Epigonus macrops ( Brauer, 1906 )

Okamoto, Makoto & Nakayama, Naohide, 2016, First Records of the Luminous Deepwater Cardinalfish (Perciformes: Epigonidae), Epigonus macrops (Brauer, 1906), from the Southeastern Atlantic and Timor Sea, Species Diversity 21, pp. 79-83 : 79-82

Epigonus macrops ( Brauer, 1906)

[English name: Luminous Deepwater Cardinalfish] [Japanese name: Kushiba-yasemutsu] ( Fig. 1 )

Oxyodon macrops Brauer, 1906: 288 , fig. 172 (original description; type locality: west coast of Sumatra, Indonesia); Jordan 1920: 517 (list); Schultz 1940: 412 (list); Weber and de Beaufort 1929: 351, fig. 81 (description, based on Brauer, 1906, west coast of Sumatra, Indonesia); Norman 1939: 60 (list).

Epigonus macrops: Mayer 1974: 159 , fig. 4 (description, Indian Ocean, Gulf of Mexico, Caribbean Sea, and northwestern Atlantic); Fujii 1983: 323, unnumbered fig. (description, Suriname and French Guiana); Shcherbachev 1987: 42 (list, Indian Ocean); Allen and Cross 1989: 553 (list, Western Australia); Abramov 1992: 98, table 1 [key and distribution, western North Atlantic (from Florida to Guiana), Indian Ocean (from Tanzania to Sumatra), and South China Sea (off southern Vietnam)]; Williams et al. 1996: 153, appendix 1 (list, Western Australia); Gon 1999: 2613 (key and brief description, off southern Vietnam); Gon 2000: 614 (list, South China Sea, off southern Vietnam); Hutchins 2001: 32 (list, Western Australia); Gon 2003: 1394 (key and list, western North Atlantic); McEachran and Fechhelm 2005: 235 (list, Gulf of Mexico); Hoese et al. 2006: 1114 (list, Western Australia).

Epigonus merleni McCosker and Long, 1997: 126 , fig. 1 (type locality: Galápagos Islands).

Epigonus atherinoides (not of Gilbert, 1905): Horikoshi et al. 1983: 117 (list, Timor Sea, present specimens).

Material examined. 3 specimens, 121.0– 150.8 mm SL. Southeastern Atlantic : CAS 234746 , 121.0 mm SL, female, off Angola, 9°54.09′S, 12°44.47′E, 620–630 m depth, 10 March 2007, bottom trawl, R / V Dr . Fridtjof Nansen , collected by T . Iwamoto . Timor Sea : BSKU 16702, 150.8 mm SL, female, 9°27.0′S, 127°58.6′E – 9°28.5′S, 127°56.1′E, 610– 690 m depth, 18–19 June 1972, beam trawl, R / V Hakuhomaru, collected by O . Okamura ; BSKU 16703, 128.6 mm SL, male, same data as BSKU 16702 .

Other material examined. 13 specimens, 103.7– 202.5 mm SL. Australia: AMS I. 22814-018, 131.6 mm SL, northwest of Port Headland, Western Australia, Indian Ocean , 18°48′00″S, 116°60′00″E, 704 m depth, 6 April 1982; AMS I . 31161-004, 170.5 mm SL, off Cape Cuvier, Western Australia, Indian Ocean, 24°53′67″S, 111°80′83″E, 901 m depth, 28 January 1991; CSIRO H 2562-01 , 178.4 mm SL, west of Quobba Point, Western Australia, Indian Ocean, 24°28′S, 111°51′E, 905 m depth, 28 January 1991; CSIRO H 6575-08 , 126.8 mm SL, northwest of Cape Leveque, Western Australia, Indian Ocean , 14°35′S, 121°21′E, 709 m depth, 26 June 2007 . Indonesia: ZMB 17678, syntype of Oxyodon macrops , 202.5 mm SL, western coast of Sumatra, Indonesia, eastern Indian Ocean , 03°22′01″S, 101°11′05″E, 903 m depth, 21 January 1899 . Galápagos Islands: CAS 86581, holotype of Epigonus merleni , 139.1 mm SL, surface offshore of Cabo Hammond, Isla Fernandina , Galápagos Islands , eastern Pacific , 00°28′S, 91°37′W, February 1995 . Northwestern Atlantic: MCZ 48827, 148.7 mm SL, Caribbean Sea, 11°54′N, 69°18′W, 910 m depth, 4 October 1963; TCWC 6372.09 , 4 specimens, 103.7–145.6 mm SL, Gulf of Mexico, 27°64′N, 91°53′W, 731 m depth, 3 March 1986; TCWC 7003.10 , 2 specimens, 120.6–156.7 mm SL, Gulf of Mexico , 27°14′N, 93°39′W, 792–864 m depth, 8 April 1986 .

Diagnosis. A species of Epigonus with the following combination of characters: pungent opercular spine absent; dorsal-fin rays VII-I-I, 10 or rarely VIII-I, 10; total gill rakers 18–20; vertebrae 10+15; pyloric caeca 8; pored lateralline scales 45–51+3–5; mustache-like maxillary processes absent; ribs presence on last abdominal vertebra; and ventral luminous organ present.

Description. Counts and proportional measurements as given in Table 1. Body elongate, laterally compressed, deepest at pectoral-fin base; nape not humped. Head large, slightly compressed. Mustache-like maxillary process absent. Snout short and round, its length less than interorbital width; two nostrils closely set at level of upper edge of pupil, anterior nostril without membranous tube, posterior nostril elliptical and without dermal flap. Eye large, round, orbital diameter greater than postorbital length; bony rim of orbit raised above dorsal profile; interorbital region concave in middle. Mouth large, terminal; gape oblique; posterior margin of maxilla extending to vertical drawn approximately through center of pupil; lower jaw slightly projecting when mouth closed; anteriorly projecting teeth or nub-like structures absent on symphysis of lower jaw. Curved conical teeth arranged in single row on maxilla and dentary. Small number of minute teeth present on vomer and palatine. Basihyal toothless. Opercular spine weak and flat, not pungent, forming low ridge; preopercular edges smooth. Origin of first dorsal fin above anterior part of pectoral fin; first dor- sal-fin spine minute; third dorsal-fin spine longest; isolated dorsal fin spine present between first and second dorsalfins, not connected to seventh dorsal-fin spine by fin membrane. Spine of second dorsal fin short, thicker than those of first dorsal fin. Origin of anal fin below posterior portion of second dorsal-fin base; first anal-fin spine minute; second anal-fin spine short, subequal in length to second dorsal-fin spine. Posterior tip of pectoral fin just reaching vertical line drawn from anus. Caudal fin deeply forked. Anus located slightly posterior to vertical line through origin of second dorsal fin. Ribs present on last abdominal vertebra. Supraneural bones three (0+0/0+2/1+1/1/). Scales deciduous, weakly ctenoid, 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, 3–5 pored scales on caudal fin. Ventral luminous organ present; luminescent window locat- ed mid-ventrally between anterior pelvic fins.

Color in alcohol ( Fig. 1 ). Body and all fins uniformly light brown; opercular region dark brown; luminous window, tongue, and mouth cavity black.

Distribution ( Fig. 2 ). Known from the western North Atlantic [Gulf of Mexico and Caribbean Sea, Bahamas, off French Guiana and Suriname ( Mayer 1974; Fujii 1983; McEachran and Fechhelm 2005)]; off Angola, southeastern Atlantic (present study); off Vietnam, South China Sea, ( Abramov 1992); Galápagos Islands, eastern Pacific ( McCosker and Long 1997; Okamoto et al. 2012); and Indian Ocean [Sumatra, Western Australia, Timor Sea, off tropical east Africa, Walters Shoals ( Brauer 1906; Mayer 1974; Shcherbachev 1987; Allen and Cross 1989; Abramov 1992; Williams et al. 1996; present study)]; at depths of 120– 1100 m.

Remarks. There are no clear differences in the meristic and morphometric characters between the present specimens and previously recorded specimens, including a syntype of Epigonus macrops ( Table 1). The present study newly revealed that E. macrops is distributed in the southeastern Atlantic (off Angola) and the Timor Sea. Except for an accidental collection from the surface in the Galápagos Islands after a submarine volcanic eruption ( McCosker and Long 1997: CAS 86581), these distributional records are located between 30°N and 35°S at depths greater than 120 m. Thus, this species is distributed on continental slopes in subtropical and tropical regions.

No species of the genus Epigonus had previously been reported from the Timor Sea. This is considered to be due to the dearth of knowledge about the deep-sea fish fauna of the Timor Sea. On the other hand, six other species of the genus have been recorded from around Angola ( Mayer 1974; Abramov 1992; Okamoto et al. 2011), viz., E. affinis Parin and Abramov, 1986 , E. constanciae (Giglioli, 1880) , E. denticulatus Dieuzeide, 1950 , E. mayeri Okamoto, 2011 , E. pandionis (Goode and Bean, 1881) , and E. telescopus (Risso, 1810) .

Epigonus macrops is unique in the genus in having a ventral luminous organ; one of the eight pyloric caeca appears to have become modified into this organ. The luminescent window is located mid-ventrally between the anterior pelvic-fins and is covered by a single large scale (see Mayer 1974: fig. 7; Okamoto et al. 2012: fig. 3). Also, the eighth dorsal-fin spine is isolated between the first and second dorsal fins or, rarely, is connected by a membrane to the seventh spine of the first dorsal fin (expressed as VII-I-I, 10 or VIII-I, 10). This feature is shared with only four other species in the genus and is known as a unique diagnostic character for the E. telescopus group ( Abramov 1992; Okamoto and Motomura 2011, 2013), which comprises E. macrops , E. angustifrons Abramov and Manilo, 1987 (southwestern Indian Ocean, southeastern Atlantic), E. notacanthus Parin and Abramov, 1986 (Nazca Ridge), and E. telescopus (Indian Ocean, Atlantic, southwestern Pacific) ( Mayer 1974; Abramov 1992; Okamoto et al. 2012; Okamoto 2016).

In our examination of specimens of E. macrops , only one specimen (BSKU 16702, 150.8 mm SL) was a female with developed mature ova. This observation represents the first confirmed information about sexual maturity in this species.

Figures

Fig. 1. Two specimens of Epigonus macrops. A, 150.8mm SL, BSKU 16702, Timor Sea; B, 121.0mm SL, CAS 234746, off Angola.

Fig. 2. Distributional records of Epigonus macrops (stars=present study; circles=previous studies).