Eptatretus mccoskeri, MCMILLAN, 1999

Mincarone, M. M., Plachetzki, D., McCORD, C. L., Winegard, T. M., Fernholm, B., Gonzalez, C. J. & Fudge, D. S., 2021, Review of the hagfishes (Myxinidae) from the Galapagos Islands, with descriptions of four new species and their phylogenetic relationships, Zoological Journal of the Linnean Society 192, pp. 453-474 : 462-463

EPTATRETUS MCCOSKERI MCMILLAN, 1999

MCCOSKER’ S HAGFISH

( FIGS 1, 2D, 3C, 5, 6C; TABLES 1–3)

Eptatretus mccoskeri McMillan, 1999: 115 , fig. 2d–g [type locality: Galapagos Islands, 01°06.3’S, 89°06.9’W, depth 704 ft (correct depth 660 ft / 201 m); type series: holotype, CAS 86431; paratypes, SIO 97-75 (2), USNM 344905 (1)].

Eptatretus mccoskeri . – Mok, 2001: 356. – Mok et al., 2001: 1026. – McMillan & Wisner, 2004: 55. – Mincarone & McCosker, 2004: 166. – Møller & Jones, 2007: 64. – McCosker & Rosenblatt, 2010: 172. – Mincarone & Fernholm, 2010: 797. – Knapp et al., 2011: 404. – Ruiz et al., 2011: 30. – Mincarone & McCosker, 2014: 347. – Cruz-Mena & Angulo, 2015: 325. – Angulo & Del Moral-Flores, 2016: 105.

Eptatretus Eptatretus mccoskeri . – Møller & Jones, 2007: 64.

Material examined: CAS 86431, holotype (310 mm), off SE San Cristobal Island, 01°06’19”S, 89°06’56”W, 201 m depth, submersible Johnson Sea Link , baited minnow trap, John E. McCosker, 16 November 1995 . SIO 97–75 , paratype (290 mm), and USNM 344905 , paratype (284 mm), taken with the holotype . MCCDRS 9397 COI, 16S, 2(303–304 mm) and SIO 19-81 COI, 16S, 2 (310– 310 mm), between Santa Cruz and Santa Fé islands, 00°48’00”S, 90°10’12”W, 155 m depth, Valeska Yamile, sta. G1, baited trap, Douglas Fudge et al., 26 May 2019 , 08:01–10:06 h.

Diagnosis: Eptatretus mccoskeri differs from all congeners, except Eptatretus poicilus Zintzen & Roberts, 2015 from New Zealand, by having eight pairs (seven pairs in one specimen of E. mccoskeri ) of gill apertures well-spaced and arranged in a near straight line, and a 3/3 multicusp pattern of teeth. Eptatretus mccoskeri differs from E. poicilus by its number of trunk pores (38–43 vs. 45–50), number of total pores (69–75 vs. 78–86) and by its colour pattern (body purple to purplish brown vs. body strongly mottled with pale brown, dark brown and white-beige) ( McMillan, 1999; Zintzen et al., 2015).

Description: Body elongated, subcylindrical at prebranchial and branchial regions, laterally compressed at trunk and strongly compressed at tail. Rostrum bluntly rounded. Two bilaterally symmetrical nasal-sinus papillae in the dorsal surface of the nasal sinus. Eyespots conspicuous. Three pairs of barbels on head: first two about equal in size (1.5–2.2% TL) and adjacent to opening of nasopharyngeal duct; third pair longer (1.9–2.9% TL) and immediately adjacent to mouth. Ventral finfold absent (occasionally represented by a white line) or low (1–2 mm high), beginning within anterior 1/3 of trunk, extending backwards to cloaca. Caudal finfold well developed, thin, extending around tail to dorsal surface, ending about over cloaca.

Body proportions (in percentage of TL; description of the holotype followed by range of paratypes in brackets): preocular length 7.1 (5.6–6.3); prebranchial length 25.8 (22.6–26.1); branchial length 10.0 (8.8– 13.5); preventral length 51.6 (38.7–53.4); trunk length 49.7 (49.3–56.1); tail length 15.8 (10.6–16.9); body width at PCD 7.3 (6.9–8.6); body depth at PCD (6.6–8.4); body depth including VFF 8.2 (7.7–9.3); body depth excluding VFF 8.2 (7.4–9.1); body depth at cloaca 7.3 (6.8–14.5); tail depth 8.9 (7.1–9.8).

Counts (description of the holotype followed by range of paratypes in brackets): multicusp pattern 3/3; anterior unicusps 10 (8–10); posterior unicusps 9 (8–10); total cusps 51 (44–51). Prebranchial pores 13 (13–16); branchial pores 7 (6–7); trunk pores 43 (38– 43); tail pores 10 (10–12); total pores 73 (69–75).

Eight pairs of gill pouches corresponding to eight pairs of gill apertures (one specimen with seven pairs of gill pouches and apertures). Gill apertures well-spaced and linearly arranged. Last branchial duct confluent with pharyngocutaneous duct on left side, forming a larger aperture. Posterior tip of dental muscle reaches gill pouches 5–6. Ventral aorta branches at gill pouches 6–7.

Colour (in life): body purple to purplish brown; mouth with white margin; barbels white; eyespots visible, but not prominent; gill apertures with white margins; ventral finfold occasionally lighter than body; caudal finfold with white margin ( Fig. 3). Colour in alcohol darker than that described for live specimens.

Distribution and habitat: Galapagos Islands: known from seven specimens collected in two localities: off south-eastern San Cristobal Island, on the top of a seamount at about 201 m depth; and between Santa Cruz and Santa Fé islands, at 155 m depth ( Fig. 1).