Opistognathus seminudus, 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 : 213-214

Opistognathus seminudus n.sp.

Figs. 2B, 3B, 4B, 5, 6; Tables 1–4

Opistognathus sp. — Russell, 1983:107 (listed; Heron and One Tree islands).

Type material. HOLOTYPE: AMS I.22794-001, female (59.7), Australia, Great Barrier Reef , Capricorn Group , One Tree Island , reef flat at SW end of island, 0–1 m, V. G. Springer, 30 Nov. 1966, Sta. 66–13. P ARATYPES: 78 specimens, 17.7–86.2 mm, all from the Great Barrier Reef. Capricorn Group, One Tree Island : ANSP 142950 (8, 21.5– 73.7, 3 C&S) and USNM 220928 (14, 59.5–3.7), same data as holotype; AMS I.15641-042 (73.2), AMS I.15681-063 (4, 60.7–76.1), AMS I.17445-031 (9, 73.0–47.3), 3 m, F. Talbot, 19 Sep. 1968; AMS I.20201-028 (60.0), 0–2 m, D. Hoese, 29 Sep. 1971; AMS I.20212-004 (2, 50.9–85.5), 20 m, F. Talbot et al., 6 Oct. 1971; BPBM 14385 (3, 33.0– 70.5), 0.5–1.5 m, J.E. Randall, Jan. 1973; CAS 13790 (1, 72.4), 0.5 m, B.B. Collette and W.N. Eschmeyer, 22 Nov. 1969; CAS 13818 (3, 17.7–63.9), 6 m, F. Talbot et al., 26 Nov. 1969; USNM 220941 (26.6), 8–12 m, V. G. Springer, 7 Dec. 1966; USNM 220942 (67.8), 4 m, V. G. Springer, 1 Dec. 1966; USNM 220943 (9, 23.3–74.6), 5 m, V. G. Springer, 25 Nov. 1966; USNM 220944 (6, 61.0–77.4), 1 m, V. G. Springer, 27 Nov. 1966; and USNM 295803 (3, 80.3–86.2), 4.5 m, V. G. Springer, 11 Dec 1966. Capricorn Group, Wistari Reef: BPBM 14535 (54.0), 22 m, J.E. Randall, 22 Jan. 1973. Capricorn Group, Heron Island: AMS IB.4054–5 (2, 59.8–64.9), AMS I.15482-002 (48.6), H. Choat, 16 Jun. 1965; and USNM 295804 (64.9), H. Choat, 23 Feb. 1967. Gillett Cay: AMS IB.6126 (76.0), AMS IB.6127 (71.9), and AMS IB.6128 (3, 49.8–54.7), Swains Reef Expedition, Oct. 1962. Lizard Island: AMS I.20766- 010 (2, 54.5–57.7), D. Hoese et al., 6 Feb. 1975.

Diagnosis. A species of Opistognathus with dorsal fin XI (exceptionally X), 14–16; body with about 28–36 oblique scale rows in longitudinal series, and with scales absent anterolaterally forward of verticals from ultimate spine to 2nd segmented dorsal-fin ray; dorsal fin with conspicuous ocellus between spines 2–5; vomerine teeth 1–3.

Description. Dorsal-fin rays XI (exceptionally X), 14–16.

Anal-fin rays II, 14–15. Pectoral-fin rays 19–21. Caudal fin: procurrent rays 4–6+4–5, segmented rays 8+8, middle 12–14 branched, total elements 24–27; hypural 5 present.

Vertebrae: 10+18 (10+ 19 in one of 68 specimens); last pleural rib on vertebra 10; epineural ribs 12–15. Supraneurals absent, insertion pattern 0/0/1/1+1/1/. Gill rakers 8–10+16–18 = 24–27.

Scales absent on body anterolaterally forward of verticals from ultimate spine to 2nd segmented dorsal-fin ray, and from head, above lateral line, pectoral-fin base, breast and belly. Body with about 28–36 oblique scale rows in longitudinal series. Lateral-line terminus below verticals from 7th to 11th segmented dorsal-fin rays (total element position 18–22).

Lateral line pores numerous, arranged in multiple series along embedded lateral-line tubes. Cephalic sensory pores very numerous ( Fig. 6), in adults 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 with 4–10 pores, 5th position with 12–24.

Anterior nostril distinctly closer to posterior nostril than to dorsal margin of upper lip, and with a simple, flattened tentacle on posterior rim that when depressed usually reaches margin of orbit; height of tentacle about 1.5 to 2.0 times maximum diameter of posterior nostril. Dorsal fin very low anteriorly, gradually increasing in height posteriorly; profile relatively uniform with only a slight change in fin height at junction of last spine and anterior segmented rays. Dorsal-fin spines relatively short and straight, at most only slightly curved distally and without flexible tips; tips of spines with slightly swollen fleshy tabs; all segmented dorsal- and anal-fin rays branched distally or 1st anal ray unbranched. 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.

214 Records of the Australian Museum (2004) Vol. 56

Upper jaw slightly sexually dimorphic, extending 0.8 to 1.1 (ƋƋ) and 0.6–0.9 (♀♀) eye diameters behind posterior margin of orbit; maxilla widest at end and rounded, without flexible lamina posteriorly ( Fig. 2B); supramaxilla present, small and terminally positioned. Jaws subequal. Premaxilla with an outer row of stout conical teeth that become progressively smaller posteriorly; 1 or 2 inner rows of smaller conical teeth anteriorly, those nearest symphysis largest and usually canted backward. Dentary with an outer row of moderate teeth, largest midlaterally, extending ½ to 2 3 length of jaw, and an inner row of smaller conical teeth anteriorly that are usually strongly hooked backward. Vomerine teeth 1–3. Infraorbital bones tubular, with wide openings for sensory canals ( Fig. 3B); 3rd infraorbital relatively robust and “L” shaped with a slight suborbital shelf. Second pharyngobranchial rod-shaped with distal end greatly expanded ( Fig. 4B).

Measurements of the 59.7 mm female holotype (in parentheses) and 23 paratypes, 13 ƋƋ 57.9–86.2 mm and 10 ♀♀ 60.6–73.7 mm, as percentage of SL: predorsal length (30.9) 29.9–35.0; preanal length (58.6) 58.8–64.7; dorsalfin base (67.0) 62.9–70.1; anal-fin base (31.6) 29.4–35.4; pelvic-fin length (24.6) 17.3–25.2; caudal-fin length (22.3) 21.4–24.8; depth at anal-fin origin (16.9) 14.9–19.1; head length (34.0) 33.0–36.2; orbit diameter (11.5) 9.9–11.5; upper jaw length (19.4) 19.9–22.3 ƋƋ, 18.8–22.1. As percentage of head length: postorbital head length (63.6) 62.6–69.0; upper jaw length (57.1) 56.8–64.0 ƋƋ, 55.1– 64.2 ♀♀; postorbital jaw length (24.4) 23.4–32.5 ƋƋ, 19.5–25.7 ♀♀; orbit diameter (34.0) 27.5–33.6.

Preserved coloration. Head and body various shades of brown; several irregular, wavy rows of pale marking or oblong spots on body and a wedge-shaped basicaudal blotch extending onto middle caudal-fin rays; larger specimens with many tiny black spots scattered on head and jaws; branchiostegal membranes and 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 mostly pale except conspicuous ocellus between spines 2–5 and a narrow dark stripe immediately behind ocellus (only a continuous dark stripe in small juveniles) extending length of fin diagonally to just above base of last ray; dorsalfin spines with distinctly pale slightly fleshy tabs; anal fin pale with a narrow, suprabasal, dark stripe; pelvic, pectoral, and caudal fins immaculate.

Live coloration (based on aquarium photograph taken by P.C. Heemstra, of a 79.4 mm SL specimen from Heron Is.): pale background coloration of head and body mostly white, as are pale areas in fins; spot in ocellus black and other dark areas various shades of brown.

Etymology. The specific epithet, from the Latin semi (half) and nudus (bare, naked), refers to the naked anterior half of the body.

Distribution. Endemic to the Great Barrier Reef where collected in 0.5– 22 m.