Bathycongrus bimaculatus, 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 : 121-126

Bathycongrus bimaculatus sp. nov.

New common name: Two-spot short-tail conger

Figs. 2A–D , 3A ; Tables 1–6

Holotype. NMMB-P 24393 (163), off Dong-gang, Pingtung, southwestern Taiwan, South China Sea, bottom trawl, ca. 300 m, 6 Nov. 2015.

Paratypes. NMMB-P7012 (1, 157), 5 Dec. 2003; NMMB-P23175 (1, 169), 24 Apr. 2015; NMMB-P23176 (1, 162), 16 Oct. 2013; USNM 437339 (1, 190), 6 Nov. 2015; all collected from near the type locality.

Diagnosis. A small, moderately elongate species of Bathycongrus with head and body compressed; pale color with two black patches on anterior portion of dorsal fin; tail slender, attenuate, though not filiform; trunk length 1.3–1.5 times HL; teeth small, conical, in about four rows on jaws, in a short oval patch on vomer; preanal vertebrae 27–30, precaudal vertebrae 35–37, total vertebrae 109–111; and preanal lateral-line pores 27–29.

Description. Proportional measurements and meristic data are provided in Tables 1–6.

Head length 2.3 (2.3–2.5) in PAL, 6.5 (6.5–7.0) in TL; preanal length 2.8 (2.7–2.8) in TL; predorsal length 2.0 (2.0–2.2) in PAL, 5.7 (5.6–5.8) in TL; trunk length 1.8 (1.7–1.8) in PAL, 5.0 (4.5–5.0) in TL; tail length 1.5 (1.5–1.6) in TL; depth at head 5.8 (5.5–6.7) in PAL, width at head 9.9 (8.4–9.9) in PAL. Snout length 4.2 (3.9–4.3) in HL; eye diameter 5.8 (4.6–5.7); interorbital width 6.6 (6.3–7.5); upper jaw 2.8 (2.7–2.8); gill opening width 8.4 (7.8–9.8); interbranchial width 4.5 (3.9–5.1); pectoral-fin length 3.6 (2.7–3.6).

Body moderately elongate, laterally compressed through the entire length, oval in cross section, becoming more compressed posteriorly; head relatively large, its length 1.3 (1.3–1.5) times in trunk length; tip of tail moderately attenuate; anus slightly behind anterior third of total length.

Dorsal fin begins over middle of appressed pectoral fin, continuous around tip of tail with caudal and anal fins. Anal fin begins immediately behind anus. Pectoral fin well developed, pointed distally with a narrow base. Gill opening relatively small, slightly smaller than eye diameter, its upper end nearly opposite middle of pectoral-fin base; interbranchial width greater than gill opening and eye.

Head relatively large, 15.0% (14.3–15.7%) TL, deepest about midway between gill opening and tip of snout, tapering anteriorly from this point; snout short, blunt anteriorly in dorsal view, its length 1.4 (1.2–1.4) 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 below posterior half of eye.

Anterior nostril tubular, near tip of snout, directed ventrolaterally. Posterior nostril elliptical, with a slightly raised rim, in front of mid-eye level. Upper jaw with flange greatly reduced; lower jaw with downturned flange. Tongue free, long, and broad.

Lateral line complete, first pore on each side slightly enlarged, the canal extended to caudal-fin base; 5 (4–7) before pectoral-fin base, 7 (6–9) pores before dorsal-fin origin, 28 (27–29) before anal-fin origin, and 114 (110–116) in total.

Head pores vary in size, mostly enlarged ( Fig. 2D ). Supraorbital canal with 3 pores; the first (ethmoidal pore) small, on ventral side of snout tip, just ahead lip; the second enlarged and immediately in front of anterior nostril; the third greatly enlarged and immediately above anterior nostril, about same size as anterior nostril. Infraorbital canal with 5 pores, first four enlarged; the first at posterodorsal corner of anterior nostril; the second between anterior and posterior nostrils; the third below posterior margin of posterior nostril; the fourth slightly before vertical through middle of eye; the fifth small and behind rictus; no pores behind eye. Preoperculomandibular canal with 10 (rarely 9) pores; 7 mandibular pores (except 1 paratype with 6), 5 or 6 along lower jaw and 1 behind rictus, the first very small, at anterior tip of lower jaw, the third greatly enlarged; 3 preopercular pores. Supratemporal commissure with no pore.

Predorsal vertebrae 8 (8); preanal vertebrae 28 (27–30); precaudal vertebrae 37 (35–37); total vertebrae 109 (109–111).

Teeth moderately large, conical ( Fig. 3A ). Intermaxillary teeth largest, curved, in 3 transverse rows, separated from maxillary and vomerine teeth, mostly excluded from closed mouth. Maxillary and mandibular teeth in bands, wider anteriorly, roughly in 4 or 5 rows, narrower posteriorly, in 1 to 2 rows; outermost teeth slightly larger than

innermost. Vomerine teeth forming a small triangular patch, 4 transverse rows of small teeth anteriorly followed by several blunt teeth, roughly in 2 rows.

Coloration. In preservative, pale to yellowish brown; lateral and ventral surface of body and abdomen without chromatophores; scattered pigment on each side of anal-fin base; dorsal surface with a darker wash composed of numerous tiny brown chromatophores on either side of dorsal fin. Snout mostly covered by black pigmentation under the skin, extending to level of posterior margin of eye, except for a clearly white band in front of eye; a black patch under skin at about brain chamber; dark pigment outlining supratemporal canal; a large patch of pigment on opercle in front of pectoral-fin base. Pectoral fin with scattered pigment, denser at base. Dorsal fin with two black patches, one at anterior end of fin and one at anterior fourth of fin; each fin ray with slight internal pigment and a black spot at its base; anal fin pale, each ray with slight internal pigment and a black spot at its base. Caudal fin with black base and scattered pigment.

Anterior half of stomach blackish, posterior half unpigmented, internally and externally. Anterior portion of intestine densely covered by black and brown pigment, posterior portion pale with numerous black dots or small patches of pigment. Dorsal third of peritoneum densely covered by black or brown dots, ventral 2/3 unpigmented. Mouth cavity and gill chamber pale.

BATHYCONGRUS

EELS

Distribution. Known only from the type series collected from off Dong-gang, southwestern Taiwan, northern South China Sea, at depth around 200– 300 m.

Etymology. Named for the two black patches on anterior portion of dorsal-fin margin.

Size. A small species; the largest specimen examined is 190 mm TL. Two of the smallest specimens (157 and 163 mm TL) have ovaries containing many maturing eggs.

Remarks. Bathycongrus bimaculatus belongs to the species group with low vertebral counts (109–137), a cluster of small teeth on vomer, and relatively small body size, comprising B. bleekeri , B. unimaculatus , B. trimaculatus and B. parviporus . It differs from above-mentioned species in having relatively few total vertebrae (109–111, vs. 113–120 or 137 in the other species). Among these species, B. bimaculatus is most similar to B. trimaculatus but can be easily separated by the lack of a black blotch on anal fin (vs. a large black blotch on the fin) and 109–111 total vertebrae (vs. 117–119). Table 6 shows the selected characters for comparison of these species.

Figures

FIGURE 2. Bathycongrus bimaculatus sp. nov., A, B. Holotype, NMMB-P24393, 163 mm TL. C. Paratype, NMMB-P7012, 157 mm TL. D. head pores, NMMB-P7012, arrow indicates the ST pore.

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.