Leptaulopus, Gomon & Struthers & Stewart, 2013

Gomon, Martin F., Struthers, Carl D. & Stewart, Andrew L., 2013, A New Genus and Two New Species of the Family Aulopidae (Aulopiformes), Commonly Referred to as Aulopus, Flagfins, Sergeant Bakers or Threadsails, in Australasian Waters, Species Diversity 18, pp. 141-161 : 151-154

Genus Leptaulopus gen. nov

Aulopus nec Cloquet, 1816 : Sulak 1977: 53; Yamakawa in Masuda et al. 1984: 60; Okamura and Amaoka 1997: 109; Paxton and Niem 1999: 1919; Nakabo in Nakabo 2000: 349; Prokofiev 2008: 141.

Hime nec Starks, 1924 : Parin and Kotlyar 1989: 407; Thompson 1998: 50; Hoese, Bray and Gates in Hoese et al. 2006: 464.

Type species. Aulopus damasi Tanaka, 1915 , by designation.

Diagnosis. Dorsal fin with 13–16 rays; pectoral fin with 12 rays; total vertebrae 36 or 44; lateral line scales 33–37 or 44. Head moderately large, length 33.1–38.7% SL; snout slightly to distinctly elongate, 10.6–12.6% SL and 30.3– 36.5% HL; eye of moderate size 6.4–10.6% SL and 19.1– 29.7% HL; bony interorbital narrow 2.4–4.0% SL; predorsal elongate 40.3–46.7% SL; anal fin to anus 9.6–14.3% SL. Nasal flap arising from septum between anterior and posterior nasal openings extremely fimbriate ( Fig. 2B, C ). Teeth in jaws very small, caniniform to cardiform, more or less of uniform size, those of upper jaw in band of about four to eight ill-defined rows, five to eight rows in lower jaw. Dorsal fin originating just behind vertical through pelvic fin origin, base moderately short 21.9–26.2% SL, moderately low without apparent sexual dimorphism in form, third ray longest, 13.6–17.6% SL, subsequent rays progressively shorter, posterior lobe of both sexes reaching little more than half way to hypural crease; no apparent sexual dimorphism in form of anal fin, with posterior lobe reaching less than half way to hypural crease; caudal fin with shallow fork, shortest rays at middle of fin about half length of longest rays to corners; ray on ventral edge of caudal fin with fleshy covering in large individuals; pectoral fin origin in advance of vertical through dorsal fin origin by distance equal to or greater than eye diameter; first four rays of pelvic fin thickened and cylindrical with fleshy dermal covering at least distally. Little if any sexual dichromatism.

Description. Dorsal fin rays 13–16; anal fin rays 8–11; caudal fin rays 10+19+8–9=37–38; pectoral fin rays 12; pelvic fin rays 9; vertebrae 20–27+15–18 = 36 or 44; lateral line scales 33–37 or 44+1; scales above lateral line 3.5; scales below lateral line 3.5 or 4.5; predorsal scales 13–20; gill rakers 2 or 3+9–12=11–15 (see Tables 2 and 4 for additional meristic and morphometric values).

Body elongate, moderately thick, of similar breadth from eyes to posterior end of dorsal fin; dorsal profile of snout straight, nape with slight convex curve, inclined to dorsal fin origin, sloping more gradually to base of tail with straight dorsal profile; ventral profile of head and body mostly straight; caudal peduncle of moderate depth; body deepest at anterior part of dorsal fin, depth at dorsal fin origin 16.8–19.9% SL; depth at origin of adipose fin 8.3–13.1% SL; anus slightly to distinctly closer to anal-fin origin than pelvic-fin origin. Head moderately large, pointed; snout slightly to distinctly elongate, slightly to much longer than eye diameter, slightly to distinctly dorsoventrally flattened, broadly to narrowly rounded from above; eye of moderate size, diameter 6.4–10.6% SL and 19.1–29.7% HL, top of eye protruding above dorsal profile of head; bony interorbital distinctly concave, narrow, interorbital width 2.4–4.0% SL and 7.0–11.1% HL; postorbital length approaching half head length. Anterior nostril small, posterior nostril much larger, anteroposteriorly elongate, about three or four times diameter of anterior nostril, both about midway between tip of snout and orbit; fimbriate tabular skin flap based on septum separating nostrils ( Fig. 2B, C ). Edge of preopercle smooth, posterior margin straight, angle about 90°, blunt; opercular margin broadly curved; without well-developed membranous lobe; branchiostegal membranes overlapping ventrally, free from isthmus. Mouth of moderate size, terminal, lower jaw not projecting in advance of upper, profile of upper jaw hidden when viewed from above; posterior end of maxilla moderately broad, posterior margin nearly straight, extending just past vertical through centre of eye, dorsal margin separated by skin covered gap from underside of eye with mouth closed; upper lip broad, covering upper jaw laterally with mouth closed. Teeth in jaws very small, caniniform to cardiform, those of upper jaw in band of about four or five poorly-defined rows laterally and four to seven ill-defined rows anteriorly, more or less of uniform size, smaller teeth on side of jaw near front, distinct hiatus of teeth at symphasis; band of five to eight ill-defined rows of teeth laterally in lower jaw, band narrower in about four or five rows at front, inner row of noticeably larger teeth mesially in some; triangular naked hiatus in dentition at symphasis. Band of two or five rows of small canines on palatines, mesial row longest, and bilateral pair of dentate patches of teeth on vomer, interconnected by row of smaller teeth medially in large individuals. Gill rakers moderately long and slender.

Scales of moderate size, finely spiniform along margins, not extending onto fins, except caudal fin with small scales dorsally and ventrally at base; scales on breast and anteriorly on belly cycloid to weakly spiniform. Predorsal scales extending forward to vertical through posterior extent of eye, covering opercle and preopercle forward to posterior end of maxilla; axial scale present at origin of pectoral and pelvic fins. Lateral line midlaterally on side, originating at horizontal through upper margin of eye; lateral line scales corresponding with oblique scale rows above and below lateral line; single pore on each lateral line scale.

Dorsal fin originating just behind vertical through pelvic fin origin, distance from snout tip to dorsal fin origin 40.3– 46.7% SL; dorsal fin base moderately short, length 1.12–1.38 times distance from dorsal fin insertion to origin of adipose fin; fin moderately low without apparent sexual dimorphism in form; third ray longest, rays progressively decreasing in length posteriorly; posterior lobe reaching little more than half way to hypural crease; distance from dorsal-fin origin to tip of posterior lobe 30.7–36.2% SL; first two dorsal-fin rays unbranched, others branched. Adipose fin rather small but prominent, positioned above posterior end of anal-fin base. Anal fin originating slightly behind or slightly in advance of vertical through midpoint between dorsal fin insertion and adipose fin, with short base, length 8.2–10.2% SL; of moderate depth, rays progressively decreasing in length posteriorly without apparent sexual dimorphism in form; posterior lobe reaching much less than half way to hypural crease; first two or three rays unbranched, others branched. Caudal fin with shallow fork, shortest rays at middle of fin about half length of longest rays extending to corners, lobes bluntly pointed, lobes of similar length; rays near ventral margin of fin more densely segmented than those near dorsal margin of fin; unbranched ray at ventral margin with opaque fleshy covering ventrally in large individuals. Pectoral fin of moderate size, tip reaching vertical through middle of dorsal fin base; origin of fin well in advance of vertical through dorsal fin origin by distance equal to or greater than eye diameter; first two rays simple, others branched, third longest, subsequent rays progressively shorter. Pelvic fins moderately large, posterior tip of depressed fin reaching just past anus; first four rays distinctly thickened and cylindrical with fleshy dermal covering at least distally, densely segmented, first ray unbranched, second to fourth each with a pair of simple thickened branches, subsequent rays progressively shorter, flattened with typical multi-branching, except for inner-most unbranched ray.

Species attain moderate size.

Etymology. The generic name Leptaulopus is a combination of the Greek leptos for ‘slender’ and aulopus, a name long applied to the broader group of fishes to which the genus belongs, in reference to the slender form of species it comprises.

Discussion. Shimizu and Yamakawa (1989) distinguished this genus from Aulopus , Hime and Latropiscis on the basis of the length of the snout relative to the eye diameter, length of the dorsal fin base relative to the distance from the dorsal fin insertion to the adipose fin origin and position of the dorsal fin origin relative to the pelvic fin origin. They also noted distinct differences in meristic values between the two species they referred to it, Aulopus damasi and the new species described below. While species of the genus Hime are extremely conservative meristically, the two species of Leptaulopus differ greatly in the numbers of dorsal fin rays, lateral line scales, and vertebrae, despite their overall similarity in appearance. These differences, as well as several others evident in relative morphometric dimensions discussed in species treatments, are consistent with genetic distances observed above but are not regarded as more than intrageneric variation. Species of Aulopus also exhibit considerable variation in values for meristic characters, as reported by Thompson (1998) for the eastern Pacific A. bajacali with 14–17 dorsal fin rays, 48–54 lateral line scales and 47–53 vertebrae.

Species of Leptaulopus have a slender body when compared with species of Hime and Latropiscis (16.8–19.9 vs 16.6–24.3 and 18.7–21.4 respectively, based in part on values reported by Parin and Kotlyar 1989 and Matsunuma et al. 2008) and narrower interorbital (2.4–4.0 vs 3.2–6.1% SL and 7.0–11.1 vs 10.3–19.5% HL, respectively). They have typically 12 pectoral fin rays, while species of Hime and Latropiscis have typically 11 and Aulopus mostly 13. As in species of Aulopus , the origin of the dorsal fin in Lepataulopus is posterior to a vertical through the pelvic fin origin rather in advance of it, but the predorsal distance is markedly greater than species in any of the other three genera (40.3–46.7 vs 32.6–40.1% SL). Species of Leptaulopus , like those of Hime and Latropiscis , have the anus positioned well in front of the anal fin origin, considerably more so than described above for Aulopus . Teeth on the jaws of Leptaulopus are finer, more cardiform than caniniform and far more numerous than in species of the other genera. Leptaulopus species also have extremely fimbriate nasal flaps arising from the septum between the anterior and posterior nasal openings, in contrast to the lanceolate flaps of Hime spp. ( Fig. 2A–C ), as well as Aulopus spp , and the rectangular flaps with uneven to lobate distal margin in Latropiscis . Species of Aulopus and Leptaulopus appear to lack the expansion of the dorsal fin characteristic of males of Hime and Latropiscis , even if males in Aulopus may have prolonged anterior fin rays.

Figures

Fig. 2. Nasal flap: A) Hime pyrhistion sp. nov. NMNZ P.054047, holotype; B) Leptaulopus damasi NSMT-P. 115220, neotype; and, C) Leptaulopus erythrozonatus sp. nov. NMNZ P.042518, holotype.