Epigonus atherinoides ( Gilbert, 1905 )

Okamoto, Makoto, 2016, Validity of Epigonus megalops (Perciformes: Epigonidae), Redescription of E. atherinoides, and First Record of E. draco from the Central South Pacific, Species Diversity 21, pp. 177-186 : 182-183

Epigonus atherinoides ( Gilbert, 1905)

[English name: Slender Deepwater Cardinalfish] [Japanese name: Hira-yasemutsu] ( Figs 1C–E , 3–4 ; Tables 1–2)

Hynnodus atherinoides Gilbert, 1905: 618 , pl. 79 [original description, type locality: Pailolo Channel (21°15′59″N, 157°52′12″W), south coast of Oahu, Hawaiian Islands]; Jordan and Jordan 1922: 44 (list and note, Hawaiian Islands); Fowler and Bean 1930: 121 (description, Hawaiian Islands); Tinker 1944 (note, Hawaiian Islands).

Epigonus occidentalis (not of Goode and Bean, 1896): Mayer 1974: 170 (in part); Gon 1985: 222 (key to the Hawaiian species of Epigonus ); Borets 1986: 6 (list, Colahan Seamount, Hawaiian Seamounts); Williams et al. 1996: 153 (list, Western Australia); Hutchins 2001: 32 (list, Western Australia); Hoese et al. 2006: 1114 (based on Williams et al. 1996, Western Australia).

Epigonus atherinoides: Mochizuki 1982: 226 (description, Kyushu-Palau Ridge); Mochizuki and Shirakihara 1983: 202, fig. 2 (description, Hawaiian Islands, Kyushu-Palau Ridge); Mochizuki 1984: 146, pl. 133-Q (color photograph and notes); Parin and Abramov 1986: 176 (description, Nazca and Sala y Gomez Ridges); Parin 1991: 679 (list, Nazca and Sala y Gomez Ridges); Abramov 1992: 95 (notes and key); Hayashi 1993: 682 (key); Chave and Mundy 1994: 397 (list, Hawaiian Archipelago); Mochizuki 1997: 306 (color photograph and notes); Chave and Malahoff 1998: 102 (list, Hawaiian Islands); Gon 1999: 2613 (key and notes); Hayashi 2000: 780 (key); Hayashi 2002: 780 (key); Mundy 2005: 357 (list and notes, Hawaiian Islands); Randall 2007: 217 (notes, Hawaiian Islands); Okamoto and Fukui 2011: 391 (key); Okamoto 2012: 252 (key); Hayashi 2013: 865 (key).

Material examined. 23 specimens, 32.0– 138.3 mm SL. Hawaiian Islands: USNM 51601 , holotype, 93.9 mm SL, 21°15′59″N, 157°52′12″W, south coast of Oahu, 0–386 m depth, 27 March 1902; BPBM 132224, 118.1 mm SL, 21°06′48″N, 156°13′42″W, north of Maui , November 1968; LACM 45967-1 , 32.0 mm SL, 21°33′N, 158°33′W, off Oahu , 4 July 1978 . Kyushu-Palau Ridge: FUMT-P 1569–1577 , 9 specimens, 117.9–153.6 mm SL, 28°06′N, 134°39′E, 550–600 m depth, 17 January 1980 . AUSTRALIA: CSIRO H 2557-13 , 3 specimens, 106.7–138.3 mm SL, 23°41.6′S, 112°35.5′E – 23°42.9′S, 112°35.9′E, west of Cape Farquhar, Western Australia, 612–620 m depth, 26 January 1991; CSIRO H 2603-01 , 122.2 mm SL, 31°16.2′S, 114°50.2′E – 31°16.8′S, 114°50.3′E, southwest of Ledge Point , Western Australia, 613–614 m depth, 9 February 1991; CSIRO H 2603-02 , 96.3 mm SL, same data as CSIRO H 2603-01 . Society Islands: MNHN 2014-0854 , 101.0 mm SL, 16°40′12″S, 151°32′12″W, Tahaa island , 705–755 m depth, 17 October 2009 . Nazca and Sala y Gomez Ridges: ZIN 47331, 5 specimens (photographs), 99.0–133.0 mm SL, 25°01′S, 88°32′W, 540 m depth, 22 October 1979 .

Diagnosis. A species of Epigonus with the following combination of characters: dorsal-fin rays VII-I, 10 or rarely VII-I, 9; pectoral-fin rays 20–22; total gill rakers 20–23; vertebrae 10 + 15; pyloric caeca 11–15; pored lateral-line scales 46–50 + 3–5; scales below lateral line 7–8; opercular spine pungent; maxillary mustache-like processes blunt; ribs on last abdominal vertebra absent or rarely present but reduced; upper margin of pectoral-fin base subequal to level of horizontal line through center of eye; proximal radial of first anal-fin pterygiophore broad; cycloid scales on lateral sides of body; head length 28.9–32.7% SL; upper-jaw length 10.2–11.9% SL; and caudal-peduncle depth 6.4–8.2% SL.

Description. Counts and proportional measurements as given in Table 1. Body elongate, laterally compressed, deepest at pectoral-fin base; nape not humped. Head moderate in size, broad. Maxillary mustache-like processes blunt. Snout short and round, length slightly longer than interorbital width; nostrils closely set at level of upper edge of pupil, anterior nostril without membranous tube, posterior nostril elliptical and lacking dermal flap. Eye large, elliptical, orbital diameter greater than postorbital length; bony rim of orbit raised above dorsal profile; interorbital region concave at center. Mouth large, terminal; gape oblique; posterior margin of maxilla not extending to below center of pupil; lower jaw not projecting when mouth closed; anteriorly projecting teeth or nub-like structures absent on symphysis of lower jaw. Teeth minute, arranged in single row on maxilla and dentary. Small number of minute teeth present on vomer and palatine. Basihyal toothless. Opercular spine strong, pungent, forming ridge; preopercular edges smooth. Origin of first dorsal fin above anterior part of pectoral fin; first dorsal-fin spine minute; third dorsal-fin spine longest; isolated dorsal-fin spine absent between first and second dorsal fins. Spine of second dorsal fin short, thicker than first dorsal-fin spines. Origin of anal fin below anterior portion of second dorsal-fin base; first anal-fin spine minute; second anal-fin spine short, but longer than second dorsalfin spine. Proximal radial of first anal-fin pterygiophore long, broad. Pectoral and pelvic fins short, posterior tips of fins not reaching vertical drawn from anus; upper margin of pectoral-fin base subequal to level of horizontal line through center of pupil. Caudal fin deeply forked. Anus located slightly anterior to vertical line through origin of second dorsal fin. Ribs absent on last abdominal vertebra or reduced ribs present (CSIRO H 2557-13, 1 of 3 specimens, 138.3 mm SL). Supraneural bones 3 (0+0/0+2/1+1/1/). Scales small, deciduous, cycloid, covering whole body except for 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, and 3–5 pored scales on caudal fin. Ventral luminous organ absent.

Color in alcohol. Body and all fins uniformly light-brown ( Fig. 1C–E ); opercular region, tongue except for tip (tan), and posterior half of mouth cavity dark-brown.

Distribution ( Fig. 3 ). Known from the Kyushu-Palau Ridge ( Mochizuki 1982), Hawaiian Islands ( Gilbert 1905), Western Australia (present study), Society Islands (present study), and Nazca and Sala y Gomez Ridges ( Parin 1991), at depths of 386– 755 m.

Comparison. Epigonus atherinoides belongs to the E. constanciae group because of having a pungent opercular spine. The diagnostic characters that distinguish E. atherinoides from E. megalops are mentioned in the Comparison section for E. megalops above. Epigonus atherinoides is similar to E. occidentalis in having the upper margin of the pectoral-fin base at about the same level as a horizontal line through the center of the eye and in (usually) lacking a pair of ribs on the last abdominal vertebra, but differs in having 20–23 gill rakers (vs. 24–26, modally 25 in E. occidentalis ; Table 2). Epigonus atherinoides is similar to E. draco and E. ctenolepis in having a small number of gill rakers ( Table 2) but differs from them in having the upper margin of pectoral-fin base at about the same level as a horizontal line through the center of the eye [vs. lower than such a line in E. ctenolepis ( Fig. 5B ) and E. draco ], a pair of blunt maxillary mustache-like processes (vs. absent) and seven to eight scales below the lateral line (vs. nine scales in E. draco and 12–14 scales in E. ctenolepis ). Furthermore, E. atherinoides differs from the remaining 14 species of the group in having fewer gill rakers (20–23 vs. 28–35 in the others; see Okamoto 2015: table 3).

Remarks. Williams et al. (1996) reported on the species composition of the demersal ichthyofauna caught by trawls on the continental slope off Western Australia. In their checklist, they listed three species of Epigonus : E. macrops , E. occidentalis , and E. robustus (Barnard, 1927) . A number of authors have reported occurrences of E. macrops and E. robustus from the Indo-Pacific ( Mayer 1974; Allen and Cross 1989; Abramov 1992; Okamoto 2012); however, reports of E. occidentalis have been restricted to the western North Atlantic ( Mochizuki and Shirakihara 1983; Abramov 1992; Okamoto 2012). I have re-examined the five specimens originally identified as E. occidentalis by Williams et al. (1996) and re-identified them as E. atherinoides . These specimens represent the first records of E. atherinoides from Australia ( Fig. 3 ). Deepwater cardinalfishes of Australia are represented by seven species, including the first record of E. atherinoides here reported; the other six species are E. denticulatus , E. lenimen (Whitley, 1935) , E. macrops , E. pectinifer , E. robustus , and E. telescopus (Risso, 1810) .

A single MNHN specimen from the Society Islands was identified as E . atherinoides; it represents the first record of this species from the central South Pacific . Another specimen from Madagascar ( MNHN 2014-1583, 117.3 mm SL, 12°52.28′S, 48°07.41′E, 558–592 m depth) is similar to E . atherinoides in having a pair of blunt maxillary mustachelike processes, a slender body, and 23 total gill rakers. This specimen may represent a new record of the species from the western Indian Ocean but it is in extremely poor condition . It is treated here as Epigonus sp. until examination of additional specimens confirms the presence of E. atherinoides in that region.

In a study of deepwater fishes collected by bottom trawl in the Emperor Seamount chain, central North Pacific, Chen (1980) listed “ E. atherinoides ” with a color photograph of the species. Some characters of Chen’s (1980) specimen do not agree with those of E. atherinoides , e.g., body depth (more than 20% SL), absence of an opercular spine, body color (tan), etc. Chen's specimen is most likely E. denticulatus (see Dieuzeide 1950; Mochizuki 1982, 1990; Okamoto and Motomura 2013), an abundant species in the Emperor Seamount chain ( Borets 1986). There is no confirmed report of E. atherinoides from the Emperor Seamount chain to date.

The number of pectoral-fin rays has been reported as an important diagnostic character for species of Epigonus (e.g., Mayer 1974; Ida et al. 2007; Okamoto and Motomura 2013). Mochizuki (1984) provided brief descriptions of the Japanese species of the genus and noted that the number of pectoral-fin rays in E. atherinoides is “19–23 (usually 20)”. However, in the present study, most of the specimens of E. atherinoides , including Japanese specimens (Kyushu-Palau Ridge), had a range of 20–23 pectoral-fin rays, with no remarkable mode of the fin ray counts.

Okamoto (2012, 2015) noted the absence in E. atherinoides of a pair of maxillary mustache-like processes; however, examination of the holotype and other specimens of the species in this study revealed a pair of blunt processes present on the maxillary head. Also, the number of scales below the lateral line was reported as nine by Mochizuki and Shirakihara (1983), based on Gilbert’s (1905) illustration of the holotype. My examination of the holotype confirmed that there are eight scales below the lateral line based on the scale pockets. The additional specimens from Western Australia and the Society Islands have provided characters for a revised diagnosis of the species.

Figures

Fig. 1. Epigonus megalops (A–B) and E. atherinoides (C–E). A: E. megalops, USNM 70255, holotype, 125.3mm SL, Philippines; B: E. megalops, USNM 147374, paratype, 116.0mm SL, Philippines; C: E. atherinoides, USNM 51601, holotype, 93.9mm SL, Hawaiian Islands; D: E. atherinoides, CSIRO H 2603-01, 122.2mm SL, Western Australia; E: E. atherinoides, MNHN 2014-0854, 101.0mm SL, Society Islands.

Fig. 3. Distributional records of Epigonus megalops (open stars), E. atherinoides (open circles = previous studies; solid circles = present study), and E. draco (open triangles = previous studies; solid triangles = present study).

Fig. 4. Relationships of (A) head length, (B) upper-jaw length, and (C) caudal-peduncle depth to standard length in Epigonus megalops (open triangles) and E. atherinoides (solid circles).

Fig. 5. Position of uppermost margin of pectoral-fin base in two similar species. A: E. megalops, USNM 147374, paratype, 116.0mm SL; B: E.ctenolepis, FUMT-P 1567, holotype, 98.0mm SL.