2014) identified a single specimen of the present genus as E. ctenolepis . This specimen was reexamined and described as a paratype (CAS 235796) of E. draco n. sp. in this study. Epigonus ctenolepis is a rare species, recorded only from off the Pacific coast of Japan ( Mochizuki and Shirakihara 1983; Okamoto and Fukui 2011).

The shape of the proximal radial of the first anal-fin pterygiophore of E. draco distinguishes this species from E. ctenolepis ( Fig. 4 ). This character is also useful for distinguishing species of other percoid fishes, e.g., those in the family Acropomatidae (e.g., Yamanoue and Matsuura 2002, 2004; Okamoto 2014).

Selected characters based on Okamoto (2012) and the distributions of the 18 species of the E. constanciae group, including the new species described herein, are compared in Table 3. Of these species, E. chilensis was originally described from five specimens (166.3–208.3 mm SL) collected off Chilean Patagonia, at depths of 315–340 m ( Okamoto 2012). In the present study, six additional specimens (151.7–186.6mm SL) of E. chilensis collected from near the type locality were found among specimens of the genus deposited in Kyoto University’s Maizuru Fisheries Research Station (FAKU). On the basis of these latter specimens and the original description, E. chilensis is re-diagnosed herein as having the following combination of characters: a pungent opercular spine; ribs on the last abdominal vertebra; a toothless tongue; a blunt maxillary mustache-like process; a minute tubercle on the symphysis of the lower jaw (not formed at <ca. 170 mm SL); the pelvic-fin base located posterior to a vertical drawn from the origin of the pectoral fin; total gill rakers 28–30; vertebrae 11+14; pored lateral-line scales 46–49+4–6; dorsal-fin rays VII-I, 8–10 (mode 9 soft rays); pectoral-fin rays 16–18; pyloric caeca 6–8; body depth 24.2–31.7% SL; orbital diameter 12.4–15.6% SL; lower-jaw length 12.7–14.4% SL; and second anal-fin-spine length 15.9–21.3% SL.

Comparative material. Epigonus chilensis: FAKU 123285–123287, 3 specimens, 173.9–186.6 mm SL, 42°14′S, 74°55′W, off Chilean Patagonia, 29 December 1977; FAKU 123304–123305, 2 specimens, 151.7–183.0 mm SL, 48°32′S, 75°58′W, off Chilean Patagonia, 6 February 1978; FAKU 123333, 172.6 mm SL, 43°10′S, 75°00′W, off Chilean Patagonia, 30 December 1977. Epigonus crassicaudus: FAKU 123330–123332, 123334–123336, 6 specimens, 229.0– 264.7 mm SL, 43°10′S, 75°00′W, off Chilean Patagonia , 30 December 1977 . Epigonus occidentalis: USNM 270526, 62.6 mm SL, 11°02′03″N, 60°47′30″W, Trinidad and Tobago, 90 m depth, 22 September 1964; USNM 393863, 161.8 mm SL, 11°28′N, 74°67′W, off Colombia, Caribbean Sea , 823 m depth, 14 November 1970; USNM 393865 , 2 specimens, 140.2–153.4mm SL, 17°34′N, 62°42′W, north of St . John Is., U.S. Virgin Islands, 699 m depth, 5 June 1967. Epigonus pectinifer: USNM 395256, 90.7 mm SL, 27°76′N, 92°13′W, off Louisiana, U .S .A., 316 m depth, 21 October 2007. Epigonus robustus: CSIRO H 5375-02, 184.7 mm SL, 39°01′S, 46°32′E, southwestern Indian Ocean, 776–1017 m depth, 12 November 1999; CSIRO H 5398-01 , 176.7 mm SL, CSIRO H 5398-02 , 3 specimens, 190.4–197.2 mm SL, 39°01′S, 46°32′E, southwestern Indian Ocean, 712–1067 m depth, 13 November 1999; MNHN 1989-1136, 169.5 mm SL, 38°41′S, 77°41′E, Saint Paul Is ., southern Indian Ocean, 1050– 1110 m depth, 22 July 1986; MNHN 2004-2094, 167.4 mm SL, 31°11′S, 93°58′E, southern Indian Ocean, 552–1075 m depth, 4 July 2002; MNHN 2004-2432, 168.5 mm SL, 27°17′S, 87°21′E, southern Indian Ocean , sampling depth unknown, 2002 . Epigonus thai: PMBC 26430, holotype, 59.2 mm SL, 6°44′N, 98°06′E, Andaman Sea , 303–313 m depth, 23 February 2000 . In addition, other material of Epigonus was listed in Okamoto (2011, 2012) and Okamoto and Fukui (2011) .

Figures

Fig. 1. Epigonus draco n. sp. A, MNHN 2006-0589, holotype, 127.4mm SL, Solomon Islands; B, CAS 235796, paratype, fresh specimen, 160.1mm SL, Philippines (photographed by D. Catania).

Fig. 2. Epigonus draco n. sp., MNHN 2006-0589, holotype, 127.4mm SL. A, opercular region (arrow pointing to pungent opercular spine); B, radiograph of abdomen (arrow pointing to last abdominal vertebra, bearing no ribs).

Fig. 5. Position of uppermost margin of pectoral-fin base in three similar species of Epigonus constanciae group. A, E. draco n. sp., paratype, MNHN 2006-0063, 145.0mm SL; B, E. atherinoides, FUMT 1570, 133.3mm SL; C, E. occidentalis, USNM 393865, 140.2mm SL.

Fig. 3. Collection localities of Epigonus draco n. sp. (solid stars).

Fig. 4. Lateral view of proximal radial of first anal-fin pterygiophore. A, Epigonus draco n. sp., holotype, MNHN 2006-0589, 127.4mm SL; B, E.ctenolepis, holotype, FUMT-P 1567, 98.0mm SL.