Chlopsis bidentatus, Kenneth A. Tighe & John E. McCosker, 2003

Kenneth A. Tighe & John E. McCosker, 2003, Two new species of the genus Chlopsis (Teleostei: Anguilliformes: Chlopsidae) from the Southwestern Pacific., Zootaxa 236, pp. 1-8 : 5-7

Chlopsis bidentatus sp. nov. (Figs. 1, 2, 3B)

Holotype: MNHN 2001-1080 , 167 mm total length, New Caledonia, 23º 48' S, 168º 17' E, depth 444-503 m, captured with beam trawl, Campagne Bathus 3, Station CP 814 , 28 November 1993.

Paratype: MNHN 2001-1078 , 132 mm TL, Fiji, Somo-Somo Strait , 16E 27 í S, 179E 34.8' W, depth 300-370 m, captured with Waren dredge, Campagne Bordau 1, Station DW 1454, 04 March 1999.

Diagnosis. Distinguished from all other members of the genus Chlopsis by the combination of the following characters: pigmentation bicolored, dorsal origin approximately one eye-diameter behind gill opening, and vomerine dentition in two biserial rows anteriorly.

Description. Total vertebrae 125 (128), predorsal vertebrae 11 (11), preanal vertebrae 31 (32), precaudal vertebrae 42 (41). Proportions as percent of TL: predorsal length 13.2 (13.8), preanal length 33.5 (34.2), head length 11.1 (10.3), depth at anus 2.9 (2.6). Proportions as percent of head length: eye diameter 13.4 (13.5), interorbital width 12.1 (10.6), snout length 22.9 (22.1), tip of snout to rictus of jaw 35.0 (33.6).

Body moderately elongate, slightly compressed. Dorsal fin begins slightly more than one eye diameter posterior to gill opening (Fig. 6). Head moderate in length, relatively deep. Snout relatively broad. Gape short, rictus at posterior margin of eye. Anterior nostril tubular, slightly behind tip of snout, directed anterolaterally. Posterior nostril a posteroventrally directed low tubular opening (covered by a flap) on lip in front of vertical from middle of eye.

Lateral line on body absent except for one pore in branchial region, anterior to the gill opening (Fig. 6). Supraorbital pores three: first (ethmoidal) at anteroventral tip of snout, second anteromedial to base of anterior nostril, and last above and behind anterior nostril. Infraorbital pores four: first just behind anterior nostril, second midway between anterior and posterior nostrils, third below posterior nostril, and last below middle of eye. Preoperculomandibular pores five; first near tip of lower jaw, second below interspace between anterior nostril and infraorbital pore 1, third below interspace between infraorbital pores 1 and 2, forth below posterior nostril, and last below and slightly posterior to infraorbital pore 4.

Maxillary teeth (Fig. 3B) conical, slightly recurved, in 2-3 irregular rows, increasing in size from outer to inner, a total of 18-20 teeth in the inner row. Intermaxillary teeth conical, slightly recurved, with approximately 20 teeth in a round patch (more teeth can be seen on a radiograph of the holotype, but only about 20 penetrate through the tissue in the mouth). Mandibular teeth like those of the maxilla, except in 4-5 irregular rows anteriorly, reducing to 2-3 posteriorly, with 16-20 teeth in the inner row. Vomerine dentition shorter and stouter, slightly compressed, in two longitudinal series, weakly biserial anteriorly and uniserial posteriorly, 15-16 slightly larger teeth in the longer inner row, and 7-8 smaller teeth in the outer biserial row. Dentition of paratype very similar in both counts and arrangement to those of the holotype.

Color of body light brown above and distinctly white ventrally; ventral light area strongly demarcated from the darker dorsum of the snout, starting on unpigmented anterior nostril, continuing back above posterior nostril to ventral margin of eye; tip of lower jaw also pigmented (Fig. 6); posterior to eye, dorsal edge of ventral light area becomes more irregular, but extends dorsally to the gill opening; ventral light area then tapers to base of anal fin slightly behind anus, but continues along base of anal fin for approximately 2/3 of body length; anal fin remains unpigmented to near tip of tail; ventral base of caudal fin and posterior portion of anal fin base much darker than rest of body.

Etymology. The name bidentatus is from the Latin bi (two) and dentatus (toothed) in reference to the distinctive vomerine dentition.

Remarks. Chlopsis bidentatus is similar in overall appearance to several other members of the genus Chlopsis . Chlopsis apterus , C. bicollaris and C. kazuko , all from the eastern Pacific Ocean, are all also bicolored. The posterior origin of the dorsal fin (at least one eye diameter behind the gill opening) separates C. bidentatus from C. bicollaris and C. kazuko . Chlopsis apterus , which also has the dorsal origin behind the gill opening, has a higher vertebral number (125-128 in C. bidentatus versus 134-140 in C. apterus ). Chlopsis bicolor , from the Atlantic Ocean, is very similar in both meristics and morphometrics, as well as in its coloration. Several aspects of the dentition of C. bidentatus , especially the anterior biserial vomerine dentition, clearly separate C. bidentatus from C. bicolor . All other species in the genus Chlopsis can be distinguished from C. bidentatus by coloration. Chlopsis olokun , from the eastern Atlantic, is a fairly uniform tan or gray color, while C. dentatus (from the Atlantic and Indian Oceans) and C. slusserorum (described herein from the Pacific) have banded, blotched or mottled coloration.

In the past, differences in vomerine dentition like that described for C. bidentatus would result in the description of a new genus; for example, Robinsia in Böhlke and Smith (1967), and Boehlkenchelys in Tighe (1992). However, due to the overall morphological similarity of this species to that of others in the genus, and the lack of any hypothesis of relationships within the family, we have taken the conservative approach of describing it within the genus Chlopsis . Relationships within the family are being studied by the senior author, and may later determine whether or not this is the correct decision.