Bathycongrus retrotinctus (Jordan & Snyder, 1901)

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 : 140-142

Bathycongrus retrotinctus ( Jordan & Snyder, 1901)

Blackedge conger

Figs. 6D , 10A–C ; Tables 1–3, 7–8

Leptocephalus retrotinctus Jordan & Snyder, 1901:853, fig. 6 (type locality: Tokyo market, Japan) .

Bathycongrus retrotinctus ( Jordan & Snyder, 1901): Ben-Tuvia, 1993:365. Castle, 1995:716. Castle & Smith, 1999:993. Ho et al., 2015:145.

Specimens examined. NMMB-P11910 (4, 288–403), Dong-gang , Ping-tung, Taiwan, 18 Feb. 2011 . NMMB- P11912 (7, 230–351), Dong-gang , 15 Feb. 2011 . NMMB-P11921 (1, 335), Nan-fan-ao, Yi-lan , Taiwan, 11 Mar. 2011 . NMMB-P13154 (3, 250–313), Dong-gang . NMMB-P19177 (2), Dong-gang , 3 Nov. 2011 . NMMB-P21013 (1, 351), Dong-gang , 12 Mar. 2014 . NMMB-P21023 (1, 365), Dong-gang , 12 Mar. 2014 . NMMB-P21775 (1, 271), Dong-gang , 12 Dec. 2013 . NMMB-P23985 (4, 225–289), Dong-gang , 21 Nov. 2015 . NMMB-P26030 (5, 240–278), Dong-gang , 15 Apr. 2017 . NMMB-P25787 (1, 253), Dong-gang , 3 Mar. 2017 . NMMB-P21183 (1, 357), Dong-gang , 2 Apr. 2014 . NMMB-P21009 (1, 332), Dong-gang , 12 Mar. 2014 . NMMB-P27888 (1, 320), NMMB- P27889 (1, 263), Dong-gang , 3 Mar. 2017 . NMMB-P27916 (1, 167, cleared & stained), Dong-shi, Chia-yi, 1 Jul. 2017. NMMB-P28203 (1, 213), Dong-gang , 29 Mar. 2015 . USNM 399865 (1, 360), USNM 399866 (1, 330), 8 Nov. 2009. USNM 400336 (1, 270), USNM 400337 (1, 304+), USNM 400338 (1, 345), USNM 400339 (1, 347+), Dong-gang , 10 Nov 2009 . USNM 404430 (2, 325+–417+), Taiwan, 2009, no further data. Plus some uncatalogued specimens.

Diagnosis. A moderately large and stout species of Bathycongrus with tail short, attenuate; trunk length 1.3–1.5 times head length; vomer with usually 2 enlarged teeth surrounded by small teeth; origin of dorsal fin above or slightly behind pectoral-fin base; preanal vertebrae 36–38, precaudal vertebrae 42–49, total vertebrae 143–151; and preanal lateral-line pores 30–35.

Description. Proportional measurements and meristics are provided in Tables 7–8. Body less elongate, rounded in cross section, becoming more compressed behind anus; head moderately slender, its depth and width slightly less than those of trunk; tip of tail tapering, attenuate, though not filiform; anus near anterior two-fifths of total length; body depth narrows relatively abruptly near posterior end.

Dorsal fin begins over or slightly behind pectoral-fin base, continuous around tip of tail with caudal and anal fins. Anal fin begins immediately behind anus. Pectoral fin well developed. Gill opening relatively large, about same size as eye diameter, its upper end nearly opposite middle of pectoral-fin base; interbranchial broader than gill opening and eye.

Head large, its length 15.7–18.6% TL, deepest at about occiput, tapering anteriorly from this point; dorsal profile nearly flat from occiput to internasal space; snout moderately long and pointed, its length 1.7–2.1 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 third to nearly posterior margin of eye. Eye well developed.

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

Lateral line complete, first pore on each side slightly enlarged, the canal extended to caudal-fin base; 4–6 before pectoral-fin base, 4–7 (mostly 6) before dorsal-fin origin, and 30–35 (same in comparative specimens) pore before anal-fin origin.

Head pores vary in size, mostly enlarged. Supraorbital canal with 3 pores; the first (ethmoidal pore) on ventral side of tip of snout, just above lip; the second enlarged, about twice the size of first, immediately in front of anterior nostril; the third greatly enlarged and immediately above anterior nostril. Infraorbital canal with 5 pores, the first 4 enlarged, along upper jaw; the first at posterodorsal corner of anterior nostril; the second behind and slightly below the first, between anterior and posterior nostrils; the third below the space between posterior nostril and eye; the fourth below anterior half to middle of eye; the fifth small and behind rictus; no pores behind eye. Preoperculomandibular canal with 10 pores, 7 in mandibular section and 3 in preopercular; first mandibular pore very small, near anterior tip of lower jaw, third pore greatly enlarged, seventh pore behind rictus. Supratemporal commissure with 1 single small median pore (cf. Fig.1 ).

Predorsal vertebrae 8–9 [8–10 in comparative specimens]; preanal vertebrae 36–38 [35–38]; precaudal vertebrae 42–49 [45–48]; total vertebrae 143–151 [144–149].

Teeth moderately large, conical ( Fig. 6D ). Intermaxillary teeth largest, curved, in three or four 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. Vomer with 2 (sometimes 1) enlarged teeth surrounded by several smaller teeth.

Coloration. When fresh, dorsal and posterior portions mostly deep gray, central surfaces of head, abdomen and anterior portion of tail pale with some pigment under skin. Vertical fins gray anteriorly, gradually becoming dark gray or black posteriorly, with unclear white margin; caudal fin deep gray. Preserved specimens slightly paler. Stomach pale on surface but black internally; intestine slightly pigmented anteriorly and most parts pale; ventral half of peritoneum unpigmented, gradually covered by denser pepper dots on dorsal half, some large black dots may be present. Gill chamber and mouth cavity pale.

Distribution. Known from Japan, Taiwan, and the Philippines.

Remarks. This species is distinguished by the relatively abrupt decrease in body depth posteriorly ( Figs. 10A, C ). In other species, the body depth decreases more gradually.

Figures

FIGURE 1. Illustration of head pore systematic of a typical Bathycongrus. AN, anterior nostril; IO, infraorbital pores; LL, Lateral-line pores; PN, posterior nostril; POM, preopercular-mandibular pores; SO, supraorbital pores; ST, supratemporal pore (arrowed).

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).

FIGURE 10. Bathycongrus retrotinctus (Jordan & Snyder, 1901). A–B. NMMB-P29026, 323 mm TL. C. NMMB-P27888, 320 mm TL.