Ophichthus cuulongensis Vo, Hibino & Ho, 2025

Vo, Quang Van, Hibino, Yusuke, Ho, Hsuan-Ching, Le, Thao Thu Thi & Seah, Ying Giat, 2025, Two new snake eels (Anguilliformes, Ophichthidae, Ophichthus) from Viet Nam, with redescriptions of O. macrochir (Bleeker) and O. rutidoderma (Bleeker), ZooKeys 1231, pp. 311-329 : 311-329

Ophichthus cuulongensis Vo, Hibino & Ho sp. nov.

Figs 1 , 2 , Tables 1 , 2 English name: Mekong’s Estuary Snake Eel Vietnamese name: Ca ́ li ̣ ch mơ ̃

Type material.

Holotype: • OIM-E.55819 , 904 mm TL, ripe female, field no. Q. 01020, ca 12°19'N, 109°20'E, Đồng Hòa , Cần Giơ ̀, Hồ Chi Minh city, southeast coast of Vietnam, South China Sea, bottom trawl, ca 10–20 m, 28 Aug. 2023 . Paratypes: • Fifty seven specimens, 475–998 mm TL, all collected from some sites, including Đô ̀ng Ho ̀a port fishing (10°22'57.45"N, 106°53'0.91"E), Câ ̀n Giơ ̀ district, Hô ̀ Chi ́ Minh city and Tân Bi ̀nh market (ca 10°0'14.77"N, 106°37'23.73"E) and the old Ba Tri market (ca 10°2'25.96"N, 106°35'38.87"E), Ba Tri district and the Khâu Băng market (ca 9°49'33.35"N, 106°36'3.37"E), Tha ̣nh Phu ́ district, Bến Tre province: NMMB-P 41234 , 14 specimens, 640–831 mm TL, collected in 2020, 2023 & 2024 • OIM-E.55812 , 945 mm TL, 13 Nov. 2013 • OIM-E.55813 , 475 mm TL, 16 Sep. 2014 • OIM-E.55814 , 783 mm TL, 13 Nov. 2014 • OIM-E.55815 , 586 mm TL, 16 Sep. 2014 • OIM-E.55816 , 880 mm TL, 10 Sep. 2016 • OIM-E.55817 , 7 specimens, 640–872 mm TL, 06 & 08 Sep. 2020 • OIM-E.55818 , 2 specimens, 710–725 mm TL, 22 Jun. 2023 • OIM-E.55820 , 2 specimens, 696–781 mm TL, 20 Sep. 2023 • OIM-E.55821 , 8 specimens, 732–878 mm TL, 23 Sep. 2023 • OIM-E.55822 , 673 mm TL, 12 Oct. 2023 • OIM-E.55823 , 2 specimens, 640–688 mm TL, 15 Oct. 2023 • OIM-E.55824 , 10 specimens, 544–994 mm TL, 10 & 12 Nov. 2023 • OIM-E.55825 , 2 specimens, 784–810 mm TL, 19 Jan. 2024. KMNH VR 100622 , 4 specimens, 625–830 mm TL, collected in 2020 & 2023.

Diagnosis.

An extremely elongate snake eel species of the genus Ophichthus with the following combination of characters: occipital not convex prominently, dorsal of snout with median shallow groove, reaching to interorbital pore; three or more shallow wrinkles (usually 3) on posterior part of eye; body with numerous longitudinal wrinkles, also prominent on abdomen; head length 5.2–6.2 % TL; tail length 65.4–68.8 % TL; two protrusions along upper lip from each side (some paratypes 1 on one side); dorsal-fin origin slightly behind pectoral-fin tip; SO 1 + 3, POM 5 (or rarely 6) + 2; teeth small (but larger in intermaxillary and anterior vomer); body dark brown, abdomen generally paler; dorsal fin with dark margin entirely, anal fin initially pale but in posterior part with faded dark margin, the area more than two head length; total vertebrae 199–207, MVF 14-62 - 202.

Description.

Counts and measurements of the holotype (in mm). Total length 904, head 52.7, trunk 246.3, tail 605, predorsal length 73.1, pectoral-fin length 13.6; body depth at gill opening 16.2; body width at gill opening 13.0; body depth at anus 16.5; body width at anus 16.3; snout 7.2; upper jaw 13.6; snout overhang beyond tip of lower jaw 3.0; eye diameter 3.6; interorbital width 6.7; gill opening height 6.9; isthmus width 10.2.

Body extremely elongate (Fig. 1 a ), subcircular to posterior portion of tail, then becoming slightly compressed, its depth at gill openings 62 (55–69) in TL. Branchial basket slightly expanded and deeper than trunk. Skin slightly wrinkled behind eye, nape, and body with numerous longitudinal wrinkles, also prominent on abdomen. Head short 17.6 (16.1–19.2) in TL and tail elongate 1.5 in TL. Snout short 7.0 (6.4–8.0), tip broadly conical at dorsal view, and bisected by a median shallow groove; lower jaw included, its tip extending slightly beyond posterior margin of anterior nostril tube; its length 4.6 (4.3–5.3) in HL. Upper jaw moderately long, rictus well behind posterior margin of eye; its length 4.0 (3.8–4.3) in HL.

Eye moderate, at mid of upper jaw, its diameter 3.2 (2.8–3.8) in upper-jaw length and 14.8 (13.1–16.8) in HL. 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 large flap that extends well below edge of mouth gape. Two barbels on upper lip (rarely 1 on one side). Dorsal-fin origin behind head, less than one pectoral-fin length behind fin tip and 1.4 (1.2–1.6) HL behind head. Median fins low but obvious, ending approximately one snout length before broadly pointed tail tip. Pectoral fin with narrow base, its length less than three times its base width, broad at middle, the longest rays at mid-fin.

Head pores small but apparent (Fig. 2 a ). SO 1 (ethmoid) + 3 on dorsal surface of snout and interorbital space; IO 3 + 3, one between nostrils, two below eye, and three behind eye; M 5 (1 paratype with 6 on left side), the last pore slightly before rictus; POP 2, F 1, ST 3. Indistinct minute sensory papillae present along nape, anterior margin of orbit, and around base of anterior nostril. Lateral-line pores apparent; HLL 9 (8–10), in an arching sequence, PDLL 15 (13–17; PALL 63 (62–65); TLL 198 (195–202), the last at approximately an upper-jaw length in front of tail tip.

Teeth (Figs 2 b, c ) moderately large, conical, and variable sizes. Intermaxillary with 4–6 teeth large and robust, arranged in two rows (some paratypes with a one at center), followed by 19 (17–20) teeth on vomer, biserial rows (some paratypes with 3 irregular rows and uniserial posteriorly), which decrease slightly in size posteriorly. Maxilla with 18–21 (right side) or 17–22 (left side) teeth mostly triserial (some paratypes biserial at anterior portion). Mandible with 17–24 teeth on right side or 18–25 teeth on left side; teeth arranged in two or three well-separated rows anteriorly, gradually becoming two rows at middle then three rows posteriorly, outer row slightly larger and more robust than the inner row (Fig. 2 c ).

Coloration.

When fresh (Fig. 1 a ) body dark brown; pale white ventrally; dorsal fin dark margin; anal fin initially pale but in posterior part with faded dark margin, the area longer than two times head length; tail tip darker; pectoral fin pale to light yellow. After preservation, body uniformly dark brown dorsally and pale brown ventrally. Snout relatively darker than other skin; branchial basket and chest darker. Dorsal fin dark with dark margin; anal fin pale anteriorly and slightly blackish toward tail tip. Pectoral fin mostly pale with scattered dark grayish pigment on base. Mouth cavity pale with gray peppered dots. Peritoneum pale with gray peppered dots on upper half; stomach and intestine pale.

Size.

The two largest specimens (998, 945 mm TL) are both ripe females with loose eggs.

Etymology.

The specific name is derived from the Mekong River’s estuary. In Vietnamese, the name “ cư ̉ u long ” means nine dragons, which is the dragon’s mouth that waters flow from to the southern sea of Viet Nam.

Distribution.

Only known from the type series collected in Mekong’s estuary waters, southeast coast of Viet Nam, catching by bottom trawls and scoop net (push net); they are common in the waters. The depth range is estimated to be 8– 20 m.

Comparisons.

Ophichthus cuulongensis sp. nov. is similar to several of its congeners in their extremely elongated bodies. The selected characters for comparing these species are listed in Table 2 . Compared to those species, O. cuulongensis sp. nov. has distinct vertebrae count ranging 199–207 in total. It readily differs from O. nguyenorum sp. nov. (190–196), O. microcephalus (214), and O. rotundus (178–184). Moreover, the new species differs from O. congroides , O. chilkensis , and O. macrochir in having fewer supraorbital pores (4 = 1 + 3, vs 5 = 1 + 4) and body coloration.

Ophichthus cuulongensis sp. nov. is most similar to O. rutidoderma , both sharing a short head, relatively long tail, body depth at anus and pores on head and lateral line. However, it can be distinguished from O. rutidoderma by its MVF 14-62 - 202 (vs 15-63 - 197), a higher total vertebral count (199–207, vs 195–199), maxillary teeth (mostly biserial or more vs uniserial anteriorly and biserial posteriorly), and mandible teeth (biserial to triserial vs biserial anteriorly and uniserial posteriorly).

Ophichthus cuulongensis sp. nov. is also similar to O. chilkensis and O. macrochir , sharing a short head, a relatively long tail, an anus situated at the front of the total length, preopercuomandibular pores, and numerous longitudinal wrinkles on the body. However, it can be separated by its MVF 14-62 - 202 (vs 11-69 - 210 and 12-69 - 214, respectively), fewer total vertebrae (199–207, vs 206–214 and 207–221, respectively), and a shorter upper-jaw length (3.8–4.3 in HL, vs 3.2–3.8 and 2.4–3.6 in HL, respectively).

Although Ophichthus cuulongensis sp. nov. shares similar vertebral counts and preoperculomandibular pores with O. congroides , the former can be separated from the latter by having fewer lateral-line pores before anus (62–65 vs 78) and a shorter head length (5.2–6.2 % TL, vs 8.3–8.4 % TL) and a shorter snout length (6.5–7.8 in HL, vs 4.9–5.1 in HL) and a shorter upper-jaw length (3.8–4.3 in HL, vs 2.3 in HL) and different MVF (14-62 - 202 vs 21-76 - 206).

Remarks.

Ophichthus cuulongensis sp. nov. has some characteristics, such as tooth arrangement and the shape of protrusions, which may be caused by ontogenetic changes. The jaws are arranged in biserial and triserial rows; vomerine teeth also show variability in arrangement among materials we examined. The teeth are large and robust to fat, becoming subequal anteriorly, similar to the teeth form of Pisodonophis in the larger specimens. The protrusions usually number two, but the one can degenerate or become very small on the side lip.

Figures

Figure 1. Ophichthus cuulongensis sp. nov., holotype, OIM-E. 55819, 904 mm TL a fresh specimen, arrows point to the DFO and AFO, respectively b close-up of head view from lateral side, arrow points to the DFO c close-up of head view from dorsal.

Figure 2. Drawing demonstrating the head pores (a) and teeth on both jaw (b, c) of Ophichthus cuulongensis sp. nov. a, b from the holotype c from OIM-E. 55824, paratype, 808 mm TL.