Apterichtus australis, John E. McCosker & John E. Randall, 2005

John E. McCosker & John E. Randall, 2005, Notes on the snake eels of the genera Apterichtus and Ichthyapus (Anguilliformes: Ophichthidae) of the Central and South Pacific, with the description of a new species., Zootaxa 800, pp. 1-11 : 2-6

Apterichtus australis sp. nov.

(Pl. 1a; Figs. 1-2; Tables 1-2)

Apterichtus flavicaudus (non Snyder): Randall et al. 1990:7.

Holotype: BPBM 12306, 395 mm total length, sex undetermined, Rapa, off Hiri Bay (27°36'S, 144°18'W), depth 30 m, captured over coarse sand adjacent to a reef using rotenone by J.E. Randall and D. Cannoy, 10 February 1971.

Paratypes: BPBM 39455, 3(297-400 mm) ; CAS 219463, 358 mm ; and USNM 376606, 327.5 mm; collected with the holotype . BPBM 11842, 351 mm, Pitcairn Island, 2 km northwest of Pitcairn Island, depth 88-100 m, dredge, D. M. Devaney, 19 October 1967 . BPBM 16896, 2(294-382 mm), Pitcairn Island, depth 40-45 m, patch reef and adjacent sand, rotenone, J. E. Randall et al., 6 January 1971 . BPBM 16506, 2(137-326 mm), Oeno Island, Pitcairn Group, north side of atoll, depth 12-18 m, reef and adjacent sand including a cave, rotenone, J. E. Randall et al, 18 December 1970 . ZMUC P32853, 291.5 mm, Raoul Island, Kermadec Islands (29°13'S, 177°57'W), depth 75-85 m, dredge, Galathea Expedition Sta. no. 674, 3 March 1952 . BPBM 30548, 2(245-371 mm), Easter Island, off east end of Anakena, depth 20 m, sand and isolated rock with coral, collected by J.E. Randall and L.H. DiSalvo, 14 February 1985 .

Diagnosis. An elongate, finless species of sphagebranchin ophichthine (sensu McCosker 1977) with: tail 45-57% and head 5-5.5% of total length; 3 preopercular pores and 3 pores in supratemporal canal; teeth conical, uniserial on jaws and vomer; body mostly pale in preservative, creamy dorsally and reddish-brown ventrally with light and dark head markings in life; and mean vertebral formula 82-164, total vertebrae 162-167.

Counts and Measurements of Holotype (in mm). Total length 395; head 19.9; trunk 195.1; tail 180; body depth at gill openings 5.4; body width at gill openings 4.7; body depth at anus 4.5; body width at anus 4.5; snout 4.0; tip of snout to rictus 7.0; eye diameter 1.2; interorbital distance 2.0; gill opening length 1.9; isthmus width 0.9. Vertebral formula 85-164. Lateral-line pores 164, 6 in branchial region, 87 pores before the anus.

Description of the Holotype. Body elongate, nearly cylindrical throughout, snout and tail tip pointed (Pl. 1a), depth at gill openings 71 in TL. Branchial basket slightly wider and deeper than body. Head and trunk 1.8 in TL; head 20 in TL, 9.8 in trunk. Snout pointed, its underside somewhat rounded and bisected by a groove (Figs. 1-2). Lower jaw included, its tip slightly in advance of eye; upper and lower lips meet when mouth is closed. Mouth moderately elongate. Rictus well behind rear margin of eye. An obvious crease extends posteriorly in upper lip from beneath eye to rictus. Eye moderately developed, 6 in upper jaw and 17 in head, its center above middle of upper jaw. Anterior nostril within an elongate tube, approximately 1/2 the diameter of the eye, its base about midsnout and anterolaterally directed when viewed 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.

Head pores (Fig. 1) conspicuous. Single median interorbital and temporal pores. Supraorbital pores 1 + 4, infraorbital pores 5 + 2, supratemporal pores 3, lower jaw pores 4, preopercular pores 3. (The head pores of the 12 paratypes are identical to those of the holotype, save 1 aberrant specimen which has 6 rather than 3 temporal pores.) 164 lateralline pores, 6 above branchial region, 87 before anus.

Teeth (Fig. 2) uniserial, small, conical and slightly recurved. Intermaxillary with a chevron of 5 teeth (the largest in the jaw), followed by a short gap and a linear row of 5 small vomerine teeth. Jaw teeth nearly subequal, small, 9-10 teeth in each side of upper jaw and 9-10 teeth in each side of lower jaw.

Body mostly colorless in isopropanol. Notes made by the junior author at the time of capture describe fresh specimens from Rapa and Pitcairn as being creamy white dorsally and reddish brown ventrally, with an irregular broad pale band running diagonally up and behind the eye from the corner of the mouth to a light reddish brown band behind it, and the anterior lateral-line pores are reddish. The body of the larger Easter Island specimen (Pl. 1a) is similarly colored, however it differs in that its head markings are markedly white, rather than pale, as is the condition of Rapa and Pitcairn specimens.

Size. The largest specimen examined is 400 mm, sex undetermined.

Etymology. Named australis in recognition of this species' distribution.

Distribution. Known from the south Pacific island groups of Rapa, Pitcairn, Easter and the Kermadecs. It was captured over sand with associated rock and coral reef bottoms using ichthyocides and dredges between 12-100 m depth.

Remarks. The new species differs from all of its known congeners in a combination of characters (see Table 2). In that species of Apterichtus are finless and typically pale in preservative, the most suitable characters for differentiation are vertebral numbers, cephalic pore number and location (particularly the preopercular and supratemporal series), and dentition. Apterichtus australis is most closely related to A. flavicaudus (Snyder 1904) (Pl. 1b), currently known from the Hawaiian Archipelago, Midway Island, southeastern Australia, and the Seychelles. Apterichtus flavicaudus occupies similar habitats and has been caught between 7 m and 293 m depth using rotenone and trawls, and has been captured at the surface beneath nightlights. They differ in their preanal vertebral number ( A. flavicaudus 73-80; A. australis 79-85), total vertebral number ( A. flavicaudus 154-166, MVF=78-158, n=17; A. australis 162-167, MVF=82-164, n=14), and dentition. Apterichtus australis has 5-6 vomerine teeth whereas A. flavicaudus has 1-2. All other described species of Apterichtus have fewer vertebrae, and several differ in the number and pattern of their cephalic pores. Undescribed species of Apterichtus exist in the eastern Pacific, Fiji and Vanuatu, the Marquesas, and Flores Island (McCosker, in preparation); however, they all have fewer vertebrae and differ in their cephalic pore conditions. Apterichtus keramanus Machida et al. (1997), described from a single Japanese specimen, has fewer vertebrae(122) and more numerous cephalic pores, and is probably not within Apterichtus .