Opistognathus elizabethensis, Smith-Vaniz, 2004

Smith-Vaniz, William F., 2004, Descriptions of Six New Species of Jawfishes (Opistognathidae: Opistognathus) from Australia, Records of the Australian Museum 56 (2), pp. 209-224 : 216-218

Opistognathus elizabethensis n.sp.

Figs. 3D, 8; Tables 1–4

Opistognathus n.sp. ”.—Gill & Reader. 1992:220 (listed in annotated checklist of fishes collected at Middleton and Elizabeth Reefs).

Type material. HOLOTYPE: AMS I.27891-010, male (60.4), Elizabeth Reef, N side near lagoon entrance, 29°56'S 159°01'E, 0–5 m, explosives, D.M. Williams, et al., Dec. 1981 . PARATYPES: 3 specimens, 66.6–71.4 mm. AMS I.27891-048, gravid females (2, 66.6–70.8), same data as holotype; AMS I.27152-014, male (71.4), Elizabeth Reef, outer SW reef slope, 29°57'S 159°02'E, 15–18 m, A. Gill and S. Reader, 10 Dec. 1987 .

Diagnosis. A species of Opistognathus with dorsal fin XI, 18 or 19; body with about 47–51 oblique scale rows in longitudinal series, and scales absent anterolaterally forward of verticals from 6th or 7th dorsal-fin spine; dorsal fin with an oblong black spot (partially encircled by white border) between spines 3–6 that extends slightly onto dorsum; vomerine teeth 2 or 3.

Description. Dorsal-fin rays XI, 18–19. Anal-fin rays II, 17–19. Pectoral-fin rays 19–21. Caudal fin: procurrent rays 5–6+4–5, segmented rays 8+8, middle 13 or 14 branched, total elements 25 or 27; hypural 5 absent. Vertebrae: 10+23; last pleural rib on vertebra 10; epineural ribs 13–14.

Supraneurals absent, insertion pattern 0/0/1/1+1/1/. Gill rakers 8+16–17 = 24–25.

Scales absent on body anterolaterally forward of verticals from 6th or 7th dorsal-fin spines, and from head, nape, above and slightly below lateral line, pectoral-fin base, breast and anterior 1 3 of belly. Body with about 47–51 oblique scale rows in longitudinal series. Lateral-line terminus below verticals from 4th to 7th segmented dorsal-fin ray (total element position 15–18). Lateral line pores moderate, arranged in single series above and below embedded lateralline tubes. Cephalic sensory pores numerous, completely covering most of head, including all of predorsal area except a small area immediately adjacent to dorsal-fin origin; mandibular pore positions 1–3 occupied by relatively large, single pores, 4th position occupied by 1–3 pores, 5th position with 7–11 pores.

Anterior nostril about midway between posterior nostril and dorsal margin of upper lip, consisting of a raised tube with a short tentacle on posterior rim that when depressed does not reach or barely reaches margin of posterior nostril; height of tentacle about 0.5 to 1.0 times maximum diameter of posterior nostril. Dorsal fin moderately low anteriorly, gradually increasing in height posteriorly; profile relatively uniform with only a slight change in fin height at junction of spinous and segmented rays. Dorsal-fin spines moderately short and straight, not curved distally and without flexible tips; skin covering tips of spines with slightly swollen fleshy tabs; all segmented dorsal- and analfin rays branched distally. Outermost segmented pelvic-fin ray not tightly bound to adjacent ray, interradial membrane incised distally. Upper margin of opercle straight and slightly rounded posterodorsally; posterior margin of preopercle indistinct without a free margin. No papillae on inner surface of lips. Fifth cranial nerve passes under A1 section of adductor mandibulae.

Upper jaw not sexually dimorphic, extending 0.6 to 0.9 eye diameters behind posterior margin of orbit; maxilla widest at end and truncate, without flexible lamina posteriorly; supramaxilla small and terminally positioned. Jaws subequal, lower slightly included. Premaxilla with moderate conical teeth in outer row that become progressively smaller and more closely spaced posteriorly; 1 or 2 rows of much smaller inner teeth anteriorly, and 2 or 3 inner teeth on each side of premaxillary symphysis that are as large or larger than outer teeth and hooked backwards. Dentary with outer row of conical teeth (slightly smaller than outer, anterior premaxillary teeth) that are largest midlaterally; 2 inner rows of teeth (about same size as anterior outer row teeth) anteriorly, with most teeth in innermost row slightly canted backwards. Vomerine teeth 2 or 3. Infraorbital bones tubular, with wide openings for sensory canals ( Fig. 3D); 3rd infraorbital relatively robust and “L” shaped with a slight suborbital shelf.

Measurements of the 60.4 mm holotype (in parentheses) and 3 paratypes, 66.6–71.4 mm, as percentage of SL: predorsal length (29.5) 28.8–30.9; preanal length (58.6) 55.6–60.6; dorsal-fin base (68.5) 70.6–71.1; anal-fin base (37.7) 32.6–34.7; pelvic fin-length (20.0) 21.5–22.4; caudalfin length (19.7) 19.4–19.6; depth at anal-fin origin (15.6) 16.3–16.8; head length (31.6) 31.2–32.9; orbit diameter (8.5) 8.5–9.5; upper jaw length (18.4) 17.2–18.0. As percentage of head length: postorbital head length (64.7) 63.0–66.4; upper jaw length (58.1) 52.3–57.6; postorbital jaw length (20.2) 16.2–25.3; orbit diameter (27.0) 27.3–28.8.

Preserved coloration. Head and body uniformly tan; inner lining of maxilla and adjacent membranes dark brown, and a dark diagonal blotch externally on upper jaw positioned at rictus of mouth; dorsal fin with an oblong black spot between spines 3–6, encircled by narrow white border and extending slightly onto dorsum; remainder of fin with a very narrow pale basal stripe extending length of fin and bordered, in succession, by a narrow dark stripe, another pale stripe (in the largest paratype consisting of a row of narrowly connected white spots, each of which is centred on a fin ray), bordered above by dark pigment; tips of dorsalfin spines with swollen fleshy pads that are mostly dark (these structures pale or white in O. alleni and O. seminudus ); anal fin with a narrow pale basal stripe bordered by a narrower dark stripe, remainder of fin mostly uniform brown; pectoral fins immaculate; caudal fin pale dusky, and pelvic fins dark brownish, darkest on interradial membranes. In the largest paratype the pelvic and anal fins are almost uniformly black, and the belly noticeably dark. This specimens also differs from the others in having a small pair of widely separated, pale, basicaudal spots; these spots perhaps more noticeable owing to the darker caudal fin of this specimen.

Live coloration (A.C. Gill, pers. comm.): body yellowishbrown and pale markings in dorsal fin blue.

Etymology. The specific epithet refers to the type locality. If not an Elizabeth Reef endemic, this species likely occurs only at Elizabeth and the adjacent Middleton Reef (see below).

Distribution. Known only from Elizabeth Reef, where collected between 0–18 m, but possibly also present at the adjacent Middleton Reef (29°30'S 159°12'E). These two coral capped, volcanic seamounts, located about 500 km off Coffs Harbour, NSW, Australia, represent the southernmost coral atolls in the world (Slater & Phipps, 1977). Francis (1993) noted that the relatively young Lord Howe Island (6.9–6.4 million years B.P.) and Elizabeth and Middleton Reefs share a large number of species and probably should be treated as a single biogeographic unit. Lord Howe Island (31°33'S 159°4'E), Elizabeth and Middleton Reefs are only three of more than 20 known volcanic peaks in the Tasman Sea (Slater & Goodwin, 1973) that form parallel north-south chains along the western margin of the Lord Howe Rise and the trough between Lord Howe Rise and Australia. Although these three peaks are the only ones presently at or above sea level, their faunas may have been derived from older, now submerged, structures.