Bathycongrus graciliceps, Smith & Ho, 2018

Smith, David G. & Ho, Hsuan-Ching, 2018, The congrid eel genus Bathycongrus of Taiwan, with descriptions of three new species (Anguilliformes: Congridae), Zootaxa 4454 (1), pp. 118-146 : 133-135

Bathycongrus graciliceps sp. nov.

Common name: Slender-head conger

Figs. 3E , 7A–C , Tables 1–3, 7–8

Holotype. NMMB-P9141 (473, female), Daxi , Yilan, NE Taiwan, northwestern Pacific Ocean, 8 Aug. 2008.

Paratype. USNM 399886 (1, 445+, tip of tail damaged), Dong-gang, SW Taiwan, South China Sea, 13 Sep. 2010.

Diagnosis. A moderately large and elongate species of Bathycongrus , deepest near mid-trunk and tapering at both ends to a slender tail and head; head small, about 12.7–13.1% TL, snout acute; trunk long, 2.0–2.1 times head length. Preanal vertebrae 43–46, total vertebrae 163; preanal lateral-line pores 39–41.

Description. Proportional measurements and meristics are provided in Tables 7–8. Morphometric and meristic characters given for holotype with paratype in parentheses. Head length 3.0 (3.1) in PAL, 7.8 (*) in TL; preanal length 2.6 (*) in TL; predorsal length 2.7 (2.6) in PAL, 7.0 (*) in TL; trunk length 1.5 (1.5) in PAL, 4.0 (*) in TL; tail length 1.6 (*) in TL; depth at head 8.9 (*) in PAL, width at head 11.4 (*) in PAL. Snout length 4.0 (3.7) in HL; eye diameter 7.0 (7.5); interorbital width 9.5 (*); upper jaw 2.7 (2.8); gill opening width 9.8 (8.2); interbranchial width 7.0 (6.5); pectoral-fin length 4.3 (3.5).

Body elongate, deepest near mid-trunk and tapering at both ends to slender tail and head, anus at slightly more than 1/3 TL. Trunk long, about twice the length of head. Dorsal fin begins over posterior part of pectoral fin; anal fin begins immediately behind anus; caudal fin confluent with dorsal and anal fins. Pectoral fin relatively small but well developed, narrow and pointed at tip. Gill opening moderate in size, width less than interbranchial space, its upper corner touching lower end of pectoral-fin base.

Head small, distinctly narrower than trunk, 12.7% (13.1%) TL, tapering anteriorly toward a relatively acute snout, rictus below posterior part of eye, upper jaw extending well beyond tip of lower jaw. Eye well developed, about half snout length. Anterior nostril tubular, near tip of snout, directed antero-laterally. Posterior nostril elliptical, about one nostril diameter in front of mid-eye. Snout long and narrowly pointed, its length 1.6 (2.0) times eye diameter, projecting beyond lower jaw; lower jaw longer than snout; fleshy part of snout with a slight median keel on underside, projecting anteriorly beyond anterior end of intermaxillary tooth patch; rictus nearly below middle of eye.

Lateral line complete, first pore on each side slightly enlarged, the canal extended to caudal-fin base; 9 (8) pores before dorsal-fin origin, 6 (6) before pectoral-fin base, 41 (39) before anal-fin origin; total pores not available due to the preservation.

Head pores well developed ( Fig. 7C ). Supraorbital canal with 3 pores; the first (ethmoidal) pore very small, at tip of snout just above edge of upper lip; second larger and somewhat elongate, directly above first pore and before base of anterior nostril; third the largest of all pores, elongate, above anterior nostril. Infraorbital canal with 5 pores; first pore relatively large, directly behind anterior nostril; second large and slit-like, between anterior and posterior nostrils, slightly closer to anterior nostril; third somewhat smaller, below posterior nostril; fourth slightly smaller than third, below mid-eye; fifth small and round, directly behind rictus. Preoperculomandibular canal with 10 pores, 7 in mandibular section and 3 in preopercular; first pore small, near tip of lower jaw; second and third progressively larger, the third the largest in mandibular series; fourth, fifth, and sixth smaller, located between third pore and rictus; seventh behind rictus; 3 preopercular pores in a longitudinal series directly behind mandibular pores, the last one below level of ST canal, no pores in ascending branch. Supratemporal commissure with 1 median pore (paratype has a small lateral pore on right side).

Predorsal vertebrae 10 (11); preanal vertebrae 43 (46); precaudal vertebrae 53 (52); total vertebrae 163 (145+).

Intermaxillary teeth moderately enlarged ( Fig. 3E ), conical, sharp, in about four transverse rows, largely exposed when mouth closed, slightly separated from vomerine and maxillary teeth. Vomerine teeth in a short, elongate patch, some teeth enlarged but not forming an even row. Maxillary and mandibular teeth in multiserial bands, wider anteriorly than posteriorly, outer teeth somewhat larger.

Coloration. In preservative pale brown or tan, slightly darker dorsally.

Etymology. From the Latin gracilis, slender, and ceps, head, referring to the slender head.

Remarks. This distinctive species is characterized by its relatively long trunk and its slender head with an acute snout. Bathycongrus albimarginatus also has a short head and a long trunk, but the head is stouter and the snout much broader. The holotype and paratype are both females with large eggs. The holotype is intact and the paratype is missing part of the tail tip. It is known so far only from Taiwan.

Figures

FIGURE 3. Tooth pattern on upper jaw. A. Bathycongrus bimaculatus sp. nov., NMMB-P7012, paratype. B. B. bleekeri, NMMB-P26214. C. B. castlei sp. nov., NMMB-P21740, paratype. D. B. guttulatus, NMMB-P7607. E. B. graciliceps sp. nov., holotype. F. B. macroporis, NMMB-P29128. Not to scale.

FIGURE 7. Bathycongrus graciliceps sp. nov., holotype, NMMB-P9141, 473 mm TL.