Sinobatis caerulea, Last, Peter R. & Séret, Bernard, 2008

Last, Peter R. & Séret, Bernard, 2008, Three new legskates of the genus Sinobatis (Rajoidei: Anacanthobatidae) from the Indo – West Pacific, Zootaxa 1671, pp. 33-58 : 43-47

Sinobatis caerulea new species

Figs 6–8 , 11 , 13 ; Table 2

Anacanthobatis sp. C: Last & Compagno, 1999, Anacanthobatidae , leg skates. In: Carpenter & Niem (eds), 1999, FAO species identification guide for fisheries purposes. The marine living resources of the Western Central Pacific, pp 1464, listed.

Holotype. CSIRO H 2550–10, immature male, 539 mm TL (332 mm DW), 1100–1158 m depth, W of North West Cape, Western Australia (21°54'S, 113°40'E), 1991.

A B Paratypes. 4 specimens: CSIRO H 2550–01, female, 684 mm TL (428 mm DW), same data as holotype; CSIRO H 2569–02, male, 407 mm TL (230 mm DW), 1115–1125 m depth, W of Dirk Hartog Island, Western Australia (25°41'S, 111°30'E), 1991; MNHN 2007–1473, female, 332 mm TL (198 mm DW) and WAM P 32864–001, female, 356 mm TL (201 mm DW), 482–544 m depth, SW of Point Cloates, Western Australia (22°59'S, 113°14'E), 1991.

Diagnosis. A species of Sinobatis with the following combination of characters: large disc (width at anterior orbit 8.0–9.1 times mouth width); short tail (postcloacal length 35–42% of disc length); relatively small eyes, orbit diameter 10.9–15.7 in horizontal snout and 13.1–17.9 in head lengths respectively; distal portion of tail weakly or slightly expanded, width of tail near tip 1.5–1.6 times tail width at its midlength; pectoral-fin radials 72–76; moderate-sized pelvic fins, anterior lobe 15.4–16.0% TL; anterior pelvic-fin lobe rather broadbased, width 1.7–2.2 in distance between pelvic-fin origins; caudal fin rudimentary; 24–30 tooth rows in each jaw of adults; monospondylous vertebral centra 26–29, total centra 184–212; dorsal and ventral surfaces bluish in fresh specimens.

Description. Medium-sized anacanthobatid with extremely depressed pear-shaped disc (extremely variable between growth stages and between sexes), its width 1.09 in holotype (1.16 in male paratype, 1.12 in largest female paratype) in length from base of rostral filament; axis of maximum width at 58% (57%, 62%) of disc length, outer and inner corners broadly rounded. Tail short, very slender, slightly depressed anteriorly; midlength almost square in cross-section; laterally expanded slightly posteriorly, not spatulate (much less expanded in paratypes); tapering just before caudal fin, filamentous near tip; length much shorter than trunk length, cloaca to tip of tail 1.55 (1.38, 1.90) in snout-cloaca length (from base of rostral filament), 1.57 (1.35, 1.81) in disc width, 1.71 (1.57, 2.03) in disc length; with weak lateral cutaneous folds. Head relatively long, dorsal length 32.6% (32.6%, 34.9%) TL, ventral length 38.3% (38.0%, 41.8%) TL. Snout relatively long, its preorbital length 6.74 (6.53, 5.73) times longer than interorbit, 26.7% (28.1%, 30.7%) TL; angle forward of spiracles acute, 80° (78–79°); snout tip with a broad, elongate, narrowly triangular rostral lobe; short filament at apex of rostral lobe. Orbits very small, horizontal diameter 10.9 (11.3, 15.7) in preorbital snout length, 1.62 (1.72, 2.75) in interorbit. Spiracles small, about half length of orbits, subcircular; combined orbit and spiracle length 3.7% (3.5%, 3.2%) TL. Mouth weakly convex in holotype (straight to weakly convex in paratypes), upper jaw slightly concave at symphysis (less so in paratypes); width 5.52 (5.54, 6.52) in preoral length, 7.46 (7.20, 8.43) in ventral head lengths; teeth with an irregular oval base, rhomboidal crown with rudimentary posterior cusp, cusp often barely detectable; no information for adult males. Anterior nasal lobes very small, strongly fringed, confined to anterior lateral margins of nostril; oronasal grooves well developed. Posterior nasal lobes enlarged, weakly connected basally by low, fleshy, concave skin folds; not united medially, not forming a well-defined nasal curtain; lobe with prominent, simple or complex, dermal fringe along posterior margin; almost overlapping corners of mouth. Rostral cartilage prominent, flexible, moderately well undulated (more so distally). Upper and lower surfaces of disc and tail entirely naked in females. Mucous pores on dorsal surface distinct (dark edged), well developed around orbit, on mid-line and around margin of disc; 3–4 (2–4) pores lateral to eye and spiracle; 2 (0–2) pores medial to spiracle, and a single postcranial pore on each side of midline; a few minute tubelike papillae on dorsal surface, barely detectable without magnification; skin thin on dorsal surface, somewhat deciduous, less deciduous ventrally. Anterior margin of disc weakly double concave, strongly concave at base of rostral lobe; interspiracular distance 6.56 (7.66, 6.91) in width at anterior margin of orbit, 5.24 (5.64, 5.33) in dorsal head length, 2.55 (2.32, 3.36) times orbit diameter; posterior half of disc appearing semicircular, posterior pectoral-fin margins almost uniformly rounded, pectoral axils fused to anterior lateral margin of posterior pelvic-fin. Anterior lobes of pelvic fins relatively broad, depressed, freely articulating at base, leg-like, well separated from posterior lobes; posterior lobes narrowly suboval posteriorly, length 1.18 (1.21, 1.17) of anterior lobe length, their posterior margins fused to ventrolateral margin of tail just forward of their distal tip; anterior portion of posterior lobe fused to disc. Clasper of adult male unknown. Caudal fin low, elongate, epichordal lobe longer (only slightly shorter than mouth width), taller than hypochordal lobe. No dorsal fins. Tooth rows in upper jaw 25 (24–29); in lower jaw 25 (27– 30). Vertebrae: monospondylous centra 29 (26–29), diplospondylous centra 183 (155–173), total centra 212 (184–199). Pectoral fin: propterygial radials: 24–25 (23–26), mesopterygial radials 20–21 (19–21), metapterygial radials 30 (30–31), total radials 75 (72–76). Pelvic fin: in males 4 (4) + 12–13 (12–13) radials; females 4 + 14–15 radials.

Colour. Fresh coloration. Upper surface of disc bluish (deeper blue in smaller paratypes); posterior margin darker than anterior margin; rostral lobe often contrasted with rest of disc, white with blackish distal filament (more uniformly blue in paratypes); tail probably similar to disc when undamaged, mostly white in types where skin has been abraded; white scars all over disc and white patches where skin has been abraded; ocular membrane and spiracle bluish black, eyeball barely visible beneath skin dorsally; sensory pores, including those on mid and posterior disc, dark edged. Ventral surface bluish, similar to dorsal surface (slightly darker than dorsal surface in paratypes); strongly demarcated white area around mouth in all types; cloaca whitish; holotype with whitish rostral lobe and posterior margin of posterior pelvic-fin lobe (more uniformly dark in paratypes); immature male paratype (CSIRO H 2550–10) with black lateral margin on clasper. Preserved specimens faded, bluish areas become greyish; white areas remaining prominent.

Size. To at least 69 cm TL (disc width 43 cm); largest immature male 54 cm TL (disc width 33 cm); smallest neonatal juvenile 33 cm TL (disc width 20 cm).

Distribution. Upper to mid continental slope of Western Australia from west of Dirk Hartog Island (25°41'S, 111°30'E) northwards to west of North West Cape (21°51'S, 113°41'E), in depths of 482–1168 m.

Etymology. Derived from the Latin caeruleus with reference to its blue dorsal and ventral coloration. Known in the vernacular as Blue Legskate.

Remarks. This species is provisionally placed in the genus Sinobatis in the absence of adult males being available for examination. Sinobatis caerulea co-occurs with a smaller legskate, S. bulbicauda , off Western Australia. It differs from S. bulbicauda (in specimens exceeding 400 mm TL) in coloration (dark blue on all surfaces vs. pale greyish pink dorsally and white ventrally), in having a longer disc (length 65.9–69.9% vs. 59.7–65.3% TL) with a broader width at the orbit (width across anterior margin of orbit 40.8–44.3% vs. 30.3– 32.4% TL in males, 45.3% vs. 41.0–42.2% TL in females), longer snout (horizontal preorbit 26.7–30.7% vs. 19.2–25.2% TL, preoral length 28.3–32.3% vs. 21.4–27.4% TL), larger head (dorsal length 32.6–34.9% vs. 25.6–30.8% TL, ventral length 38.0–41.8% vs. 33.3–36.1% TL), smaller orbit (horizontal diameter 2.0–2.5% vs. 2.9–3.3% TL), narrower interspiracular width (5.8–6.6% vs. 6.5–7.6% TL), narrower internarial width (4.7–4.9% vs. 5.2–6.1% TL) and nasal curtain (width 5.5–6.0% vs. 6.8–7.4% TL), and lacks a well-developed, flattened filament near the tail tip. Sinobatis caerulea is the largest of the western Pacific legskates. The largest female (684 mm TL, 428 mm DW) is bigger than the large female of Sinobatis borneensis (probably = S. melanosoma ) figured by Ishihara (1984) and discussed above (594 mm TL, 377 mm DW). Sinobatis melanosoma differs from S. caerulea in having a dark brownish disc (rather than bluish), noticeably darker orbito-spiracular region, more slender anterior pelvic-fin lobe, more obtuse snout, and a much shorter direct preorbital snout length (20.9% vs. 28.1% TL in similar-sized immature males, respectively CSIRO H 4125– 0 1, 382 mm TL and CSIRO H 2569–02, 407 mm TL).

TABLE 2 Morphometric data for the mature male holotype of Sinobatis caerulea sp. nov. (CSIRO H 2550–10), with ranges for single male (CSIRO H 2569–02) and female (CSIRO H 2550–01) paratypes. Total lengths (TL) are expressed in mm, other measurements as percentages of TL.

Figures

FIGURE 6. Sinobatis caerulea sp. nov., holotype, CSIRO H 2550 – 10, 539 mm TL, immature male: A, dorsal surface; B, ventral surface.

FIGURE 7. Sinobatis caerulea sp. nov., paratype, CSIRO H 2550 – 01, 684 mm TL, female: dorsal surface.

FIGURE 8. Oronasal region and tooth bands of Sinobatis caerulea sp. nov.: A, holotype, CSIRO H 2550 – 10, 539 mm TL, immature male; B, paratype, CSIRO H 2550 – 01, 684 mm TL, female.

FIGURE 11. Dorsal view of posterior tail of: A, Sinobatis bulbicauda sp. nov., holotype, CSIRO H 2557 – 01, 429 mm TL, adult male; B, S. caerulea sp. nov., holotype, CSIRO H 2550 – 10, 539 mm TL, immature male; C, S. filicauda sp. nov., holotype, CSIRO H 948 – 02, 548 mm TL, adult male.

FIGURE 13. Distributional ranges of Australian Sinobatis species: S. bulbicauda sp. nov. (light grey), S. caerulea sp. nov. (dark grey), S. filicauda sp. nov. (black). The type locations are given for each species: S. bulbicauda (black circle), S. caerulea (black star) and S. filicauda (white star).