Ophichthus vietnamensis, Vo & Hibino & Ho, 2019

Vo, Quang Van, Hibino, Yusuke & Ho, Hsuan-Ching, 2019, Ophiacantha scissionis Lee & Stöhr & Bae & Shin 2019, sp. nov., Zoological Studies (Zool. Stud.) 58 (43), pp. 1-14 : 2-4

Genus Ophichthus Ahl, 1789

Ophichthus vietnamensis sp. nov. New English name: Vietnamese Snake Eel ( Figs. 1–2 ; Table 1) urn:lsid:zoobank.org:act:18C99A76-CE7E-4CE2-B2A6-B59FF1121A76

Holotype: OIM-E. 55769, 387 mm TL, male, Ky Ha, Tam Quang commune, Tam Ky district , Quang Nam province (collected from the fish landing ground), by hook and line at depth 40‒60 m, 27 Jun., 2017, collected by Tran T. H.H.

Paratype: OIM-E. 55768, 421 mm TL, a female with ripe eggs, collected with the holotype.

Diagnosis: A species of Ophichthus with posterior nostril above upper lip, covered by a flap that extends well below the edge of mouth and a less elongate body than other members of the genus (both depth 20–25 times in TL). It can be distinguished by the following combination of characters: tail length 56% TL; posterior end of tail thick, broadly pointed; dorsal origin above tip of appressed pectoral fin; pectoral fin broad and rounded; upper lips with a knob-like barbel at anterior margin of posterior nostril; cephalic sensory pores: SO 1 + 4, POM 8 – 9 + 2; teeth moderately large and conical, biserial along entire upper jaw, biserial anteriorly and uniserial posteriorly on lower jaw, uniserial on vomer; coloration yellowish-tan, slightly contrasting with white throat and belly; dorsal fin grayish with pale base, pectoral fin light brownish and anal fin uniformly pale; total vertebrae 121–130, mean vertebral formula 12-52- 125.

Counts and measurements of the holotype (in mm): Total length 387; head 43.4; trunk 126.6; tail 217; predorsal distance 55.4; pectoral-fin length 10.5; head depth 19.1; head width 17.3; body depth at anus ca. 15.1; body width at anus ca. 14.9; body depth at branchial basket ca. 19.1; snout 9.2; tip of snout to rictus 20.7 snout overhang beyond tip of lower jaw 2.0; eye diameter 5.4; interorbital width 8.3; gill opening height 8.3; isthmus width 13.7. Lateral-line pores: 9 on head, 13 before DFO, 51 before anus, and 122 in total. Vertebral formula 13-52-125.

Description: Body moderately elongate ( Fig. 1 ), subcircular to posterior portion of tail, then becoming slightly compressed, its depth at gill openings 19–20 times in TL. Branchial basket slightly expanded. The skin wrinkled on nape and lateral side of tail tip. Head 8.6 (8.2–8.9) in TL. Head and trunk 2.3 in TL. Snout short, broadly rounded when viewed from above and side; underside of snout bisected by a groove. Lower jaw included, its tip reaching to anterior margin of anterior nostril tube. Upper jaw moderately elongated, rictus well behind a vertical from posterior margin of eye. Eye moderate, at center of upper jaw, 3.8 (3.8) in upper jaw and 8.4 (8.0–8.7) in head. Anterior nostril tubular, extending ventrolaterally from snout, reaching below upper lip and chin when directed downward. Posterior nostril a hole above upper lip, covered by a flap that extends well below edge of mouth. A single stout barbel at anterior base of posterior nostril on upper lip; no barbel below eye. Dorsal-fin origin at level of tip of pectoral fin. Median fins low but obvious, ending approximately an eye diameter before the broadly pointed tail tip. Pectoral fins broad and rounded, not elongate or lanceolate, the longest rays at mid fin.

Head pores small but apparent ( Fig. 2a ). Single median interorbital (frontal) and temporal pores. Supraorbital pores 1 + 4, infraorbital pores 4 + 2, mandibular pores 8 on right side and 9 on left side (9 on both sides of the paratype), 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; 9 (8–9) on head, in an arching sequence, 13 (13) before dorsal-fin origin; 51 (51) before anus, 122 (122) in total, the last ca. twice eye diameter before tail tip.

Teeth ( Fig. 2b, c ) moderately large, conical, and closely spaced. Intermaxillary with 6 (3–6) teeth in a curved row, followed by 18 (16–18) uniserial vomerine teeth, which decrease slightly in size posteriorly. Maxillary teeth biserial, with 21 (19–21) in both rows. Mandibular teeth mostly uniserial, with an inner row of 6 teeth anteriorly, decreasing in size posteriorly.

Coloration: When fresh ( Fig. 1 ) yellowish-brown dorsally, slightly contrasting with the white throat and belly, extending to the anus. Dorsal fin gray-brown with a grey margin; anal fin uniformly creamy white. Pectoral fin yellowish-brown. When preserved, yellowish-brown dorsally, slightly contrasting with white throat and belly extending to anus. Dorsal fin grayish with a white base. Pectoral fin grayish. Mouth cavity, palate and tongue white. Peritoneum, stomach and intestine pale. Tail tip white.

Size: The largest known specimen is 421 mm TL, a ripe female.

Etymology: The specific name refers to the type locality ( Vietnam) of the new species.

Remarks: Many Indo-Pacific Ophichthus have similar body measurements. They can be generally distinguished by dentition, color patterns or the relative positions of dorsal-fin origins, the shape of pectoral fins, and vertebral formulae. The new species is most similar to O. asakusae Jordan and Snyder, 1901 which cooccurs in Vietnam. They have pectoral fins shorter than the jaw; but O. asakusae has 3 POP pores (rarely 2) and mostly uniserial maxillary teeth with one to three inner teeth in the middle of the maxilla and the coloration of the dorsal fin has a white margin (vs. 2 POP pores, biserial maxillary teeth and the coloration of the dorsal fins has a grey margin) ( Sumida and Machida 2000; Hibino et al. 2019; and the present study). Additionally, O. vietnamensis sp. nov. is relatively more robust than O. asakusae (body depth at mid-anus 3.9‒4.8% TL vs. 3.0‒4.2%). Ophichthus vietnamensis sp. nov. is also similar to O. urolophus ( Temminck and Schlegel, 1846) in general appearance, but can be separated by the thick tail tip (vs. tail tip narrowly pointed), fewer vertebrae (121‒130 vs. 134‒140) and the dorsal-fin origin at the level of tip of pectoral fin (vs. behind of tip of pectoral fin). Two other species also have a thick tail tip ( O. alleni McCosker, 2010 and O. brevicaudatus Chu, Wu and Jin, 1981 ), but O. alleni has 3 POP (vs. 2 in O. vietnamensis sp. nov.) and a smaller eye diameter (10.6 in HL vs 8.4); O. brevicaudatus , from China, has biserial vomerine teeth (vs. uniserial in O. vietnamensis sp. nov.), a shorter head length (9.3 in TL vs 8.6) and a longer head and trunk (1.25 in tail length vs. 1.28) ( Table 2).

Figures

Fig. 1. Ophicihthus vietnamensis sp. nov. (a). OIM-E.55769, holotype, 387 mm TL, fresh; (b, c). OIM-E.55768, paratype, 421 mm TL, fresh. A anus and D dorsal-fin origin.

Fig. 2 Lateral view of head (a), teeth on maxilla and palatal area (b) and mandible (c) of Ophichthus vietnamensis sp. nov., OIM-Fi.04600, holotype, 387 mm TL. IO-infraorbital pores, M-mandibular pores, POP-preopercular pores, SO- supraorbital pores, ST- supratemporal pore. Arrows indicate interorbital (left) and mid-supratemporal (right) pores.