Bathycongrus castlei, 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 : 129-132

Bathycongrus castlei sp. nov.

Castle’s slender conger

Figs. 3C , 5A–C , 6A ; Tables 1–5

Holotype. NMMB-P16586 (immature female, 328), Nan-fang-ao, Yilan, NE Taiwan, western Pacific Ocean , bottom trawl, 16 Jul. 2010.

Paratypes. NMMB-P21740 (ripe female, 328+), NMMB-P26855 (1 mature male, 295+), USNM 441752 (1 ripe female, 350+), Nan-fang-ao, 11 Mar. 2011. NMMB-P29129 (1 immature female, 240), collected with holotype . NMMB-P21736 (1 immature female, 278), Taiwan, no data.

Non-type. NMMB-P21741, (1, 199+), Dong-gang, 6 Feb. 1966.

Diagnosis. A small, slender species of Bathycongrus with tail tapering, filiform; vomerine teeth forming a long triangular patch, one or two slightly enlarged teeth accompanied by several small teeth at front and sides and 4–9 moderately large, blunt teeth behind; dorsal half of head and body deep brown; preanal vertebrae 35–38, precaudal vertebrae 48–50, total vertebrae 160–162; and preanal lateral-line pores 33–36.

Description. Proportional measurements and meristics are provided in Tables 4–5. Head length 2.6 (2.4–2.6) in PAL, 7.4 (7.3–7.4, based on 3 complete types) in TL; preanal length 2.9 (2.8–2.9) in TL; predorsal length 2.2 (2.1–2.2) in PAL, 6.0 (6.0–6.4) in TL; trunk length 1.6 (1.6–1.7) in PAL, 4.6 (4.5–5.0) in TL; tail length 1.5 (1.5–1.6) in TL; depth at head 8.0 (7.1–8.8) in PAL, width at head 9.1 (8.0–10.6) in PAL. Snout length 3.8 (3.7–3.8) in HL; eye diameter 7.0 (6.0–7.0); interorbital width 6.1 (5.6–6.7); upper jaw 2.7 (2.6–3.0); gill opening width 7.6 (7.6–9.5); interbranchial width 4.9 (4.8–6.9); pectoral-fin length 3.2 (3.1–4.2).

Body elongate, rounded in cross section anteriorly, becoming more compressed behind anus and posterior portion; head moderately slender, its depth and width slightly less than those of trunk; trunk moderately long, its length 1.6 (1.4–1.6) times head length; tip of tail tapering and filiform; anus near anterior third of total length when tail is complete.

Dorsal fin begins over middle of 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, smaller than eye diameter, its upper end nearly opposite middle of pectoral-fin base. Interbranchial broader than gill opening and eye.

Head relatively small, its length 13.5 (13.5–13.7)% TL (based on 3 complete types), deepest at about occiput, tapering anteriorly from this point; dorsal profile nearly flat from occiput to internasal space; snout long and broadly pointed, its length 1.9 (1.6–1.9) times of eye diameter, projecting beyond lower jaw; lower jaw longer than snout; fleshy part of snout with a slight median keel on underside (observed from some of paratypes), projecting anteriorly beyond anterior end of intermaxillary tooth patch; rictus nearly below middle of eye.

Anterior nostril tubular, near tip of snout, directed ventrolaterally. Posterior nostril elliptical, with a clear raised rim, in front of eye above mid-eye level. Upper lip with flange strongly reduced; lower lip with a well-developed downturned flange. Tongue free, long, and broad.

Lateral line complete, first pore on each side slightly enlarged, the canal extended to caudal-fin base; 7 (7–9) pores before dorsal-fin origin; 4 (3–4) before pectoral-fin base, 3–5 fewer than predorsal pores; 33 (33–36) before anal-fin origin; total pores not clear due to state of preservation.

Head pores vary in size, mostly enlarged ( Fig. 5C ). Supraorbital canal with 3 pores; the first (ethmoidal pore) on ventral side of snout tip, just above lip; the second enlarged, about twice the size of first, 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, the first 3 pores enlarged; the first at posterodorsal corner of anterior nostril; the second to fourth above the flange; the second and third between anterior and posterior nostrils; the fourth below anterior margin of eye; and the fifth small and behind rictus; no pores behind eye. Preoperculomandibular canal with 10 pores (9 in one side of one paratype), 7 (6) in mandibular section and 3 in preopercular; first mandibular pore very small, near anterior tip of lower jaw, third greatly enlarged, and seventh behind rictus. Supratemporal commissure with a single small median pore.

Predorsal vertebrae 9 (9–10); preanal vertebrae 35 (35–38); precaudal vertebrae 50 (48–50); total vertebrae 162 (130+, 136+, 149+, 160 in paratypes).

Teeth moderately large, conical to granular ( Figs. 3C , 6A ). Intermaxillary teeth largest, curved, in three 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 or 2 rows; outermost teeth slightly larger than innermost. Vomerine teeth forming a long oval patch, 2 (1 or 2) slightly enlarged teeth with several small teeth at front and sides and followed by 9 (4–8) moderately large, blunt teeth behind.

Coloration. Distinctly bicolored dorsoventrally, the boundary slightly below lateral line; deep brown on dorsal surface of head, trunk and anterior half of tail, and on entire posterior half of tail; whitish and semi-transparent on ventral surfaces of head, trunk and anterior half of tail, with scattered black pigment under skin with a clear myomere pattern seen from outside. Pectoral fin and its base slightly pigmented. A patch of black pigment in front of pectoral-fin base and inner wall of gill opening. Mouth cavity and gill chamber pale, except for some small scattered patches of black pigment on roof of mouth in holotype. Vertical fins grayish with broad black margins, gradually becoming entirely black posteriorly, caudal fin black. Stomach black internally and mostly externally, except for some irregular pale patches; intestine uniformly black; peritoneum densely covered by black pepper dots making the membrane brownish, some paratypes also have large black dots loosely but evenly arranged.

Remarks. The vomerine tooth pattern is quite distinctive among the congeners; two slightly enlarged teeth with a few small teeth at front and sides and 6–9 stout or nearly granular teeth behind. It is most similar to B. guttulatus in having similar vertebral formula. However, it has a relatively short trunk, its length 1.4–1.6 times head length (vs. 1.6–1.9 in B. guttulatus ); 33–36 preanal lateral-line pores (vs. 36–40); the third and fourth infraorbital pores before posterior nostril and below anterior margin of eye, respectively (vs. the third below posterior nostril and the fourth below mid-eye); and a different pattern of vomerine teeth ( Figs. 6A vs. 6C).

It is notable that the non-type, NMMB-P21741 (199+ mm TL), has a total 144+ vertebrae. However, the tip of tail is quite tapering and does not look damaged, or at most only few rear vertebrae lost. The tail length is 64.3% TL, not much different from these congeners with complete filiform tails. The coloration on body surface is mostly faded and the most parts of vertical fins are pale, except for the posterior portion. The peritoneum is similar to that of B. castlei , except that the lower part has somewhat scattered pigment. The anterior 2/3 of the stomach is brownish, and the posterior 1/3 is pale. The intestine is pale. There is one row of scattered dots on the lateral body and some internal dots on the ventral side of the abdomen. It also has a slightly different vomerine tooth pattern ( Fig. 6A , last from the left), slightly shorter predorsal distance (42.1% TL), 45 precaudal vertebrae and 32 preanal lateral-line pores. This specimen may represent a different species, but more specimens are needed for further study.

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 5. Bathycongrus castlei sp. nov.. A. NMMB-P16586, holotype, 328 mm TL. B–C, NMMB-P21740, paratype, 328+ mm TL.

FIGURE 6. Vomerine tooth pattern and variation of four Bathycongrus species. Ventral view, anterior to upward. Open dots mean teeth lost or damaged. Not to scale. A. B. castlei. From left to right: NMMB-P29129 (240 mmTL), P16586 (328, holotype), P26855 (295+), P21740 (328+), USNM 441752(350+), P21736(278), 21741 (199). B. B. wallacei, P21026 (420+), P11902 (380), P21020 (344), P21739 (353+). C. B. guttulatus, P4041 (368), P7076 (231), P21737 (310). D. B. retrotinctus, P11912 (318+, 235, 235, 318, 351, 230), P11910 (288).