Ophichthus bicolor McCosker & Ho

Ho, Hsuan-Ching, 2015, New species of the snake eels Echelus and Ophichthus (Anguilliformes: Ophichthidae) from Taiwan, Zootaxa 4060 (1), pp. 71-85 : 76-80

Ophichthus bicolor McCosker & Ho , sp. nov.

Bicolored snake eel

( Figs. 4–6 ; Table 2 )

Holotype. NMMB-P 18103 (male, 559 mm), SW Taiwan, Dong-gang, Pingtung, bottom trawl, ca. 200 m, 7 Sept. 2012.

Paratypes. 21 specimens, 489–919 mm TL. Collected from nearby the holotype locality by bottom trawl: CAS 234696 (2 spec., 617–641 mm), 10 May 2012; NMMB-P 14077 (490 mm), NMMB-P 14082 (613 mm), 10 Aug. 2011; NMMB-P 16640 (506 mm), 20 Oct. 2011; NMMB-P 17544 (701 mm), 8 Aug. 2012; NMMB-P 21657-61 (5 spec., 521–603), collected with the holotype; NMMB-P 21662-64 (4 spec., 554–612 mm), collected with NMMB- P14082; NMMB-P 5791 (645 mm), 12 Sep. 1966; NMMBP 17544 (696 mm), 8 Aug. 2012; NMMBP 14077 (489 mm), 10 Aug. 2011. Collected from Chang-bin, Taitung, E. Taiwan by hook and line: NMMB-P 16624 (786 mm), 8 Jan. 2012; NMMBP 16891 (919 mm), 10 May 2012. Collected from Ke-tzu-liao, Kaohsiung by bottom trawl, ca. 200 m: NMMB-P 22212 (696 mm), 28 Mar. 2015.

Diagnosis. A moderately elongate species of Ophichthus with: tail 53–58%, head 8.6–10.8%, and body depth at gill opening 2.5–3.4% of total length; dorsal-fin origin behind gill opening by 2.0–2.5 pectoral-fin lengths; pectoral fin pointed, not elongate; posterior nostril a hole above the upper lip, covered by a flap that extends slightly below the edge of the mouth; upper lip lacks barbels; pores small but conspicuous, SO 1+4, IO 4+2, POM 6+2; teeth large and conical, biserial anteriorly on vomer and maxillary, uniserial on mandible; coloration yellowish-tan, strongly contrasting with white throat and belly, fins pale; total vertebrae 155–163, mean vertebral formula 18-64-158.

Holotype Paratypes

TL (mm) 559 489–919 (n=20)

mean range Total vertebrae 160 158.3 155–163

Counts and measurements of the holotype (in mm). Total length 559; head 51.4; trunk 197.6; tail 310; predorsal distance 87; pectoral-fin length 10.0; pectoral-fin base 4.4; body depth ca. 18 at gill openings; body width ca. 14.5 at gill openings; body depth at anus ca. 18.5; body width at anus ca. 16.5; body depth at branchial basket ca. 20; snout 10.6; tip of snout to rictus 19.4; snout overhang beyond tip of lower jaw 1.3; eye diameter 6.3; interorbital width 5.8; gill opening height 6.7; isthmus width 10.8. Lateral-line pores 67, total pores 154. Vertebral formula 19-65-160.

Description. Body moderately elongate ( Fig. 4 ), subcircular to posterior portion of tail, then becoming more compressed, its depth at gill openings 24–38 in TL. Branchial basket slightly expanded. Head 3.3–4.0 in trunk. Head and trunk 2.1–2.3 and head 9.3–11.6 in TL. Snout rounded, moderately acute when viewed from above; underside of snout not bisected by a groove. Lower jaw included, its tip reaching to middle of anterior nostril tube. Upper jaw moderately elongated, rictus well behind a vertical from posterior margin of eye. Eye moderate, slightly behind center of upper jaw, 3.1–3.8 in upper jaw and 6.5–10 in head. Anterior nostrils tubular, extending ventrolaterally from snout at ca. 80o, reaching below upper lip but not reaching tip of chin when directed forward. Posterior nostril a hole above upper lip, covered by a flap that extends below edge of mouth. Barbels absent from upper lip. Dorsal-fin origin well behind pectoral fin by more than 2 pectoral-fin lengths. Median fins low but obvious, ending approximately an eye diameter before the bluntly pointed tail tip. Pectoral fins pointed, not elongate and lanceolate, the longest rays slightly above mid fin.

Head pores small but apparent ( Fig. 5 ). Single median interorbital and temporal pores. Supraorbital pores 1+4 (occasionally 1+3), infraorbital pores 4+2, lower jaw pores 5–7 (mainly 6), preopercular pores 2, supratemporal pores 3. Faint rows of minute sensory papillae are present along nape, along anterior margin of orbit, and in a horseshoe-shaped pattern around base of anterior nostril. Lateral-line pores apparent; 7–9 before gill opening in an arching sequence, 18–22 before dorsal-fin origin; 63–67 before anus, 153–158 in total, the last ca. 2 eye diameters before tail tip.

Teeth ( Fig. 6 ) fang-like, none enlarged, conical, slightly retrorse, and not closely spaced. An intermaxillary rosette of 4–5 teeth followed by an intermaxillary patch of 3 pairs followed by 6–8 uniserial vomerine teeth which decrease slightly in size posteriorly. Maxillary teeth biserial, 7–10 in inner tooth row and 11–14 in outer row. Mandibular teeth uniserial posteriorly; an anterior patch of 3 pairs of teeth at symphysis, followed by 1–3 pairs of teeth; outer row of 13–17 widely spaced teeth on each side, decreasing in size posteriorly.

Coloration when fresh ( Fig. 4 ) yellowish-brown dorsally, strongly contrasting with the white throat and belly, extending to the anus. Dorsal and anal fins yellowish or pinkish with narrow brown margins. Pectoral fin yellowish or pinkish, with a brown patch at its base. Nostrils white, contrasting with brown snout and upper lips. Coloration in preservative yellowish-brown dorsally, strongly contrasting with white throat and belly extending to anus. A yellowish-orange band flanks pale anal fin. Dorsal fin white, flanked by narrow brown bands. Pectoral fin pale, a brown smudge centrally behind base. Nostrils white, contrasting with brown snout and upper lip. Head brown dorsally, fading behind dorsal-fin origin. Lower jaw with brown bands overlying mandibular pore series. Gums pale. Palate and tongue with a speckling of minute dark spots. Peritoneum pale with fine dark speckling along upper wall. Tail tip white.

Size. The largest known specimen is 927 mm TL.

Etymology. From Latin, in reference to its sharply contrasting coloration, to be treated as a noun in apposition.

Distribution. Known from the type series, collected from off Dong-gang, SW Taiwan and off Taitung, SE Taiwan, from ca. 200–400 m depth.

Remarks. This new species would not be mistaken for most other Ophichthus from Taiwan because of its posterior dorsal-fin origin, dentition, jaw length, eye position, and its distinctive body coloration. It is among the largest species of Taiwanese Ophichthus , reaching nearly a meter in length. The new species is similar to O. megalops Asano, 1987 , known from Japan and Taiwan. It differs from megalops in the more anterior location of its dorsal-fin origin (15–19% of TL behind snout tip vs. 24–26%), its mean pre-dorsal vertebral number (18 vs. 29), in its preopercular pores (2 vs. 3), in its posterior anal-fin coloration (pale vs. black), and in having fewer maxillary teeth (8–11 inner row and 11–14 outer row vs. 25–30 inner row and 25–30 outer row teeth). They are quite similar in their tail and head proportions, total vertebral numbers (155–163 vs. 161–163), and in their body depth (25–31 vs. 25–29 times in TL).

The new species is also similar to Ophichthus retrodorsalis Liu, Tang & Zhang, 2010 , known from the holotype collected from Fuzhou, Fujian Province, China. It has a similar dorsal-fin origin and its dentition is also multiserial. One of us (HCH) examined the holotype of O. retrodorsalis and found it to differ from O. bicolor in its coloration (uniformly light brown), pectoral fins (dark), body depth (50 times in TL at gill opening), head length (14.7 times in TL), eye position (posterior margin of orbit above rictus) and in its dentition (triserial throughout). We were unable to obtain its vertebral counts.

Figures

FIGURE 4. Ophichthus bicolor sp. nov. A. NMMB-P 18103, holotype, 559 mm TL, preserved. B. NMMB-P 22212, paratype, 696 mm TL, fresh. C. NMMB-P 17544, paratype, 701 mm TL, fresh. Bars indicate the origins of the dorsal fin (left) and anal fin (right).

FIGURE 5. Semi-diagrammatic illustration of lateral head of Ophichthus bicolor McCosker & Ho, sp. nov., from the holotype. Arrows point to the frontal pore (left) and median pore of supratemporal series (right).

FIGURE 6. Semi-diagrammatic illustration of dentition of Ophichthus bicolor McCosker & Ho, sp. nov., from the holotype. A. Upper Jaw. B. Lower Jaw

Tables

TABLE 2. Counts and proportions (in thousandths) of the holotype and selected paratypes of Ophichthus bicolor sp. nov.

HL/TL	92	95	86–108
Head and trunk/TL	445	445	424–462
Trunk/TL	353	350	336–371
Tail/TL	555	555	531–572
Dorsal fin-origin/TL	156	153	136–183
Pectoral fin-length/HL	292	280	216–340
Pectoral fin-base/HL	86	103	77–128
Upper jaw/HL	377	435	377–484
Snout/HL	206	188	172–215
Eye/HL	123	115	103–135
Depth at GO/HL	31	31	26–41
Width/depth at GO	790	913	790–986
Vertebral count (n=19)
Predorsal vertebrae	19	18.4	15–23
Preanal vertebrae	65	63.9	61–66