Comprehensive DescriptionRead full entry
Figs. 1a, b
Hemigaleus microstoma : Last and Stevens, 1994: 218-219. (Plate 28, Figure 28.1); Sainsbury, Kailola and Leyland, 1985: 36, fig. Hemigaleus sp. aff. “microstoma” : Compagno, 1998: 1307. Hemigaleus sp. A : Compagno, Dando and Fowler, 2005: 285. (Plate 49).
Holotype . CSIRO H 5949-01, adult male, 919 mm TL, 41 m depth, northwest of Geraldton, Western Australia ( 28°22’ S , 113°49’ E ), 2002.
Paratypes . CSIRO H 5949-02, adult male, 1039 mm TL, same collection data as holotype ; CSIRO CA 2502, female, 478 mm TL, 120 m depth, northwest of Eighty Mile Beach, Western Australia ( 18°09’ S , 120°02’ E ), 1980 ; CSIRO CA 2503, female, 581 mm TL, 68 m depth, north of Port Walcott, Western Australia ( 19°44’ S , 117°17’ E ), 1980 ; CSIRO H 1482-04, adult female, 876 mm TL, 30 m depth, North West Shelf, Western Australia ( 20°31’ S , 116°05’ E ), 1988 ; CSIRO H 6200-01, female, 679 mm TL, 42 m depth, northwest of Dampier Archipelago, Western Australia ( 20°17’ S , 116°19’ E ), 1982 ; CSIRO CA 2504, preserved jaws only, adult female, 918 mm TL, 40 m depth, northwest of Port Hedland, Western Australia ( 19°38’ S , 118°27’ E ), 1980 ; CSIRO CA 2505, preserved jaws only, adult female, 972 mm TL, 34 m depth, east of Bedout Island, Western Australia ( 19°38’ S , 119°31’ E ), 1980 ; CSIRO CA 2506, preserved jaws only, adult male, 940 mm TL, 160 m depth, west of Roebuck Bay, Western Australia ( 18°08’ S , 119°22’ E ), 1980 ; CSIRO CA 2507, preserved jaws only, adult male, 872 mm TL, 31 m depth, north of Eighty Mile Beach, Western Australia ( 19°29’ S , 120°23’ E ), 1980 ; CSIRO CA 2508, preserved jaws only, adult male, 566 mm TL, 130 m depth, north of Bedout Island, Western Australia ( 18°29’ S , 119°20’ E ), 1980 ; CSIRO CA 2509, preserved jaws only, adult male, 891 mm TL, 40 m depth, east of Bedout Island, Western Australia ( 19°38’ S , 118°29’ E ), 1980 .
Other material not part of the type series. CSIRO H 2689-01, immature male, 599 mm TL, 50 m depth, northeast of Brunswick Heads, New South Wales ( 28°19’ S , 153°39’ E ), 1990 ; CSIRO H 2376-09, immature male, 398 mm TL, CSIRO H 2376-10, immature male, 327 mm TL, off Cairns, Queensland , 1989 ; CSIRO H 3302-01, female, 349 mm TL, 24 m depth, east of Shelburne Bay, Queensland ( 11°49’ S , 143°08’ E ), 1993 ; CSIRO H 4764-01, male embryo, 262 mm TL, 35 m depth, northwest of Port Hedland, Western Australia ( 19°43’ S , 118°22’ E ), 1989 ; QM I 14577, 2 specimens, 2 immature males, 376 and 435 mm TL, Mud Island, Moreton Bay ; QM I 27977, immature male, 366 mm TL, Gulf of Carpentaria, 18°30’S , 137°41.6’ .
Diagnosis. A medium sized hemigaleid shark with the following combination of characters: moderately long head; dorsal fins slightly raked back, moderately or not falcate, moderately low; height of first dorsal fin 2.6-3 in head length; length of first dorsal fin 2.1-2.4 times its height; caudal-fin upper lobe moderately broad, not elongate; caudalfin ventral lobe short, preventral margin 9.3-9.8% TL; pectoral fins broad, falcate, base length 2.1-2.4 in preventral caudal margin; claspers of adults moderately short, inner length 5.4-5.6% TL, 1.8-1.8 in pelvic midpoint to first dorsal-fin insertion; teeth in 28-30/ 46-52 rows; precaudal vertebral centra 65-70, total vertebral centra 112-121; second dorsal fin with a conspicuous dark tip; first dorsal fin with a pale posterior margin.
Description. Proportions as percentages of total length for the holotype and the 5 whole paratypes are presented in Table 1.
Body elongate, trunk weakly compressed, oval in cross-section at first dorsal-fin base; length of trunk from fifth gill openings to vent 1.38 (1.27-1.48) times head length; second dorsal-fin origin to anal-fin origin 3.28 (2.18-3.80) in second dorsal-fin origin to pelvicfin midpoint; anal-caudal space 6.84 (7.05-7.60) in preanal length; predorsal ridge absent; definite interdorsal ridge, extending just over half distance from first dorsal fin to second dorsal fin; postdorsal ridge absent; lateral line distinct with a pronounced dip under second dorsal-fin origin, forming a weak ridge laterally. Caudal peduncle slender, cylindrical, tapering; without lateral keels; height 1.20 (1.04-1.36) in width at upper caudal-fin origin, 3.93 (3.68-4.69) in dorsal-caudal space. Precaudal pits present and crescentic.
Head moderately long, length 0.85 (0.80-0.92) in pectoral-pelvic space; relatively narrow, moderately depressed, roughly trapezoidal in cross-section at eyes; outline of prespiracular head in lateral view nearly straight dorsally, becoming convex above gills; post-oral head slightly convex; broadly parabolic in dorsoventral view; preoral snout moderate, 1.28 (1.19-1.34) in mouth width. Snout relatively thick, bluntly rounded in lateral view, convex above and below; tip broadly rounded in dorsoventral view, with very shallow indentations anterior to nostrils.
Eyes large and oval in shape, eye length 8.40 (6.54-9.60) in head length; slightly dorsolateral on head; lower edges in line with lateral margin of head in dorsal view; subocular ridges strong; external opening with prominent posterior notch, no anterior notch; nictitating lower eyelids external; subocular pouches narrow but deep, entirely scaled with secondary lower eyelids. Spiracles minute, their length much shorter than eye to spiracle distance, located dorsally to median level of eye. First four gill slits subequal in length, much longer than fifth, height of fifth 0.68 (0.62-0.86) of first; height of first 7.01 (6.79-9.32) in head and 1.20 (0.70-1.31) of eye length. Anterior margin of gill slits undulate or slightly convex; not elevated on dorsolateral surface of head, upper margin slightly above lower edges of eyes; gill filaments not visible from outside.
Nostrils with large oval incurrent apertures lacking posterolateral keels; well in front of mouth; width 2.17 (2.16-2.32) in internarial space, 1.34 (1.21-1.72) in eye length, and 1.61 (1.20-1.81) in first gill-slit opening; excurrent apertures small, oval. Anterior nasal flaps subtriangular and moderately long, prominent mesonarial flaps, and small posterior nasal flaps. Anterior nasal aperture broadly rounded anteriorly, forming a gradual depression.
Mouth crescent-shaped and short; width 3.76 (3.45-3.74) in head length; length 2.35 (2.26-3.04) in width; tongue large, flat, broadly rounded, filling floor of mouth; buccal papillae absent; labial furrows moderately long, upper 1.69 (1.62-2.22) times lower furrows; anterior ends of uppers extending ahead of posterior corners of eyes.
Upper anterolateral teeth compressed with high crowns, broad roots, an oblique cusp, 7-10 small cusplets; primary cusps very short, only slightly larger than distal cusplets; Lower anterolateral teeth considerably smaller than upper teeth; cusps short, slender, straight, erect, with their edges sloping gradually into the edges of crown feet no cusplets; not protruding from mouth; no apparent sexual heterodonty. Tooth row groups present include medials, symphysials, anterolaterals, and posteriors in both jaws; no toothless spaces at symphysis; lower jaw with ventral edge hardly visible in lateral view; in 28-30/ 46-52 rows (from 6 paratypes based on jaws); dental formula, mean 13.2 (range 12-14) + 3.8 (3-6) + 13.5 (12-15) in upper jaw, 48.2 (46-52) in lower jaw.
Lateral trunk denticles below first dorsal fin small, closely imbricated; broad and multicuspidate with about five longitudinal ridges extending entire length of crown; crown length about equal to its width. Denticles absent near insertion of the pectoral and pelvic fins.
First dorsal fin moderately tall, not falcate; anterior margin convex, angular apically; posterior margin broadly concave; free rear tip acutely pointed; inner margin nearly straight; fin origin slightly posterior to free rear tips of pectoral fins; midpoint of base 1.10-1.20 times closer to pectoral-fin insertions than pelvic-fin origins; insertion well anterior to pelvic-fin origins; posterior margin upright or slanting slightly posteroventrally from apex; insertion almost above level of fin apex; first dorsal-fin base 1.66 (1.65-1.84) in interdorsal space, 1.44 (1.36-2.11) in dorsal caudal-fin margin; fin height 1.94 (1.56- 1.86) in base length; inner margin 2.20 (1.69-2.24) in height, 4.26 (2.64-4.17) in base length.
Second dorsal fin moderately tall, apically narrow, moderately falcate; much smaller than first dorsal fin, height 0.66 (0.61-0.0.70) of first dorsal-fin height, base length 0.65 (0.68-0.79) of first dorsal-fin base length; anterior margin weakly convex; apex narrowly rounded; posterior margin deeply concave; inner margin straight or slightly concave; free rear tip acutely pointed, terminating slightly anterior to anal-fin free rear tip and well in front of upper caudal-fin origin; origin separated from pelvic-fin insertions by a space about 1.58 (1.49-1.65) times pelvic-fin base; posterior margin extending slightly anteroventrally from apex; insertion about in level with fin apex; second dorsal-fin base length 1.24 (1.18-1.30) in dorsal-caudal space; fin height 1.89 (1.87-2.04) in base length; inner margin 1.75 (1.46-2.18) in height, 3.30 (2.83-4.36) in base length.
Anal fin low, apically narrow, semifalcate, smaller than second dorsal fin; height 0.68 (0.65-0.68) in second dorsal-fin height, base length 0.71 (0.68-0.83) times second dorsalfin base length; anterior margin weakly convex; apex narrowly rounded; posterior margin deeply notched, slanting anterodorsally from apex; free rear tip acutely pointed, well in front of lower caudal-fin origin; inner margin nearly straight; preanal ridges indistinct; origin slightly behind second dorsal-fin origin, by 0.42 (0.34-0.53) of second dorsal-fin base; insertion slightly anterior to apex, slightly behind second-dorsal fin insertion; analfin base length 1.50 (1.19-1.36) in anal-caudal space; fin height 1.96 (2.05-2.43) in base length; inner margin 1.34 (1.13-1.55) in height, 2.64 (2.61-3.17) in base length.
Pectoral fins narrow and moderately falcate; anterior margins broadly convex, length 1.49 (1.46-1.60) times posterior margin; bases narrow; apices acutely pointed, posterior margins moderately concave; free rear tips broadly rounded, inner margins strongly convex; origins under fourth gill opening; about subequal in area than first dorsal fin. Apex of pectoral fin well posterior to its free rear tip when fin is elevated and appressed to body.
Pelvic fins broadly subtriangular; area slightly greater than anal-fin area; anterior margins slightly convex, length 0.54 (0.51-0.58) length of pectoral-fin anterior margins; narrowly pointed apically; posterior margins broadly concave; free rear tips pointed, inner margins nearly straight to slightly concave. Claspers of adult male holotype relatively long and basally stout; slightly convex for most of outer margin length, tapering near tip; extending well behind pelvic-fin free rear tips, distance 1.1 times pelvic-fin inner margin; apex 1.2-1.3 times anal-fin base short of anal-fin origin; glans moderately long, length slightly more than half length of outer margin of clasper; blunt distally with a narrow apex; covered laterally and ventrally with small clasper denticles; dorsomedial surfaces of glans (including rhipidion) and lateral strip adjacent to clasper groove naked.
Caudal fin asymmetrical, upper lobe narrow; terminal lobe moderately enlarged, ventral lobe prominent, subtriangular, weakly falcate; dorsal caudal margin moderately long, 4.10 (3.39-4.35) in precaudal length, slightly convex to nearly straight, without lateral undulations; preventral margin convex, length 2.04 (1.97-2.38) in dorsal caudal margin; tip of ventral lobe acutely pointed; lower postventral margin nearly straight to concave; upper postventral margin nearly straight to slightly convex; subterminal notch a narrow, shallow slot; subterminal margin nearly straight, terminal margin slightly to strongly concave, fin tip bluntly angular; subterminal margin 1.69 (1.32-2.15) in terminal margin; caudal tip pointed, terminal lobe length 2.84 (2.83-3.09) in dorsal caudal margin.
Vertebral counts, ratios and statistics of the holotype, the 5 whole paratypes, and 4 other non-type specimens, are given in Table 2. Counts for the types are summarised as follows: total (TC) centra 113 (112-121), precaudal (PC) centra 65 (67-69), monospondylous precaudal (MP) centra 32 (32-35), diplospondylous precaudal (DP) centra 33 (34-37). Last few MP centra before MP-DP quite enlarged, not forming ‘stutter zone’ of alternating long and short centra.
Coloration. Light grey to greyish brown dorsally, whitish ventrally; tips of second dorsal fin and upper caudal fin dark, fading in larger specimens; posterior margin of first dorsal fin pale.
Size. Attains a maximum size of about 1100 mm TL; males reach sexual maturity at ~600 mm TL and females between 600 and 650 mm TL. Young are born at ~300 mm TL.
Distribution. Occurs off northern Australia from Geraldton (Western Australia) to Brunswick Heads (New South Wales). The type series was collected off northwestern Australia. Records from Papua New Guinea need to be confirmed.
Habitat. Predominantly demersal on continental and insular shelves from shallow, inshore bays down to depths of 170 m.
Etymology. Named in allusion to the known geographic range of this species (i.e. off tropical Australia).
Common names. We propose the official English common name of “Australian weasel shark”, in allusion to the known distribution of this species.
Several intraspecific, morphometric differences were observed between juveniles and subadults, and adults in both species, resulting in relatively large ranges for some characters (see Table 1). The most notable differences were in the measurements of presecond dorsal length, snout-vent length, preanal length, interdorsal distance, pectoralpelvic distance, dorsal caudal-fin margin, and head, trunk and abdomen widths. The morphometry of Hemigaleus australiensis ZBK from eastern Australia agreed with the Western Australian types. Similarly, the vertebral counts from four of the eight non-type specimens of H. australiensis ZBK agreed with those of the type series (see Table 2).
Hemigaleus australiensis ZBK is readily distinguished from H. microstoma by differences in teeth and meristics, coloration, morphometrics and size at birth and maturity (see Figs. 1a, 2). The latter species has much higher vertebral counts than H. australiensis ZBK , e.g. total vertebrae 137-164 vs 112-121, precaudal vertebrae 79-100 vs 65-70 (see Table 2).
The sizes at maturity and birth of H. australiensis ZBK are much smaller than those of H. microstoma . Stevens and Cuthbert (1983) reported a size at maturity for females and males of Australian Hemigaleus of 600-650 and 600 mm TL, respectively, and a size at birth of 260-280 mm TL. In contrast, the size at maturity for females and males of H. microstoma from eastern Indonesia is 740-800 and>790 mm TL, respectively, and the size at birth is 470-490 mm TL (W. White, unpubl. data).
Hemigaleus australiensis ZBK also differs from H. microstoma in having a dark-tipped (rather than a white-tipped second dorsal fin), a pale margin on the first dorsal fin (rather than a conspicuous white tip) and no white blotches on the sides of the body (rather than white blotches usually present).