Ophichthus olivaceus McCosker & Bogorodsky, 2020

Bogorodsky, Sergey V., Mal, Ahmad O. & Alpermann, Tilman J., 2020, Description of a new snake eel Ophichthus olivaceus (Teleostei: Anguilliformes Ophichthidae) from the Red Sea, Zootaxa 4750 (1), pp. 31-48 : 34-37

Ophichthus olivaceus McCosker & Bogorodsky , sp. nov.

Olivaceous snake eel

( Figs. 1–3 ; Table 1 )

Holotype. SMF 35878 [KAU17-4], 756 mm TL, Red Sea , Saudi Arabia, off Jizan, st3, 16°45’10.3’’N, 42°45’10.3’’E, 35–41 m, 25 January 2017, coll. S. V. Bogorodsky, A.O. Mal & M. Gabr.

Paratype. KAUMM 453 [KAU17-80], 741 mm TL, Red Sea , Saudi Arabia, off Jizan, st13, 16°42’09.0’’N, 42°23’10.7’’E, 52–63 m, 31 January 2017, coll. S . V. Bogorodsky, A.O. Mal & M. Gabr .

Diagnosis. A moderately elongate species of Ophichthus with: tail length 46.3–46.4%, head length 9.0–10.4%, and body depth at gill opening 3.6–4.2% of total length; dorsal-fin origin above middle of pectoral fin; pectoral fin rounded, elongate and well-developed; posterior nostril within upper lip, not visible externally; two minute barbels along upper lip, the first between anterior and posterior nostrils, the second beneath mid orbit; pores apparent, supraorbital pores 1 + 4, infraorbital pores 4 + 2, preopercular pores 5 + 3; teeth small, conical, uniserial on vomer and jaws; coloration dark tan with olivaceous hue dorsally and laterally, tan ventrally on tail and pale yellow ventrally on trunk ( Fig. 1 ); two pale yellow smudges above pectoral-fin base; snout and lower jaw dark brown; throat pale orange-yellow, preopercle pale yellow and postorbital area pale yellow with numerous dark brown dots; dorsal fin olivaceous, anal fin pale olivaceous; tip of tail dark red; total vertebrae 141–145, mean vertebral formula 12–67.5–143.

Counts and measurements (in mm) of holotype and paratype (in parentheses). Total length 756 (741); head 68.2 (77.2); trunk 337 (321); tail 351 (343); predorsal distance 87.6 (101.5); pectoral-fin length 24.7 (29.1); pectoral-fin base 8.9 (7.3); body depth ca. 27 (31) at gill openings; body width ca. 32 (29) at gill openings; body depth at anus ca. 32 (29); body width at anus ca. 32 (29); body depth at branchial basket 33 (38); snout 15.3 (15.3); tip of snout to rictus 22.5 (21.5); snout overhang beyond tip of lower jaw 5.7 (5.2); eye diameter 7.2 (7.4); interorbital width 14.8 (16.2); gill opening height 9.9 (10.8); isthmus width 21.5 (21.5). Vertebral formula 11–69–145 (13–66–141).

Description. Body moderately elongate, subcircular to posterior third of tail, then becoming more compressed, its depth at gill openings 24–28 in TL. Branchial basket moderately expanded. Head length 4.2–4.9 in trunk length. Head and trunk 1.8–1.9, head length 9.6–11.1, and tail length 2.2 in TL. Snout rounded, moderately acute when viewed from above; a short groove bisecting underside of snout from the mid-base of anterior nostril tube. Upper jaw overhanging, snout tip extends forward by diameter of orbit. Upper jaw not elongated, rictus behind a vertical from posterior margin of eye by diameter of eye. Eye not enlarged, 2.9–3.1 in upper jaw and 6.8–9.4 in head. A shallow groove along interorbital region from snout to nape. Anterior nostrils tubular, not elongate, extending ventrolaterally from snout at ca. 30 o, reaching snout tip and chin when directed to them. Posterior nostril opening medially directed in upper lip, not visible externally. Two minute barbels along lower edge of lip of upper jaw, the first between the anterior and posterior nostrils, the second below mid-orbit. Dorsal-fin origin begins above middle of pectoral fin, predorsal length 7.3–8.6 in TL. Median fins obvious, not set in shallow grooves, slightly elevated and moderate in height anteriorly, then notably elevated approximately one-half head length prior to the tail tip, then diminishing in height approximately a snout length in advance of the pointed tail tip. Pectoral fins elongate, not lanceolate, the longest rays in dorsal third. Length of pectoral fins 2.7–2.8 in head length, 26–31 in total length. Gill openings about twice in isthmus width, from mid-body to below pectoral-fin bases, its upper edge opposite upper pectoral-fin rays. Head pores apparent ( Figs. 1 & 2 ). Single median interorbital and temporal pores. Supraorbital pores 1 + 4, infraorbital pores 4 + 2, lower jaw pores 5, preopercular pores 3, supratemporal pores 3. Faint rows of sensory papillae visible along the nape. Lateral-line pores apparent: 9 before gill opening in an arching sequence, 71 before mid-anus, total 147 pores. The last pore before the tail tip in a distance a little greater than eye diameter.

Teeth small, conical, uniserial, slightly retrorse and not close-set ( Fig. 3 ). One medial followed by 2 teeth medially and 2 laterally at tip of snout, followed by an intermaxillary rosette of 2 medial and 2 lateral irregular pairs of teeth, followed by a gap, then a single row of 12 small vomerine teeth, decreasing in size posteriorly. Maxilla with 9–10 uniserial teeth on each side. Lower jaw with 11–12 teeth in a single row.

Color when fresh ( Fig. 1 ). Coloration dark tan with olivaceous hue dorsally and laterally, tan ventrally on tail and pale yellow ventrally on trunk; two pale yellow blotches, one above another, above pectoral-fin base; head with dark brown snout and lower jaw, throat pale orange-yellow, preopercle pale yellow, and postorbital area densely dotted with dark brown; cephalic pores black-edged; anterior nostril yellowish suffused with dark brown; dorsal fin uniform olivaceous, anal fin uniform pale olivaceous, expanded part of both fins at tip of tail dark olivaceous; tail at its tip brownish, tip dark red; pectoral fins brown.

Coloration in ethanol uniform gray-brown dorsally, becoming paler along flanks and white ventrally. Snout, lower jaw, anterior nostrils, palate, and nape dark gray. Cheeks are light gray. Cephalic pores within dark spots. Lateral-line pores within minute pale spots. Anal fin and anal opening white like ventral surface. Dorsal fin pale gray becoming white at margin. Base of caudal fin black dorsally and ventrally about a snout’s length before pale tail tip. Pectoral fin gray, slightly darker in center, its margin pale. Two pale eye-sized blotches above pectoral, one above the dorsal insertion of the fin, the second above and slightly in advance of it and in line with orbit.

Size. The largest known specimen is 756 mm TL, a ripe female with packed ovaries, the ova ~ 1 mm in diameter. The paratype is 741 mm TL, also a ripe female with densely packed ovaries and ova ~ 1mm in diameter.

Etymology. From Latin, in reference to its coloration.

Distribution. Known from the holotype and paratype, trawled from a soft substratum from 35–63 m depth off Jizan, southern Saudi Arabia. At this point it is considered a Red Sea endemic.

Remarks. The new species differs from the majority of its congeners in having its anal-fin origin behind midbody and in having fewer total vertebrae. It is most similar in its morphology and meristics to Ophichthus echeloides ( D’Ancona 1928) from the Red Sea, and to Ophichthus oligosteus Hibino, McCosker & Tashiro 2019 from Tosa Bay, Kochi, Japan ( Hibino et al. 2019a). Ophichthus echeloides was described as Leptocephalus echeloides based on a leptocephalus captured in 1923 at 276 m depth near Perim (= Barim) Island, located near the intersection of the Red Sea and the Gulf of Aden. It had the characteristics of an ophichthid, however, no one was able to assign it to a described species. An adult Ophichthus was captured in 1989 by a trammel net at 300 m off Eilat, in the Red Sea.

It was subsequently recognized as a species of Ophichthus and the adult of Leptocephalus echeloides ( McCosker et al. 1993) . We are unaware of subsequent specimens. It is similar to the new species in its general appearance and its dorsal-fin origin (above middle of pectoral fin), and in possessing a third preopercular pore. It differs from it in its dentition ( O. olivaceus sp. nov. has few and uniserial teeth vs. O. echeloides which has many and biserial teeth in its jaws); its higher vertebral number (141–145 total, mean vertebral formula 14–68–143 vs. vertebral formula 11–50–125); shorter tail length (2.15 in TL vs. 1.7 in TL); and a shorter head (9.6–11.1 in TL vs. 8.4 in TL). The new species is also similar to O. oligosteus , a recently described Japanese congener, in its general appearance and head length ( O. oligosteus is 10.3 in TL), but differs in its dentition ( O. olivaceus sp. nov. has few and uniserial teeth vs. O. oligosteus which has more teeth in its jaws, and biserial maxillary and uniserial mandibular teeth); in the slightly anterior dorsal-fin origin (above mid pectoral fin vs. slightly behind the pectoral-fin tip); its higher vertebral number (141–145 total, mean vertebral formula 14–68–143 vs. vertebral formula 12–46–121); and its shorter tail length (2.15 times in TL vs. 1.6). Another species known from the Red Sea, O. erabo , shares a similar dentition (uniserial teeth in jaws and vomer) and vertebrae (143–155), but easily differs in having large brown spots (no spots in O. olivaceus sp. nov.), a longer tail (about 2 in TL vs. 2.15 in TL) and a shorter head (11.5–12.0 in TL vs. 9.6–11.1 in TL). The new species is similar genetically and also in its morphometry and meristics to Ophichthus lithinus ( Jordan & Richardson 1908), a medium-sized (to 148 cm TL) shallow sand and mud bottom species known from Taiwan, the Philippines, northern Australia, India, and Myanmar ( Ray et al. 2015; McCosker & Psomadakis 2018). This species has an elongate, cylindrical, tapering and laterally compressed body, a pointed snout and tail tip; a body depth behind gill openings of 32–37 in TL; its anus is at midbody; its head length is 9.7–11.7 in TL; it has uniserial dentition; a third preopercular pore; a notable barbel along the upper lip; and a similar pectoral-fin shape. Ophichthus lithinus has a vertebral formula of 12–67–152, with 147–157 total vertebrae. The species differ, however, in their coloration ( O. lithinus ’ head and body are brownish yellow, overlain dorsally by irregular brown saddles and mottling). In the original description of Leiuranus lithinus , Jordan & Richardson (1908) stated “dorsal inserted over middle of reflexed pectoral”; Ray et al. (2015) also reported the dorsal-fin origin to be above the middle of the pectoral fin. However, McCosker & Psomadakis (2018: 80), writing about a badly twisted Myanmar specimen wrote that the “dorsal fin arises ahead of gill opening by length of upper jaw”. A reexamination of that specimen demonstrates that its dorsal fin arises above the middle of its pectoral fin.

The new species is also similar in its morphometry and meristics to Ophichthus ishiyamorum McCosker 2010 , a deepwater species from the Gulf of Aden, Somalia, where it was trawled and trapped between 258– 400 m. Ophichthus ishiyamorum is similar in possessing a wedge-shaped pectoral fin, a dorsal-fin origin slightly in advance of the pectoral-fin tip, uniserial dentition, and a third preopercular pore. It differs from the new species in its body proportions (tail 52–55% and head 14–15% of TL) and vertebral number (MVF 15–50–131, total vertebrae 130–132).

Ophisurus apicalis Bennett 1830 was described from Sumatra in two lines of text and without an illustration. Nothing in its terse description could separate it from our new species as well as several other recognized taxa. The type specimen is lost. Data for the species are scarce, McCosker & Castle (1986) reported its tail length to be about 1.6 in TL and its total vertebrae 136–139; Kimura et al. (2018) did not provide the tail length but gave total vertebrae as 138–141. In addition, O. apicalis has biserial vomerine teeth. All three characters differentiate it from O. olivaceus . Y. Hibino is preparing an extensive description and history of the taxon and will be creating a neotype. Kimura et al. (2018), in additional to their five described species, briefly reported upon five unrecognized species from Vietnam. Their Ophichthus sp. 5 is very similar to O. olivaceus in having olivaceous coloration, but described it as having two rows of teeth on its vomer.

Molecular phylogenetics. The two specimens of Ophichthus olivaceus sp. nov. form a joint clade that is sister to a clade formed by two specimens of O. lithinus , both collected from the Western Pacific (i.e., Philippines and Taiwan, respectively, see Fig. 4 ). The two most closely related sequences of any specimen from each of the two clades are in average 0.015 nucleotide substitutions apart from each other, corresponding to a HKY distance value of 0.7 percent. The next higher nodes in the phylogeny did not receive substantial support from bootstrapped analyses, but together with 15 other sequences those from O. olivaceus and O. lithinus form a well-supported larger clade within the Ophichthinae . Most of these are also identified as members of Ophichthus by the respective sequence authors, but several sequence vouchers are identified as members of the genus Pisodonophis .

Figures

FIGURE 1. Ophichthus olivaceus sp. nov., SMF 35878 [KAU17-4], fresh holotype, 756 mm TL, off Jizan, Saudi Arabia, Red Sea. Photo by S.V. Bogorodsky.

FIGURE 2. Ophichthus olivaceus sp. nov., SMF 35878 [KAU17-4], holotype. A: underside of the head; B: head and anterior trunk close-up; C: cephalic sensory pores system; IO-infraorbital pores, LL-lateral line pores, M-lower jaw pores, PO-preopercular pores, SO-supraorbital pores, ST-supratemporal pores. Photos by S.V. Bogorodsky (A & B), drawing by J.E. McCosker (C).

FIGURE 3. Ophichthus olivaceus sp. nov., KAUMM 453 [KAU17-80], paratype, semi-diagrammatic illustration of the dentition. A: photograph of upper jaw; B: drawing of upper jaw (left) and lower jaw (right). Photo by S.V. Bogorodsky (A), drawing by J.E. McCosker (B).

FIGURE 4. Maximum Likelihood phylogenetic tree based on partial sequences (652 bp) of the mitochondrial COI gene includ- ing available sequences of Ophichthinae and COI barcoding sequences from the two type specimens of Ophichthus olivaceus sp. nov. and several sequences of the subfamily Myrophinae as the outgroup. Branches with 100 percent support from bootstrapped analyses (1.000 replicates) are depicted as broad lines, other bootstrap values higher than 50 percent are shown. Scale bar represents the average number of nucleotide nucleotide substitutions per site.