Aptychotrema timorensis, Last, 2004

Last, Peter R., 2004, Rhinobatos sainsburyi n. sp. and Aptychotrema timorensis n. sp. - Two New Shovelnose Rays (Batoidea: Rhinobatidae) from the Eastern Indian Ocean, Records of the Australian Museum 56 (2), pp. 201-208 : 203-204

Aptychotrema timorensis n.sp.

Figs. 1 , 2 , Plate 1 a, Table 1

Aptychotrema sp. —Gloerfelt-Tarp & Kailola, 1984: 31, fig. (of CSIRO CA1258).

Aptychotrema sp. 2 .— Sainsbury et al., 1985: 44–45, fig. (of CSIRO CA1258).

Aptychotrema sp. A .—Last & Stevens, 1994: 284, 285, pl. 40, figs. (of CSIRO CA1258).

Type material. HOLOTYPE: CSIRO CA1258 , female, 582 mm TL, 10°14'S 130°03'E, north of Bathurst Island , Northern Territory, 124 m, 8 Jul. 1980.

Diagnosis.An Aptychotrema distinguished by the following combination of characters: disc relatively large, broadly wedge-shaped, with a narrowly pointed snout; orbit diameter equal to interorbital width; tail short, about 1.1 times precloacal length; mouth small, precloacal length about 8 times mouth width; first dorsal-fin short, length 6% TL, about 2.3 times in interdorsal distance; dorsal-fin apices angular; caudal fin short, dorsal margin 12% TL; pelvic fin large, length about 2.8 times width; post-synarcual vertebral centra 156; nasal lamellae 27; ventral tip of snout not blacktipped; and dorsal surface covered with small, white spots.

Description. Disc broadly wedge shaped, angular anteriorly, angle anterior to eyes about 55°; outer margins broadly rounded, narrowly rounded distally, length 1.31 times width. Pelvic fins elongate, long-based, base length 1.46 times inner margin; total length 1.58 times their base length, 2.78 times width; anterior margin weakly convex, apex broadly rounded, posterior margin almost straight. Tail depressed, broad anteriorly, tapering; in cross-section nearly flat below, rounded above; tail length from anterior cloaca 1.14 times precloacal length, 1.11 times disc length, 5.51 times width at pelvic-fin insertions; tail width 2.20 times depth at pelvicfin insertions, 1.89 at first dorsal-fin origin, 1.72 at second dorsal-fin origin. Dermal fold lateral on tail, originating about eye diameter behind free rear tip of pelvic fin, reaching just behind ventral caudal-fin origin; fold moderate, its width uniform along interdorsal space.

Head long, ventral length 29.7% TL; snout moderately long and bluntly pointed; preoral snout length 3.42 times mouth width, 6.93 times internarial distance, 1.65 times dorsal caudal-fin margin, 5.18 times distance from nostril to margin of disc; preorbital snout length (direct) 3.19 times interspiracular length, 5.21 times orbital diameter, 5.26 times interorbital width; interorbital space slightly concave, width moderate; eyes moderately small, not elevated or protruding, orbital diameter 1.51 times spiracle length, 1.01 times interorbital width. Spiracle subrectangular, size moderate; no folds on posterior margin. Nostril small, transverse, nasal flaps moderately developed; anterior aperture oval, width exceeding length; nostril length 2.39 times anterior aperture width, 1.53 times anterior nasal-flap base length, 0.65 times in distance from nostril to edge of disc, 0.87 times internarial distance. Anterior nasal flap narrow with long, slender process anteriorly, tapering with crenulate margin posteriorly; flap base 1.45 times its width at process, 1.56 times anterior aperture width; inserted near innermost margin of nostril; distance between insertions of flaps 2.87 in greatest distance across nostrils, 1.10 in minimum internarial distance; process of flap about twice as long as wide, bluntly pointed distally, weakly overlapping posterolateral nasal flap and determining posteromesial margin of anterior aperture. Posterolateral nasal flap lobelike, broadest anteriorly, length 3.73 times width; originating at lateral extremity of anterior nasal aperture, extending posteromesially as a free fold almost to innermost edge of nostril. Posterior nasal flap weakly lobe-like laterally, base length 4.52 times its width, reaching innermost margin of nostril as thin fold; width 0.46 of anterior aperture width, 0.83 of posterolateral nasal-flap width. Nasal lamellae 27. Mouth narrow, width 2.34 times nostril length, 8.03 in precloacal length; positioned over hind margin of orbit; jaws strong, thick. Upper jaw strongly convex, arched; deep preoral groove demarcating upper lip, strongly arched, following profile of upper jaw; lower lip pronounced, postoral groove well developed, no ridges of strongly corrugated skin on chin; weak, short lateral grooves around corners of mouth. Teeth small, blunt, crowns rhomboidal with weak, pointed posterior cusps; teeth quincuncial, about 76 rows in upper jaw; upper and lower jaw teeth similar in shape and size. Gill openings s-shaped, fifth less so; length of third gill slit 1.60 in nostril length, 6.07 in distance between fifth gill slits; distance between first gill slits 1.43 times distance between fifth gill slits; distance between fifth gill slits 3.28 times internarial distance, 1.62 times mouth width, 0.32 of ventral head length.

Dorsal-fins moderately upright, apices angular; anterior margins weakly convex, posterior margins almost straight; free rear tips forming right angle, not produced; first dorsalfin slightly taller than second, length of first 0.94 times its height, base length 1.87 times inner margin length; second dorsal-fin length 1.10 times its height, base length 2.26 times inner margin length. First dorsal-fin well behind pelvic-fin insertion, interspace 1.28 times interdorsal distance; interdorsal space relatively short, 1.56 times second dorsalfin height, 2.29 times base of first dorsal-fin, 1.59 times interspace between second dorsal-fin insertion and upper origin of caudal fin; 1.45 times tail width at first dorsal-fin origin. Caudal fin relatively small, short, dorsal caudal margin 2.02 times preventral margin length.

Dermal denticles small, close-set, covering entire body and fins; surfaces uniform, coarsely granular but becoming enlarged slightly in some regions; slightly enlarged middorsally on disc and tail. Thorns present around preorbit, postorbit, spiracle, scapular region and along dorsal midline; mostly of similar size, crowns very short, globular, tips mostly blunt; bases embedded; single row of irregularly, mostly widely, spaced thorns extending from just behind head to near origin of first dorsal-fin; evident as enlarged denticles on interdorsal midline; median thorns uniform in size, about 29 in single series; two widely separated scapular thorns on each side, their sizes variable but similar to those of dorsal midline; pair of slightly enlarged globular denticles near snout tip.

Prebranchial sensory pore patch indistinct, extending posteriorly to first gill slit. Postscapular sensory canals deeply embedded, not undulated anteriorly, almost reaching pectoral-fin insertions; sensory pores not evident; sensory canal not forming a shallow groove.

Rostral cartilage moderately robust, weakly constricted near midlength, length about 64% of length of neurocranium; rostral appendix expanded, narrowly rounded apically, posterior margin short, strongly concave. Precerebral anterior fontanelle broad, acorn-shaped, extending forward from just posterior to rostral base to rostral appendix; dorsal edges of fontanelle well defined, narrowly separated near base, becoming considerably more constricted anteriorly; ventral edges not detectable; cranial roof lacking posterior fontanelle. Nasal capsules small, ovoid, length shorter than width, their transverse axes laterally directed; width across nasal capsules 1.2 times nasobasal length of cranium (base of rostrum to occipital condyles); basal plate moderate, its minimum width about 4.5 times in nasobasal length. Antorbital cartilage sickleshaped, elongate, curved posteriorly; junction with nasal capsule relatively narrow, at posterolateral margin; its lateral extension greatly exceeding length of nasal aperture; apex bluntly pointed, margin not truncate or concave; without an anterior process. Postorbital process poorly developed, width across process 1.40 times in nasobasal length; preorbital process weak.

Pectoral skeleton with 19–20 propterygial, 7 mesopterygial, 3–4 neopterygial, 26–28 metapterygial, 56–58 total radials; anterior radials of propterygium falling slightly short of nasal capsules. Total pelvic radials 24; one greatly enlarged radial on the puboischiadic bar; 23 basipterygial radials. Vertebral column with 165 total centra (synarcual and free), 156 post-synarcual centra; 9 synarcual centra; 28 monospondylous precaudal centra, all except last two with ribs; 91 diplospondylous precaudal centra, 37 diplospondylous caudal centra.

Live coloration. Dorsal surface brownish with a scattering of pale, widely spaced spots, extending from eye to caudal fin; spots smaller than pupil of eye, often with dusky outer borders; spots paired on shoulder, above pectoral- and pelvicfin insertions, before first dorsal-fin, on anterior bases of pelvic and dorsal fins, and near free rear tip of pectoral fins. Uniformly pale ventrally; no dark markings on snout tip.

Size. To at least 582 mm TL.

Etymology. Named after the type locality of this poorly known species (i.e. the Timor Sea). Spotted shovelnose ray is the most regularly used common name.

Distribution. Timor Sea, off Melville Island (Northern Territory) at about 120 m depth.

Remarks. Members of the Australian endemic genus Aptychotrema , which are distinct from all other rhinobatids, are in need of revision as published data are limited for all species. They possess the following characters that may prove useful in defining the group: no internasal flap; deep preoral groove present; jaws strongly arched in both sexes; small, transverse nostrils with fewer lamellae and ovoid nasal capsules; anterior nasal flap inserted near posterior extremity of nostril, at margin or penetrating slightly into internarial space; posterior nasal flap extending to posterior extremity of nostril; rostral cartilages well-separated basally, constricted anteriorly; prebranchial sensory pore patch obscure, extending posteriorly to first gill slit; postscapular sensory canal long; no spiracular folds; and antorbital cartilage of chondrocranium elongate, sickle-shaped with a bluntly pointed apex and no anterior process.

This ray was first documented by Sainsbury et al. (1985) who had difficulties identifying it to a species. Its status as an unnamed taxon was initially confirmed by the author in Gloerfelt-Tarp & Kailola (1984) and later by Last & Stevens (1994). Two other nominal species, A. rostrata (Shaw & Nodder) and A. vincentiana (Haake) , are currently recognized as valid (Last & Stevens, 1994). These species, which are similar to each other in appearance, have either a plain dorsal surface or are covered by large, dusky blotches rather than white spots. One of these, A. vincentiana , is partially sympatric with A. timorensis . As well as having a more broadly rounded snout apex, A. vincentiana appears to have a relatively smaller disc (length 42–43% vs 48% TL in adults), slightly smaller orbit (interorbital width 1.1– 1.4 vs 1.0 times orbit diameter); longer tail (length 1.2–1.5 vs 1.1 times precloacal length); larger mouth (precloacal length 6.5–6.9 vs 8.0 times mouth width); longer first dorsalfin (horizontal length 7.1–7.4% vs 6.0% TL, about 1.7–2.0 vs 2.3 times in interdorsal distance); less angular dorsal-fin apices; longer caudal fin (dorsal margin 14–15% vs 12% TL); and smaller pelvic fin (length 2.3–2.6 vs 2.8 times width). Aptychotrema rostrata and A. vincentiana typically have a dark marking at the ventral apex of the snout that is lacking in A. timorensis . The smaller caudal fin of A. timorensis is evidenced by fewer vertebral centra (caudal centra 37 vs 39–44 in A. rostrata n = 9, and 42–46 in A. vincentiana , n = 18).

Figures

Fig. 1. Ventral view of the snout of the holotype of Aptychotrema timorensis n.sp. (CSIRO CA1258).

Fig. 2. Radiograph of the chondrocranium of the holotype of Aptychotrema timorensis n.sp. (CSIRO CA1258).