Apterichtus nariculus, Hibino, Yusuke, 2015

Hibino, Yusuke, 2015, A review of the finless snake eels of the genus Apterichtus (Anguilliformes: Ophichthidae), with the description of five new species, Zootaxa 3941 (1), pp. 49-78 : 73-75

Apterichtus nariculus n. sp.

Figures 15–16 , Table 1

Holotype. BPBM 38368, 308 mm TL, sex unknown, Laha (NW side of Ambon Bay), Ambon Island, Molucca Islands, Indonesia, depth 28–30 m, sand bottom, collected by J. Friedman and R.M. Pyle, 14 March 1995.

Diagnosis. An elongate species with: tail 1.8, head 16, and body depth 60 in total length; 3 preopercular pores and 5 pores in supratemporal canal; teeth conical, uniserial on jaws; one pair on vomer; anterior nostril non-tubular, flush with underside of snout; body mostly pale in preservative, few pale brown spots on head, the diameter less than eye diameter; and preanal vertebrae 60, total 137.

Counts and measurements (in mm) of the holotype. Total length 308; head 19.4; trunk 123.4; tail 165.5; body depth at gill openings 5.2; body width at gill openings 4.1; body depth at anus 4.7; body width at anus 4.3; head depth at branchial basket 5.9; head width at branchial basket 5.4; snout length 2.6; tip of snout to rictus 6.7; tip of snout to tip of lower jaw 3.3; eye diameter 1.7; interorbital distance 0.7; gill-opening length 2.4; isthmus width 0.9. Vertebral formula 60-137. Preanal lateral-line pores 62, 7 pores in branchial region.

Description. Body elongate, subcylindrical throughout, weakly keel-shaped dorsally, snout and tail tip sharply pointed; depth at gill openings 60 in TL. Branchial basket slightly wider and deeper than body. Head and trunk 2.2 in TL; head 16 in TL, 6.4 in trunk. Snout pointed, short, equal to 1.5 times eye diameter; an extremely short median groove ventrally on snout, reaching beyond anterior edge of posterior nostril. Slope of dorsal surface of snout approximately 40° relative to underside of snout. Lower jaw included, its tip located beneath anterior 1/4th of eye; snout extends beyond tip of lower jaw, distance from snout tip to tip of lower jaw almost equal to twice eye diameter; upper and lower lips meet when mouth is closed. Mouth moderately elongate. Rictus well behind rear margin of eye. Edge of upper lip smooth, a distinct crease extending from posterior margin of posterior nostril to end of rictus; a crease on lower lip same as upper, extending from middle of lower jaw to end of rictus. Eye developed, 3.9 in upper jaw and 11 in head, its anterior margin slightly before tip of lower jaw, its center in advance of middle of upper jaw. Anterior nostril non-tubular, a small hole with a pair of small flaps, located at anterior third of snout, invisible from above. Posterior nostril opens in outer lip beneath anterior margin of eye. Branchial openings low, ventral; branchial region modestly expanded, creating a bulbous region in posterior half of head. All fins absent.

Head pores ( Fig. 15 ) extremely small but apparent. Single median interorbital and temporal pores. Supraorbital pores 1+6, infraorbital pores 5 + 5, supratemporal pores 5, lower jaw pores 4 (5 on right side), preopercular pores 3. Lateral-line pores before anus 62, 7 pores in branchial region, almost complete except for near tip of tail.

Teeth ( Fig. 16 ) small, conical and slightly recurved posteriorly. Intermaxillary with a chevron of 5 teeth (the largest in the jaw), followed by a short gap and one pair of small vomerine teeth. Jaw teeth uniserial, small, 16–17 teeth on each side of upper jaw and 14–17 (some teeth lost) teeth on each side of lower jaw.

Coloration when fresh unknown. In alcohol preservative, body mostly pale, with pale brown spots on head, 4 spots arranged regularly on lower jaw; sizes of all spots less than eye diameter.

Size. A single specimen, the holotype, which is 308 mm TL, sex unknown.

Etymology. Named nariculus , in reference to its minute anterior nostrils.

Distribution. Known only from the holotype which was captured from Ambon, Indonesia, at 28–30m depth over a sand bottom.

Remarks. As mentioned previously, Apterichtus nariculus is similar to A. jeffwilliamsi in the shape of its anterior nostril. This new species differs from the latter in having a more obtuse and shorter snout (profile is 40° vs. ca. 30°, length is less than twice eye diameter vs. equal to or more than twice eye diameter), a longer trunk (40.0% vs. 35.0–36.2% of TL), fewer preopercular pores (3 vs. 4), and in its body coloration in preservative (few spots on head vs. numerous small spots on head and breast). Apterichtus nariculus also resembles A. klazingai in the shape of its snout, its preopercular and supratemporal pore counts, and in having 130–145 vertebrae. However, the former can be distinguished from the latter by the shape of its anterior nostril (hole vs. tube), its shorter head (6.3% vs. 7.1–8.3% of TL), and having slightly more vomerine teeth (2 vs. 0–1).

Figures

FIGURE 15. Head of holotype of Apterichtus nariculus, BPBM 38368, 308 mm. Drawn by Y. Hibino.

FIGURE 16. Dentition of holotype of Apterichtus nariculus, BPBM 38368, 308 mm. Drawn by Y. Hibino.