Acromycter nezumi ( Asano, 1958 )

Ho, Hsuan-Ching, Smith, David G. & Huang, Jian-Fu, 2018, Notes on two rare conger eel species (Anguilliformes: Congridae) found in Taiwanese waters, Zootaxa 4454 (1), pp. 233-237 : 233-235

Acromycter nezumi ( Asano, 1958)

Figs. 1A–C

Promyllantor nezumi Asano, 1958:196 , fig. 2 (type locality: Owashi , Japan).

Acromycter nezumi ( Asano, 1958) : Smith & Kanazawa, 1977:542. Zhang et al., 1989:112.

Specimen examined. NMMB-P 27327, 257 mm TL, Dong-gang, SW Taiwan, South China Sea, bottom trawl, 13 Oct. 2017.

Description of NMMB-P27327. Head length 12.2% TL; preanal 32.3; predorsal 16.7; trunk length 20.1; tail length 67.7; depth at head 3.8; depth at anus 3.2; width at anus 2.7. Snout length 29.9% HL; eye diameter 8.6; interorbital width 14.0; rictus 31.2; gill opening width 11.5; interbranchial width 16.9; pectoral-fin length 23.6.

Body moderately elongate, oval in cross section anteriorly, becoming more compressed posteriorly; tip of tail moderately pointed but not filiform; anus at about anterior third of total length. Dorsal-fin origin slightly behind tip 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 large, slightly larger than eye diameter, its upper end nearly opposite middle of pectoral-fin base; interbranchial width greater than gill opening and eye.

Head small, reflected by the relatively slender body, deepest at about gill opening; snout long, somewhat swollen dorsally, blunt in dorsal view, its length 3.5 times eye diameter, projecting well beyond lower jaw; lower jaw much shorter than snout; fleshy part of snout projecting anteriorly beyond anterior end of intermaxillary tooth patch; rictus below anterior margin of eye. Anterior nostril tubular, near tip of snout, directed ventrolaterally. Posterior nostril large, elliptical, with a slightly raised rim, above eye at anterior portion of interorbital space. Upper lip with a shallow, free, upturned flange, beginning at second infraorbital pore and ending below middle of eye. 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 before pectoral-fin base, 13 before dorsal-fin origin, 38 pores before anal-fin origin; and ca. 140+ total pores.

Head pores vary in size, mostly enlarged ( Fig. 1B ). Supraorbital canal with 3 pores; the first (ethmoidal pore) small, on ventral side of tip of snout, just above lip; the second enlarged, about twice the size of first, above and slightly anterior to it; the third greatly enlarged and immediately above anterior nostril. Infraorbital canal with 5 pores first 4 pores enlarged, along upper lip; the fifth moderately large and behind rictus. No pore on frontal and behind eye. Preopercular canal with 2 pores; mandibular pores 6, 4 along lower jaw, the first very small, at near anterior tip of lower jaw, the third greatly enlarged; and 2 pores behind rictus. Supratemporal commissure with no pore. Predorsal vertebrae 14; preanal vertebrae 36; precaudal vertebrae 50; total vertebrae 166.

Teeth moderately large, conical to blunt ( Fig. 1C ). Intermaxillary in about five transverse rows, connected to maxillary and vomerine teeth, its anterior margin at same level of that of maxillary teeth. Maxillary and mandibular teeth in bands, wider anteriorly, roughly in 5 rows on maxillary and 6 rows on mandibular, narrowing to 1 or 2 rows posteriorly. Vomerine teeth blunt, forming a large, broad oval patch, in about 5 transverse rows.

Coloration. When fresh, body almost uniformly grayish brown with ventral surface of abdomen light grayish; gill chamber, gill opening and mouth cavity blackish; black papillae on roof of mouth. Preserved coloration slightly paler, except for gill chamber became more distinctly black.

Remarks. Our specimen agrees well with the original description ( Asano, 1958, 1962), except for some minor differences. The predorsal length is slightly longer (16.7% vs. 13.1‒16.2% TL) and snout is slightly longer (29.9% vs. 23.1‒29.2% HL), compared to those in Asano’s specimens. The head length is at the largest value and the eye diameter is at the smallest value compared to Asano’s specimens. Moreover, Asano (1958) provided the total lateral-line pores 155‒165, whereas we can count about 140 from our specimen. It is likely the pores on posterior section of lateral-line have been dried out and are not countable.

Figures

FIGURE 1. Acromycter nezumi (Asano, 1958), NMMB-P27327, 257 mm TL. A. lateral view. B. head pores, by Y.-C. Tu. C. tooth pattern, upper jaw (left) and lower jaw (right).