Ophichthus nansen McCosker & Psomadakis, 2018

Psomadakis, Peter N., 2018, Snake eels of the genus Ophichthus (Anguilliformes: Ophichthidae) from Myanmar (Indian Ocean) with the description of two new species, Zootaxa 4526 (1), pp. 71-83 : 72-75

Ophichthus nansen McCosker & Psomadakis sp. nov.

New English name: Nansen’s snake eel (En)

( Figs. 1 – 3 )

Material examined. Holotype : USNM 438268 , 389 mm TL, a ripe male, off Ayeyarwady Delta , Myanmar (14 o 41.49 N, 95 o 29.32 E), R/ V Dr. Fridtjof Nansen, Sta. 88, bottom trawl, 103 – 106 m depth, 13 May 2015, collected by P. N. Psomadakis.

Diagnosis. A moderately elongate species of Ophichthus with: tail 62%, head 10.3%, and body depth at gill opening 3.4% of TL; dorsal-fin origin above mid-pectoral fin; pectoral fin elongate, but not filamentous, longer than upper jaw; posterior nostril a hole above upper lip, covered by a flap that extends to or below edge of mouth; barbels present behind anterior and posterior nostrils; eye large, its posterior margin in advance of rictus of jaw; pores small but conspicuous, SO 1 + 4, IO 4 + 2, POM 6 + 2; teeth small, close-set and conical, biserial on anterior vomer and jaws; coloration dark gray-brown, paler ventrally, pectoral and median fins black; vertebral formula 11- 53-146.

Counts and measurements of the holotype (in mm). Total length 389; head 39.9; trunk 109.1; tail 240; predorsal distance 47; pectoral-fin length 14; pectoral-fin base 3.5; body depth ca. 13.5 at gill openings; body width ca. 14 at gill openings; body depth at anus ca. 12.5; body width at anus ca. 12.5; body depth at branchial basket 18; body width at branchial basket ca. 14.5; snout 8.8; tip of snout to rictus 11.2; snout overhang beyond tip of lower jaw 2.2; eye diameter 3.4; interorbital width 5.2; gill opening height 5.5; isthmus width 9.7. Vertebral formula 11-53-146.

Description. Body moderately elongate ( Figure 1 ), subcircular to level of anus, then becoming more compressed, its depth at gill openings 29 in TL. Branchial basket moderately expanded. Head 2.7 in trunk. Head and trunk 2.6, head 9.7, and tail 1.6 in TL. Snout slightly rounded, moderately acute when viewed from above; a short groove bisecting underside of snout nearly to tip of upper jaw; snout, lips and chin densely covered with minute sensory papillae. Lower jaw included, its tip reaching anterior base of anterior nostril tube. Upper jaw not elongated, rictus behind a vertical from posterior margin of eye. Eye large, 3.3 in upper jaw and 11.7 in head. Anterior nostrils tubular, extending anteriorly from snout at ca. 30 o, 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 present along upper lip behind the anterior and posterior nostrils. The first and largest descending from upper lip behind the anterior nostril tube; the minute second barbel is beneath the anterior margin of the orbit. Dorsal-fin origin above mid-pectoral fin. Median fins low but obvious, ending in a shallow groove about an eye diameter before the sharply pointed tail tip. Pectoral fins longer than upper jaw, elongate and lanceolate, but not filamentous.

Head pores small but apparent ( Figure 2 ). Single median interorbital and temporal pores. Supraorbital pores 1 + 4, infraorbital pores 4 + 2, mandibular pores 6, preopercular pores 2, supratemporal pores 3. Faint rows of sensory papillae along the nape. Lateral-line pores minute but apparent; 10 before gill opening in a high arching sequence, ca. 40 before anus, ca. 110 total, the last ca. the distance of the snout from the tail tip.

Teeth ( Figure 3 ) small, close-set, slightly retrorse, conical but not sharp, and difficult to ascertain. Largest are the anteriormost central tooth and two on each side at tip of snout, followed by an intermaxillary rosette of about 5 irregular pairs of teeth, followed by a patch, 2-3 irregular pairs, and a single row of ca. 12 close-set vomerine teeth, decreasing in size posteriorly. Maxillary with about 8 pairs of subequal, irregularly biserial teeth followed by 10-12 uniserial teeth decreasing in size. Lower jaw with about 8-10 pairs of subequal, irregularly biserial teeth, followed by 10-12 smaller uniserial teeth.

Coloration in life as in Figure 1 . Coloration in ethanol uniform gray-brown, becoming paler in throat region and from mid-flanks to belly. Median fins black. Pectoral fins black, their margins pale. Edge of gill opening, anterior nostrils, and lip barbels pale. An irregular pattern of fine black specks equal in size to lateral-line pores along dorsal and ventral surface of trunk and tail. Inner margins of lips pale, with a fine black line extending from beyond eye to rictus. Median fins basally pale. Anterior nostrils, tail tip, anal opening, and peritoneum pale. Inside of mouth pale, tongue speckled with brown flecks.

Size. Known only from the holotype, a 389 mm TL male.

Etymology. Named after the EAF-Nansen Prorgramme and in honor of Dr. Fridtjof Nansen, the famous Norwegian explorer and scientist for whom the programme and research vessel were named. Since 1975, the EAF- Nansen Programme has contributed to increasing the knowledge of global marine biodiversity while supporting developing countries in fisheries research and sustainable management of their resources throughout surveys at sea and capacity building. The specific name is treated as a noun in apposition.

Distribution. Known only from the holotype, collected by bottom trawl at 103 – 106 m depth over a mud and muddy sand bottom.

Remarks. The holotype is a male with well-developed testes. The reduced facial pore and lateral-line pore conditions are typical adaptations to the sand and mud-burrowing behavior of some ophichthid species ( McCosker et. al. 2012).

The new species is most similar in morphology and appearance to that of Ophichthus aphotistos McCosker & Chen 2000 , a deepwater species from Japan and Taiwan, and to O. cruentifer (Goode & Bean, 1856) , a deepwater species from the NE Atlantic Ocean ( O. cruentifer data are from McCosker et. al. 1989: 384 – 386; Hibino et al. 2016 provided additional data for Japanese and Taiwanese O. aphotistos ). All three are similar in their proportions, pectoral-fin size and shape, biserial jaw dentition, faint sensory papillae, and dark body coloration. They differ somewhat in their body depth ( O. nansen 3.4% of TL, O. aphotistos 2.5 – 2.9%, and O. cruentifer 2.3 – 3.0%), dorsal-fin origin (above mid-pectoral fin, vs. pectoral-fin length behind gill openings, vs. pectoral-fin length behind gill openings), head length 10.3% of TL, vs. 7.7 – 8.7%, vs. 6.9 – 8.7%), and vertebral formulae (11-53-146 vs. 17-59- 160, vs. 16-57-149).

Figures

FIGURE 1. Ophichthus nansen McCosker & Psomadakis, sp. nov., holotype, USNM 438268, 389 mm TL, male. Photographed soon after capture and before preservation by P.N. Psomadakis. Arrows indicate the origins of the dorsal fin (left) and the anal fin (right).

FIGURE 2. Semi-diagrammatic illustration of left lateral head view of the holotype of Ophichthus nansen McCosker & Psomadakis, sp. nov. Drawn by J.E. McCosker.

FIGURE 3. Semi-diagrammatic illustration of the dentition of the holotype of Ophichthus nansen McCosker & Psomadakis, sp. nov. Drawn by J.E. McCosker.