Epigonus glossodontus Gon, 1985

Sato, Mao, Ito, Shohei, Fujiwara, Yoshihiro & Koeda, Keita, 2025, First northwestern Pacific records of the deep-sea cardinalfish Epigonus glossodontus (Teleostei, Epigonidae) from the Daito Islands, Japan, ZooKeys 1231, pp. 1-10 : 1-10

Epigonus glossodontus Gon, 1985

Figs 1 , 2 b, c, d [New standard Japanese name: Horaanahisui-yasemutsu ]

Epigonus glossodontus Gon, 1985: 222, figs 1, 2 (holotype locality: off Pearl Harbor, Mamala Bay, Oahu Island, Hawaiian Islands); Okamoto and Motomura 2011: 157–158, figs 2 c, g, 4 b (Oahu and Molokai islands, Hawaiian Islands).

Material examined.

Japan • 1 specimen, 114.8 mm SL; northeast of Minamidaito Island ; 25°50.991'N, 131°17.065'E; 537 m depth; 30 April 2024; collected using suction sampler equipped on KM-ROV; NSMT-P 149549 • 1, 97.7 mm SL; data as for NSMT-P 149549; URIL 1427 • 1 ♀, 98.7 mm SL; northeast of Kitadaito Island ; 25°57.348'N, 131°20.597'E; 343 m depth; 10 May 2024; suction sampler equipped on TripodFinder 2; URIL 1428 • 1, 36.0 mm SL; northeast of Kitadaito Island ; 25°57.351'N, 131°20.595'E; 342 m depth; 10 May 2024; suction sampler equipped on TripodFinder 2; NSMT-P 149550 • 1, 58.5 mm SL; south off of Minamidaito Island ; 25°48.553'N, 131°15.048'E; 478 m depth; 11 May 2024; suction sampler equipped on KM-ROV; URIL 1429 • 1, 54.6 mm SL; data as for URIL 1429; NSMT-P 149551 • 1, 107.3 mm SL; data as for URIL 1429; NSMT-P 149552 . HIGH SEA • 1 ♀, 97.5 mm SL; Kyushu-Palau Ridge, hill west of Kita-Koho Seamount ; 26°43.511'N, 135°16.356'E; 562 m depth; 17 May 2024; suction sampler equipped on Crambon; NSMT-P 149553 .

Description.

Meristic and proportional characters are shown in Table 1 . Body moderately elongated, compressed, deepest at dorsal-fin origin; nape humped; dorsal and ventral profiles gently curved, slightly concave between first and second dorsal fins. First and second dorsal-fin origins above 5 th and 14 th lateral-line scales, respectively. Origin of anal fin below middle of second dorsal fin. Origin of pelvic fin at level of dorsal-fin origin; upper base of pectoral fin slightly anterior to point below dorsal-fin origin. Caudal fin deeply forked, with rounded lobes. Pectoral fin rounded, reaching vertical through anus. Respective distal margins of dorsal and anal fins slightly emarginated.

Head triangular. Snout short, its tip rounded. Eye large, protruding. Pupil circular. Nostrils horizontally level with center of pupil; anterior nostril circular with a short rim directed anteriorly, midway between snout tip and anterior margin of orbit; posterior nostril a vertical slit laterally in front of eye. Mouth small, terminal. Maxillary mustache-like processes absent. Lower jaw slightly projecting; maxilla extending beyond vertical through center of pupil. Conical teeth in a line, decreasing in size posteriorly; upper jaw teeth apparent when mouth closed; two or three large conical teeth projecting anteriorly [not inclined in small specimens ( NSMT-P 149550 and 149551 and URIL 1429)] on each side of mandibular symphysis, posteriorly adjacent to 3–6 mid-sized retrorse conical teeth. Mandibular symphysis sunken, toothless. Vomer spoon-shaped, with diamond-shaped head bearing small conical teeth in two (partly three) rows along midline. Palatine thin, with small conical teeth in two rows on entirety. Minute conical teeth scattered on endopterygoid. Tongue broad, with deeply-forked V-shaped teeth patch (opening rostrally) on posterior three-fourths. Posterior margin of preopercle smooth, membranous, covered by ctenoid scales. Opercle with weak ridge hidden under scales. Ribs absent on last abdominal vertebra.

All rays of second dorsal and anal fins branched; last anal ray bifurcating at base. Two uppermost and lowermost pectoral fin rays unbranched. Third spine of first dorsal fin longest. Lateral line generally arched, highest below middle of first dorsal-fin base, anterior (rising) and posterior (lowering) portions straight; last pored lateral-line scale on end of hypural, followed by three or four pored scales and further three small tubular scales on caudal fin. Almost entire head and trunk scaled, except for around nostrils, upper and lower rips, and gular region; all scales ctenoid, these on snout smaller than others; predorsal scales reaching to snout, level with anterior nostrils; one scale row on cheek, encircling ventral and posterior margins of eye. Small cycloid scales covering second dorsal, anal, and caudal fins, except respective distal margins; basal one-third of pectoral fin scaled; pelvic fin without scales, except for base.

Color — In life, head and body glossy bluish-green; all scales with black margins; ventral surface whitish. Dorsal, anal, pectoral, and caudal fin scaled areas bluish-green, respective distal margins black; scaleless part of pectoral fin translucent gray. Iris silver, dorsally bluish-green.

Fresh specimens with head and body light coppery-brown, ventrum lighter. All scale posterior margins dark brown, resulting in mottled effect on fins; infraorbital and opercular regions pale bluish. First dorsal fin brown, spines pale bluish; cycloid scales edged with brown, with mottled pattern on scaled areas of second dorsal, anal, and caudal fins. Pelvic and pectoral fins translucent, with dense melanophores.

Distribution.

Currently known from Oahu and Molokai islands, Hawaii ( Gon 1985; Okamoto and Motomura 2011), Kitadaito and Minamidaito islands in the Daito Islands, Japan, and Kita-Koho Seamount at Kyushu-Palau Ridge (this study).

Ecological notes.

During the 44 hours of ROV observations near Kitadaito and Minamidaito islands, at least 122 E. glossodontus individuals were sighted at depths between 340–588 m (total depth surveyed 284–1009 m), generally forming sparse schools of several individuals within and around small caves, fissures, and recesses, and slowly swimming a few to some tens of centimeters from the bottom or walls. Swimming was sometimes directed vertically or upside down along the recess walls or ceiling (Figs 1 c , 2 b, c, d ), while a few individuals swam horizontally above the rocky seafloor. Water temperatures in which E. glossodontus were observed ranged from 7.9 to 16.7 ° C, the temperature range over the entire depth surveyed being 3.8 to 18.2 ° C.

The body color of living individuals recorded by the ROVs was overall bluish-green with black-edged scales (Figs 1 c , 2 c ). Although four attempts were made to bring captured individuals to the surface alive, each failed due to decompression, resulting in loss of the bluish-green coloration. Immediately after death, scales were pale blue, but quickly turned coppery-brown (Fig. 1 a, b ). Dissection of two captured females ( NSMT-P 149553 and URIL 1428) revealed well-developed ovaries.

During a subsequent expedition centered on the Kita-Koho Seamount of the Kyushu-Palau Ridge, an ROV dive conducted on a western hill for five hours at depths of 534–778 m, with water temperatures of 5.6–9.3 ° C, recorded more than 10 E. glossodontus individuals at a site with several recesses at 567 m depth with a temperature of 9.3 ° C, where one specimen ( NSMT-P 149553) was collected at a later date.

Figures

Figure 1. Fresh specimens (a, b) and in situ image (c) of Epigonus glossodontus a NSMT-P 149549, 114.8 mm SL b NSMT-P 149551, 54.6 mm SL c not collected, image rotated 90 ° to left.

Figure 2. Habitats of Epigonus glossodontus a overhang on steep slope off Kitadaito Island b inner part of a (indicated by dashed box) c cave with branches off Minamidaito Island d fissure with small recesses on a wall off Minamidaito Island. Arrowheads indicate E. glossodontus.