Sinobatis brevicauda Weigmann & Stehmann, 2016, n. sp.
Creators: name: Weigmann, Simon
name: Stehmann, Matthias F. W.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Rajiformes
Anacanthobatidae
Sinobatis
Sinobatis brevicauda

description: Sinobatis brevicauda n. sp.
(Shorttail Legskate)
Figures 2–19; Table 1
Anacanthobatid sp.— Weigmann et al., 2014: 128.
Sinobatis cf. bulbicauda — Weigmann, 2016: 962.
Holotype ZMH 26158, presumably adult female, 591 mm TL and 422 mm DW fresh (fresh TL measured including rostral filament), 574 mm TL and 418 mm DW 70% ethanol preserved, RV ‘Vityaz’, cruise 17, station 2820, Saya de Malha Bank, 08°34’S, 59°40.1’E – 08°24.7’S, 59°43.5’E, 960–1130 m depth, 28 m shrimp trawl, trawl # 97, on the bottom for 80 minutes, 10 Jan 1989.
Paratype ZMH 26159, presumably adult female, 568 mm TL and 388 mm DW fresh (fresh TL measured including rostral filament), 546 mm TL and 385 mm DW 70% ethanol preserved, data the same as holotype.
Diagnosis. A large western Indian Ocean anacanthobatid species growing to about 591 mm TL, with an extremely depressed pear-shaped, broad and long disc (width 71–73% TL, length 76% TL), 0.9–1.0 times as wide as long and with rounded outer corners. Head (dorsal length 34% TL, ventral length 41% TL) and snout (preorbital length 28–29% TL, preoral length 30% TL, prenasal length 28% TL) long; snout angle 90–93°; snout terminally expanded as a rostral lobe that is 12–13% of preorbital snout length and with a short, thin rostral filament. Interorbital distance rather wide, 4% TL. Inner margin of posterior pelvic lobe fused to root of tail along most of its length with a short, pointed free tip. Tail very short, length from mid-vent to tail tip 35–36% TL and about half of body length from tip of rostral lobe to mid-vent; tail tapering from anterior part towards about mid-length of tail, but becoming slightly broader and flattened in posterior third through lateral keels, and tapering again towards tip from about 2 cm before tip. Caudal fin rudimentary with very short and low epichordal and without hypochordal lobe. Upper and lower surfaces of disc and tail entirely naked and without papillae. Upper surface pale grayishbrown, ventral side anteriorly whitish to level of lower jaw and interbranchially, posterior part of disc and underside of tail pale grayish-brown with irregular pale brown blotches at transition from white to brown, underside of posterior pelvic lobe medium grayish-brown, anterior lobes dark brown with an indistinct white blotch near the tip and a distinct white blotch at anterior origin. Upper jaw tooth rows 25–27, monospondylous vertebral centra 29, diplospondylous centra 102–112, total centra 131–141. Scapulocoracoid subrectangular, with rear corner sharply marked; moderately large oval anterior fenestra without anterior bridge, one very large oval postdorsal and at least three small postventral fenestrae. Pelvic girdle with massive ischiopubic bar with almost straight anterior and broad, shallow trapezoid posterior contour; prepelvic processes very long and slightly inclined outwards, their length from axis of pelvic girdle maximum width 77.5–90.9% of pelvic girdle maximum width and 4.9–5.6 times median thickness of ischiopubic bar. The new species differs from all other described anacanthobatids in the short tail, which also discriminates it from its morphologically closest congener, the allopatric Sinobatis bulbicauda. Sinobatis brevicauda n. sp. is further distinguished from the other anacanthobatid legskates in the western Indian Ocean, Anacanthobatis marmorata and Indobatis ori, by its large size and light coloration.
Description of the holotype (Figs. 2–19). Values of the paratype with extreme tail tip missing but healed in parentheses if differing. Where relevant, ratios are based on horizontal measurements unless otherwise stated. Detailed morphometric measurements and meristics are given in Table 1.
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External morphology (Figs. 2–14): Disc extremely depressed pear-shaped, consistency of body flabby; anterior margins slightly convex, outer and inner pectoral corners broadly rounded, posterior margins evenly convex, pectoral axils fused to outer margin of posterior pelvic lobes except for short triangular indention separating both; disc broad and long (width 71–73% TL, length 76% TL), disc width 1.0 (0.9) times disc length, disc length 2.7 (2.6) times the preorbital snout length and 2.5 times the preoral snout length; axis of maximum disc width at 41% (42%) TL (Figs. 2–7). Head long, dorsal length 34% TL. Snout long and pointed, gradually tapering to the rostral lobe slightly marked off; rostral filament present; snout pointed at about 90° (93°); preorbital snout length 28% (29%) TL, 6.7 (6.6) times interorbital width, and 2.6 (2.5) times in disc width (Fig. 8). Eyes and orbits small and not elevated above level of cranium, orbits not well-defined, their estimated horizontal diameter 0.8 times interorbital width and 12% (13%) of preorbital snout length; interorbital width rather large, 4.2% (4.3%) TL; spiracles small and circular, close posterior to eyes, their length 30% (23%) of orbit horizontal diameter; interspiracular space 1.9 times interorbital width; pseudobranchial folds not detectable (Fig. 9). Tail very short and depressed cord-like; anteriorly more or less oval in cross section; slightly tapering from anterior part towards about mid-length of tail, becoming slightly broader and flattened in posterior third through lateral keels and tapering again towards tip from about 2 cm before tip; length from mid-vent to tip 0.55 times body length from tip of rostral lobe to mid-vent; tail length only 35–36% TL; no dorsal fins; no lateral tail folds; relation tail width to height at level of pelvic tips 1.7 (1.4); caudal fin rudimentary, epichordal caudal lobe very short and low (missing), hypochordal lobe absent (Figs. 10–12).
Ventral head length 41% TL and 6.1 (6.0) times internarial width; preoral snout length 30% TL and 4.3 (4.2) times mouth width; prenasal length 27.9% (27.8%) TL (Fig. 13). Mouth cavity with papillose integument, mouth moderately large, jaws straight; mouth width 7.1% TL, 17% of ventral head length, and 1.1 (1.0) times the internarial space; 27 (25) tooth rows in upper and 26 (25) in lower jaws, set in quincunx pavement pattern; individual tooth with low, broadly ovoid base, flat crown, and with very short and stout, conical cusp at inner edge (Fig. 14). Gill openings small, length of first gill slit 1.0% (1.1%) TL; distance between fifth gill slits 69% (70%) of distance between first gill slits, the latter 2.3 times the internarial space. Anterior nasal flaps low and fleshy, edges weakly serrated and undulated, terminal part with short fringes; nasal curtain oriented in longitudinal direction and laterally protruding, with papillae on underside, outer edges broadly angled at about 90° and finely fringed, apices angular, nearly transversal posterior margins set with short and stout, fleshy fringes; isthmus deeply arc-shaped; oronasal pits absent. Pelvic fin anterior lobes slender and leg-like, evenly tapering to tip and with diagonal, jagged terminal edges with pointed tips, anterior lobes separated from posterior ones and 0.9 times as long as posterior lobes; posterior lobes fin-like, their inner margins fused to root of tail along most of their length with a short, pointed free tip (Figs. 10–11).
Dorsal and ventral surfaces completely without papillae. Distinct pores only present on anterior half of ventral disc from snout tip to slightly posterior to level of mouth (Fig. 13). No transversal row of pores internasally (Fig. 14).
Squamation (Figs. 2–7): Upper and lower surfaces of disc and tail entirely naked.
Coloration (when fresh, Figs. 2–3): Dorsal side plain medium grayish-brown, slightly darker than ventrally. Anterior disc margins including snout tip and filament, as well as pectoral apices white; rostral triangle except for rostral cartilage almost translucent. Eye balls blackish-blue, eyes largely concealed by grayish-brown skin; white blotch medially on interorbital space and tail with white tip (no white blotch interorbitally and no white-tipped tail in paratype); interspiracular pores indistinct. Ventral side white anteriorly to level of lower jaw except for brown blotch on left posterior snout side and brown specks to level of nostrils (brown blotch and specks absent in paratype), white stripe over propterygia alongside gill slits, white also interbranchially medially and over shoulder girdle, narrowing triangularly onto anterior belly. Patch of light brown specks besides mouth-nasal region, around gills and more distinct blotching on posterior interbranchial space. Posterior half of disc, pelvics and tail medium grayish-brown except for white blotch at half length of tail and end of tail speckled with white (anterior third of tail medium grayish-brown but rest of tail white in paratype). Axils of anterior pelvic lobes with large white blotch and anterior edge of distal lobe with white markings. Distal third of anterior pelvic lobe with pale blotches in holotype but absent in paratype. Small white spot on origin of tail at fusion of posterior pelvic lobe.
Color in preservative (Figs. 4–7): Generally more uniform than in fresh condition as whitish areas have become beige and brown areas have faded to lighter brown.
Snout skeleton and cranium (Fig. 15): Anteriormost pectoral skeleton elements falling short of rostral tip. Rostral cartilage to rostral tip very slender and flexible though well calcified; its length about three times length of neurocranium. Single cranial fontanelle very elongated but distal tip and posterior contour not clearly visible, gradually narrowing to bluntly rounded tip; length of cranial fontanelle approximately 42% (41%) of total cranial length and reaching forward about 49% (41%) into rostrum length. Maximum cranial width across nasal capsules about 35% of total cranial length; maximum occipital width of neurocranium about 60% of maximum cranial width; minimum dorsal interorbital width about 35% of maximum cranial width.
Pelvic girdle (Fig. 16): Rather narrow typical anacanthobatid element with massive iliac regions, with only one large foramen posteriorly; anterior edge of ischiopubic bar almost straight, posterior contour a broad, shallow trapezoid; prepelvic processes solid, only moderately tapering to blunt tip, very long and slightly curved outward; their length from axis of maximum pelvic girdle width 77.5% (90.9%) of maximum pelvic girdle width, 60.4% (71.4%) measured from level of anterior contour of pelvic girdle medially. Maximum width of pelvic girdle 47.1% (43.0%) of maximum width of shoulder girdle.
Scapulocoracoid (Fig. 17): The element was not dissected of the only two available type specimens, but radiographs taken in oblique view of the well calcified type specimens offered a good imagination of the scapulocoracoid's shape and morphology details. Overall shape elongated rectangular and strongly asymmetrical regarding position of the mesocondyle; post-mesocondyle length about three times pre-mesocondyle length. Moderately large anterior fenestra subcircular and not divided by anterior bridge; its position almost completely above longitudinal axis of scapulocoracoid. Single very large postdorsal fenestra of horizontally ovoid shape and about three times as long as anterior fenestra. At least three postventral foramina much smaller and in horizontal line below radial bearing post-mesocondyle ridge. Dorsal edge of the element weakly concave and gently sloping to well marked rear corner; posterior margin sloping concavely to metacondyle. Scapular process short and subquadrangular, with slightly oblique edge.
Shoulder girdle (Figs. 18, 19): Radial bearing first propterygial basal element of pectoral fin skeleton inserting at mesocondyle much shorter than further anterior basal elements, about 8 times in length of the next anterior element, which is an undivided, long cartilage as typical for female anacanthobatids (see Weigmann et al., 2014). First metapterygial basal element very long, about as long as maximum length of scapulocoracoid, and bearing by far the majority of posterior pectoral radials; the very much shorter second and final metapterygium bearing only two radials laterally and two splitting from its posterior tip, respectively.
Skeletal meristics (from radiographs, Table 1, Fig. 18): Trunk vertebrae (Vtr): 29; tail vertebrae: 112 (102); total vertebrae: 141 (131); pectoral radials left/right: 72/72 (71/71); pelvic radials left/right: 3+16/3+16. Tail vertebral and total vertebral counts of the paratype probably lower due to missing tail tip.
Size. A large legskate species reaching at least 591 mm TL.
Distribution (Fig. 1). The new species is known only from the Saya de Malha Bank in the western Indian Ocean where the type specimens were caught in 960–1130 m depth. The new species represents the first Sinobatis species recorded from the western Indian Ocean.
Etymology. The species name (lat. brevis = short, lat. cauda = tail) refers to the very short tail of the new species.
Remarks. Sinobatis brevicauda n. sp. is placed in the genus Sinobatis in spite of the absence of adult males due to its apparent similarity and relationship to S. bulbicauda. A detailed comparison of these two species can be found in the Discussion.
description: Published as part of Weigmann, Simon & Stehmann, Matthias F. W., 2016, Sinobatis brevicauda n. sp., a new deep-water legskate (Rajiformes, Anacanthobatidae) and first generic record from the western Indian Ocean, pp. 478-500 in Zootaxa 4137 (4) on pages 480-492, DOI: 10.11646/zootaxa.4137.4.2, http://zenodo.org/record/268229