Epigonus macrops

Epigonus macrops (Brauer, 1906)

(English name: Luminous Deepwater Cardinalfish) (Figs. 1, 13; Tables 1, 2)

Oxyodon macrops Brauer, 1906: 288, fig. 172 (original description; type locality: west coast of Sumatra, Indonesia; syntype: ZMB 17678); Jordan, 1920: 517 (list); Schultz, 1940: 412 (list); Weber & 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 & 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 & Fechhelm, 2005: 235 (list, Gulf of Mexico); Hoese et al., 2006: 1114 (list, Western Australia); Okamoto & Nakayama, 2016: 79, fig. 1 (description, southeastern Atlantic and Timor Sea).

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

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

Material examined. 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 (Fig. 13).

Diagnosis. Dorsal-fin rays VII-I-I, 10 or rarely VIII-I, 10; pectoral-fin rays 18–20; total gill rakers 18–20; vertebrae 10 + 15; pyloric caeca 8; pored lateral-line scales 45–51 + 3–5; opercular spine absent; maxillary mustache-like processes absent; ribs present on last abdominal vertebra; ventral luminous organ present; tongue toothless.

Measurements (% SL). Data based on Okamoto & Nakayama (2016); counts are given in Table 1. Head length 34.6–37.8; head height 17.4–20.2; body depth 20.8–24.3; body width 14.0–17.7; caudal-peduncle depth 8.9–10.9; caudal-peduncle length 24.4–28.9; orbital diameter 14.7–17.5; interorbital width 10.2–12.0; postorbital length 12.3–14.6; upper-jaw length 13.3–14.8; lower-jaw length 15.9–19.3; snout length 6.7–9.5; pre-first dorsalfin length 36.8–40.1; pre-second dorsal-fin length 57.0–60.3; pre-pectoral-fin length 35.2–39.5; pre-pelvic-fin length 35.8–41.7; pre-anus length 57.0–61.7; pre-anal-fin length 64.3–69.4; first spine length on first dorsal fin 1.2–2.8; second spine length on first dorsal fin 11.5–15.9; third spine length on first dorsal fin 12.3–15.7; second dorsal-fin spine length 4.9–7.8; first anal-fin spine length 1.2–2.7; second anal-fin spine length 4.8–8.8; pelvic-fin spine length 11.7–14.8; first dorsal-fin base length 10.8–16.0; second dorsal-fin base length 9.6–11.3; anal-fin base length 9.3–10.9; pectoral-fin length 16.7–21.3; pelvic-fin length 14.9–16.0.

Distribution. Off tropical east Africa and Walters Shoals, Western Indian Ocean (Mayer 1974; Shcherbachev 1987; Abramov 1992); Sumatra, Western Australia, and Timor Sea, Eastern Indian Ocean (Brauer 1906; Allen & Cross 1989; Williams et al. 1996; Okamoto & Nakayama 2016); Gulf of Mexico, Caribbean Sea, Bahamas, off French Guiana, and Suriname, western North Atlantic (Mayer 1974; Fujii 1983; McEachran & Fechhelm 2005); off Angola, southeastern Atlantic (Okamoto & Nakayama 2016); off Vietnam, South China Sea, (Abramov 1992); Galápagos Islands, eastern Pacific (McCosker & Long 1997; Okamoto et al. 2012); at depths of 120–1100 m.

Comparisons and Remarks. 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 part of the 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 (Okamoto 2016b). Although several authors reported E. macrops from the east coast of Africa (Mayer 1974; Shchelbachev 1987; Abramov 1992), these authors did not provide any data of the examined specimens (spots of the species in Fig. 1 based on their studies). We thus did not examine any specimens from the Western Indian Ocean area.

Epigonus macrops was originally described based on two syntypes from the eastern Indian Ocean (Brauer 1906). Although we did examine the larger specimen of these, deposited in the ZMB, a smaller specimen has been lost.

Epigonus merleni McCosker & Long, 1997 was originally described on the basis a single specimen collected from the Galápagos Islands. It was considered to be distinguished from E. macrops by having 11 + 14 Vertebrae and 57 lateral-line scales, but first author’s examination of holotype of E. merleni revealed that it actually has 10 + 15 vertebrae, 48 + 5 lateral-line scales, and a luminescent window near the pelvic-fin base (see Okamoto et al. 2012). Therefore, they concluded that E. merleni is a junior synonym of E. macrops (Okamoto et al. 2012).