Ophichthus multidentis Hibino, Ho & Huang, 2024

Hibino, Yusuke, Ho, Hsuan-Ching & Huang, Jian-Fu, 2024, Descriptions of two new dark-body snake eels of the genus Ophichthus (Anguilliformes, Ophichthidae) from Taiwan, ZooKeys 1220, pp. 63-78 : 63-78

Ophichthus multidentis Hibino, Ho & Huang sp. nov.

Figs 3 , 4 ; Tables 1 , 2

Material examined.

Holotype: NMMB-P 36205 , 433 mm TL, ca 22°42.5'N, 120°10.8'E, off Ke-tzu-liao , Kaohsiung, southwestern Taiwan, northern South China Sea, 4 Sep. 2019, collected by H.-C, Ho . Paratypes: Four specimens, all collected from Daxi fish landing port , 24°56.5'N, 121°54.0'E, northeastern Taiwan, southern East China Sea, collected by J.-F. Huang: TOU-AE 7802 , 519 mm TL, 25 July 2020; TOU-AE 8998 , 554 mm TL, TOU-AE 8999 , 597 mm TL, 28 Nov. 2022; TOU-AE 9294 , 696 mm TL, 9 Jan. 2023 .

Diagnosis.

An elongate Ophichthus with the following combination of characters: head 8.0–8.8 % TL; tail 56.8–58.8 % TL; dorsal-fin origin behind pectoral-fin tip by 3.0 times the pectoral fin length; no protrusions along upper lip; SO 1 + 3; POM 5 or 6 + 2; teeth on maxilla in 4 irregular rows or 5 rows anteriorly and 4 rows posteriorly, teeth on vomer in up to 4 rows, teeth on dentary in 4 rows anteriorly, 3 rows posteriorly; body uniformly dark with creamy white median fins; 22–26 predorsal and 63–65 preanal lateral-line pores; total vertebrae 162–164, MVF 24-64 - 163.

Description.

Counts and measurements are mostly shown in Tables 1 , 2 .

Body elongate, slender (Fig. 3 ), cylindrical, its depth at gill opening 13.1–18.4 (18.4 in holotype) in head and trunk, 30.5–44.7 (44.7 in holotype) in TL; tail weakly compressed, tapering slowly toward tip, its length 1.7–1.8 (1.7 in holotype) in TL; skin of body nearly smooth, with numerous extremely small longitudinal wrinkles ventrolaterally.

Head small, 4.9–5.2 (5.1 in holotype) in head and trunk and 11.3–12.6 (12.4 in holotype) in TL; dorsal contour of head relatively linear above eye, occipital weakly convex; branchial basket moderately swollen, maximum depth 3.2 in head. Snout relatively acute but bulbous, relatively long, 4.7–5.3 (4.9 in holotype) in HL; a dermal groove ventrally on snout. Anterior nostril tubular, towards anteriorly; opening with moderately expanded flap anteriorly; posterior nostril a hole at inner margin of upper lip, completely covered by a wide but low dermal flap. Eye moderate in size, 1.7–2.6 (2.4 in holotype) times in snout length. Mouth inferior, tip of lower jaw below middle of anterior nostril tube base; rictus slightly behind posterior margin of eye. Lips without any sensory papillae and protrusions; inside along base on anterior nostril tube with several small low hump arranged as a row. Interorbital region smooth, gently convex. Gill openings located ventrolaterally, upper ends slightly below insertion of pectoral fin.

Sensory pores on head (Fig. 4 A ) developed but very small and not obvious; SO 1 + 3, first (ethmoid pore) on underside of snout tip and 3 along dorsal surface of snout, the last above upper margin of eye; IO 3 + 3, 1 pore behind base of anterior nostril, 2 below eye, and 3 arranged in a vertical row behind eye; POM 5 or 6 + 2 (6 in holotype), last pore behind rictus; ST 3, 1 on mid-temporal; single interorbital pore. Lateral line nearly complete, ending by about 1 HL before tail tip; canal on branchial basket weakly arched, 8 on branchial basket before gill opening, 22–26 anterior to origin of dorsal fin, 63–65 anterior to anus, and total 145–148 (8, 24, 63 and 145 in holotype).

Teeth numerous, conical, pointed but shape and size variable (Fig. 4 B ); multiserial teeth on maxilla and dentary, outermost rows slightly larger and more robust than others, innermost teeth slender and more recurved posteriorly. Those on maxilla in 4 irregular rows in holotype, but in larger specimens ( TOU-AE 8999 and 9294) 5 rows anteriorly and 4 rows posteriorly; on dentary arranged in 4 rows anteriorly and 3 rows posteriorly; on vomer moderate in size, becoming smaller posteriorly, 4 rows maximum and decreasing to single row posteriorly; 6 or 7 (6 in holotype) large and robust, close-set teeth on intermaxillary, mostly concealed by lips.

Dorsal and anal fins low; ending slightly before tail tip; dorsal-fin origin well behind pectoral-fin tip by 2.3–3.5 (2.8 in holotype) times the pectoral-fin length; pectoral-fin tip pointed but not lanceolate; caudal fin absent.

Coloration.

Freshly caught specimen has a uniformly purplish to blackish brown body, pectoral fin dark gray, and dorsal and anal fins pale; tail tip pale (Fig. 4 A ). Preserved condition in 50 % isopropanol ethanol (Fig. 3 B ): head and body dark brown except pale anus and tail tip; lips relatively darker than other skin; branchial basket and chest darker; anterior nostril tube same as body color; sensory pores not prominently margined; mouth cavity various, completely creamy white or dusky anteriorly, completely dusky on inside of lower jaw in three specimens; membrane of gill opening paler than body; head partly faded with some pale patches possibly imprinted by fishing net; dorsal and anal fins creamy white without melanophores; pectoral fin dark brown.

Etymology.

The specific name is derived from the Latin multi (many) and dentes (teeth), referring to the diagnostic character of four tooth rows on jaws.

Comparison.

The tooth pattern of Ophichthus multidentis sp. nov. is unique among the congeners. It is the only member of Ophichthus that possesses up to 5 rows of small teeth on jaws and vomer in the northwestern Pacific region.

Ophichthus multidentis sp. nov. is similar to a number of species that have the dorsal-fin origin situated behind the head by more than twice the pectoral-fin length (or predorsal length more than 1.5 times head length) and no blackened anal-fin base in advance of tail tip ( Vo and Ho 2021: table 1; Ho et al. 2022). Ophichthus multidentis sp. nov. is most similar to Ophichthus longicorpus Vo & Ho, 2021 in having a uniformly dark body, dorsal-fin origin 3 times the pectoral-fin length behind the pectoral fin tip (cf. 3.4–5.7 times in O. longicorpus ), but differs in having more tooth rows on jaws and vomer (at least 4 irregular rows on maxilla and vomer vs mainly 2 rows on jaws and 2 or 3 rows anteriorly and uniserial posteriorly on vomer), a longer tail (56.8–58.8 % TL vs 50.0–52.9 % TL), and different vertebral formula (MVF 24-64 - 163 vs 27-68 - 159).

Ophichthus multidentis sp. nov. is also similar to O. aphotistos and O. kusanagi in having a uniformly colored body, similar vertebral counts and proportions of head length, tail length, and body depth. It differs from these species in having more predorsal vertebrae (23–26 vs 16–20 in O. aphotistos and 17–22 in O. kusanagi ), more numerous and smaller teeth on maxilla arranged irregularly in up to 5 rows (vs relatively few and large teeth, arranged in biserial or mostly biserial anteriorly) and fewer mandibular pores (5 or 6 vs 6) ( Hibino et al. 2016; Hibino et al. 2019 b; this study). We do not have the sufficient information of the molecular evidence of the new species with other congeners, while the partial sequence of O. multidens sp. nov. differs from O. aphotistos (S. Endo pers. comm.).

Figures

Figure 3. Ophichthus multidentis sp. nov., NMMB-P 36205, holotype, 433 mm TL, Ke-tzu-liao, Kaohsiung, Taiwan A fresh condition B preserved condition. Arrows indicate positions of dorsal-fin origin (lefts) and anus (rights).

Figure 4. Line drawings of O. multidentis sp. nov., NMMB-P 36205, holotype, 433 mm TL A sensory pores on head B teeth on upper (left) and lower jaws (right). Arrows indicate interorbital (left) and mid-temporal pores (right); black solid circles indicate holes of lost tooth; and broken lines indicate concealed teeth by fleshy lips.