Synaphobranchus oligolepis, Ho & Hong & Chen, 2018

Ho, Hsuan-Ching, Hong, Wei-Chun & Chen, Hong-Ming, 2018, A new cutthroat eel of the genus Synaphobranchus (Anguilliformes: Synaphobranchidae) from Taiwan, Zootaxa 4454 (1) : -

Synaphobranchus oligolepis sp. nov.

English name: Naked-belly cutthroat eel.

Figs. 1–3 , 4A–B ; Table 1.

Holotype. NMMB-P 26670 (489 mm TL), off Dong-gang, Pingtung, southwestern Taiwan, northern South China Sea, ca. 300 m, bottom trawl, 9 Aug. 2017.

Paratypes (*indicates these with data taken). * NMMB-P7604 (391 mm TL), * NMMB-P7609 (392 mm TL), * NMMB-P25237 (419 mm TL); all collected from off Kaohsiung, southwestern Taiwan , northern South China Sea, ca. 300 m, bottom trawl, 4 Jul. 2004 . * NMMB-P20636 (266 mm TL), Chang-bin , Taitung, southeastern Taiwan, 19 Mar. 2012 . * NMMB-P23547 (275 mm TL), Dong-gang , Pingtung, southwestern Taiwan, 22 Jul. 2016 . NMMB-P25959 (440 mm TL), Chang-bin , 2016. *TOU-AE7151 (455 mm TL), 2 Jul. 2014; *TOU-AE7153 (453 mm TL), 19 Nov. 2014; *TOU-AE6680 (352 mm TL), 2 Nov. 2012; all collected from off Shihtiping, Taitung, eastern Taiwan, longline . TOU-AE7284 (690 mm TL), TOU-AE7285 (502 mm TL), Chang-bin, Taitung, eastern Taiwan .

Non-types. ASIZP 63731 (270 mm TL); ASIZP 63798 (510 mm TL); 22˚37’N 120˚11’E, off Kaoshiung , southwestern Taiwan, 821 m, otter trawl, 29 Aug. 2002 . ASIZP 63729 (295 mm TL), 22˚32’N, 122˚01’E, off Taitung, southeastern Taiwan, 1027 m, otter trawl, 27 Aug. 2003 . ASIZP 75078 (530 mm TL), 22˚13’N, 120˚24’E, off Pintung , southwestern Taiwan, 68–347 m depth, otter trawl, 29 Jul. 2014 . NMMB-P23548 (178 mm TL), 2 Apr. 2014; NMMB-P21180 (167 mm TL); 2 Apr. 2014; TOU-AE5668 (540 mm TL), 24 Jul. 2010; TOU-AE5669 (488 mm TL), 24 Jul.2010; TOU-AE7081 (393 mm TL), 24 Jul. 2010; TOU-AE7266 (199 mm TL), 9 Aug. 2016; TOU- AE7267 (128 mm TL), 9 Aug. 2016; all collected from Dong-gang , southwestern Taiwan, market, bottom trawl.

Diagnosis. A species of Synaphobranchus with the origin of dorsal fin slightly before to about opposite to origin of anal fin; body scale oval in shape; most parts of head and abdomen naked, except for a scaled patch on cheek behind the eyes; pectoral fin pale with a blackish base; mean vertebral formula 28-28-131, precaudal veterbrae 50–56, and total vertebrae 124–135.

Description. Morphometric and meristic data are provided in Table 1. Data of holotype (mm): total length 489; head length 66.3; predorsal length 122; preanal length 147; trunk length 80.7; tail length 342; depth at gill opening 28.9; depth at anus 28.1; width at anus 15.9; snout length 23.5; eye diameter 7.9; interorbital width 11.9; upper jaw length (rictus) 31.8; pectoral-fin length 24.5; length of gill opening 11.7.

Body anguilliform, slender and compressed, gradually tapering posteriorly. Caudal fin region truncated. Greatest body depth at dorsal-fin origin. Pectoral fin well developed, triangular, situated above posterior margin of gill opening. Gill openings at ventral surface of head, externally united at midline and internally separated by body wall. Pelvic fin absent. Dorsal and anal fins confluent with caudal fin. Dorsal-fin origin about same vertical of that of anal fin in most specimens examined, some individuals with origin of dorsal fin forward to the anus and some just slightly behind the anus, predorsal length 24.9–34.1% TL. Anal-fin origin just anterior to anus. Anal-fin rays better developed than those of dorsal fin.

Head not clearly distinguished from trunk, laterally compressed. Mouth terminal, lower jaw projects slightly beyond tip of snout. Jaws long, the gape extends posteriorly beyond the eyes. Anterior nostril tubular, directed anteroventrally. Posterior nostril nearly circular, with low rim restricted to anterior margin. Eye oval to rounded. Gill openings ventral, horizontal, internally united at midline, but internally separated by body wall, slightly anterior to origin of pectoral fin.

Scales oval to slightly elongated ( Figs. 3C , 4B ); a scale patch on cheek between eye and pectoral fin ( Figs. 1C , 3B , 4A ); most of head, nape and abdomen naked ( Figs. 1–3 ); scattered scales may be present on dorsal surface of trunk in a few individuals, others either entirely naked or with damaged skin and not easy to detect.

Teeth conical to fang-like. Teeth on intermaxilla forming a narrow, oval patch, in about 5 (3–5) rows, larger teeth on medial row, few small teeth on each side of the patch; a space between intermaxillary and vomerine teeth; vomer with single row of small fang-like teeth, extending to about 3/4 of length of lower jaw and behind the posterior margin of eye (slightly shorter in some individuals); teeth on both jaws forming narrow bands, gradually expanded posteriorly, narrow on both ends, anterior portion with 2 irregular rows of large teeth, those along the innermost margin larger than outer row and slightly smaller posteriorly, those on the rest of the patch gradually becoming multiserial and villiform ( Fig. 3D ).

Head pore system complete, pores small ( Fig. 3B ). Supraorbital with 5 pores, first pore at underside of tip of snout, second pore at snout tip anterior to anterior nostril, third and fourth pores on dorsal surface of snout, fifth pore at upper corner of anterior margin of eye. A single small adnasal pore at posterodorsal corner of anterior nostril. Infraorbital with 8 pores, first pore below and behind anterior nostril, second to fourth pore along the upper jaw, four pores behind the eye. Paired frontal pores at interorbital space, one at each side. Mandibular with 9 (8–9) pores; preopercular with 2 (2–4) pores, the uppermost pore about below the second lateral-line pore. Supratemporal with 3 pores (if outermost pore counted as first pore of lateral line). Lateral-line pores: before pectoral-fin base 9 (5–10); predorsal 21 (21–33); preanal 28 (24–33); total pores ca. 125 (124–140).

Predorsal vertebrae 21 (21–33); preanal vertebrae 30 (23–31); precaudal vertebrae 53 (50–56); total vertebrae 132 (124–135). Mean vertebral formula 28-28-131.

Coloration. When fresh, body uniformly dark brownish to blackish; lips and fins darker ( Fig. 2 ). When preserved ( Figs. 4A–B ), body deep gray to deep brown dorsally and paler ventrally; some individuals more or less uniformly colored. Lips darker. Dorsal fin with gray or brown base and white margin on most of the length, uniformly black on posterior portion; anterior 2/3 of anal fin with light gray base and broad white margin, gradually becoming light gray base and black margin posteriorly, then uniformly black; caudal fin black. Anus black. Mouth cavity deep gray. Gill chamber dark black. Peritoneum uniformly black.

Distribution. Known from the type series and non-types collected from off eastern and southwestern Taiwan. It may be found in other Taiwanese waters when more investigations are carried out. Precise depths unknown, but some specimens were collected by bottom trawl or hook-and-line at depth around 300–400 meters.

Etymology. The specific name is from the Greek, oligo = few, lepis =scale, derived from its diagnostic character of a large naked region on head and body.

Figures

FIGURE 1. Synaphobranchus oligolepis sp. nov., holotype, NMMB-P26670, 489 mm TL. A. lateral view. B. lateral view of trunk, the boundary of naked and scaled regions are marked by dots, anterior to left. C. lateral view of head, the scaled region is marked by dots. Bars indicate origin of dorsal fin (above) and anal fin (below).

FIGURE 2. Synaphobranchus oligolepis sp. nov. A–B. NMMB-P25959, paratype, 440 mm TL. C. NMMB-P23547, paratype, 275 mm TL. Bars indicate origin of dorsal fin (above) and anus (below).

FIGURE 3. Synaphobranchus oligolepis sp. nov. A. NMMB-P25237, scaled regions are shaded in gray. B. Head pores, NMMB-P7604, bars indicate the frontal pore (left) and median supratemporal pore (right). C. Scales on lateral side of body, from TOU-AE7151. D. Tooth pattern, from the holotype.

FIGURE 4. Head and body scales of three Synaphobranchus species. A–B. Synaphobranchus oligolepis sp. nov., NMMB- P7604. C–D. Synaphobranchus kaupii. C. USNM 372012 (reversed). D. ASIZP 64275. E–F. Synaphobranchus brevidorsalis. E. USNM 117982 (from Japan, reversed). F. ASIZP 64244. Anterior to left, not to scale.