Pavoraja Whitley

Last, Peter R. & Yearsley, Stephen Mallick And Gordon K., 2008, A review of the Australian skate genus Pavoraja Whitley (Rajiformes: Arhynchobatidae), Zootaxa 1812, pp. 1-45 : 3-4

Genus Pavoraja Whitley

Pavoraja Whitley, 1939: 254 . Type species by original designation: Raja nitida Günther, 1880 .

Definition. Small arhynchobatids with the following combination of characters: rostral shaft short, incomplete, separated from rostral base; rostral appendices short, with foramina (sometimes incomplete), widely separated from distal portion of rostral shaft; propterygia extending to rostral appendices; nasal capsules with basal fenestra; scapulocoracoid with 2–4 postventral foramina, anterior bridge absent; pseudosiphon absent; rhipidion present; dorsal terminal 3 cartilage forming spur; dorsal terminal 1 cartilage present, connected ventrally to ventral terminal cartilage; accessory terminal 1 cartilage with elongate, S-shaped distal extension forming sentinel; accessory terminal 2 cartilage with thin, disc-shaped extension forming spike; 32–47 tooth rows in upper jaw; and 25–31 monospondylous and 62–83 predorsal vertebral centra.

Description. Disc semi-oval to heart-shaped with broadly rounded outer pectoral-fin corners. Snout with small fleshy process at tip. Pelvic fins deeply incised, anterior lobe narrow and broadly rounded distally. Tail moderately elongate, slender, slightly depressed, tapering gradually. First dorsal fin subequal in height and length to second dorsal fin; dorsal fins confluent or separate; epichordal caudal-fin lobe low, separate or confluent with second dorsal fin. Anterior and posterior nasal flaps without fringes, without oronasal pits. Jaws arched slightly, not protractile. Teeth plate-like, arranged quincuncially; cusps blunt, broadly rounded; cusps sharp, pointed near symphysis in mature males.

Clasper slender, short, constricted rather than expanded at origin of glans; without dermal denticles or pseudosiphon; glans moderately expandable; inner dorsal lobe with pseudorhipidion extending from level of hypopyle to about distal one-third of glans; slit located laterally to distal portion of pseudorhipidion; spur mostly well developed; cleft medial to spur, with ribbon-like tissue in floor, passing distally from under slit to variable posterior position; rhipidion slightly pitted in texture, sometimes rotated laterally; spike disc-shaped with a sharp naked lateral margin, ventral to sentinel; distal margin of dorsal marginal truncate, with an inner extension entering glans and forming pseudorhipidion; proximal and distal margins of dorsal terminal 1 jagged; dorsal terminal 2 broad, fused to distal and disto-lateral surface of dorsal marginal (usually sutured); dorsal terminal 3 fused with dorsal terminal 2, with a distally pointed and laterally curved extension forming spur; terminal bridge absent, incomplete or slender; accessory terminal 1 Y-shaped, fused with distal surface of ventral marginal (joint unclear); accessory terminal 2 short, attached to accessory terminal 1, with a dorsoventrally flattened disc-shaped extension forming spike.

Neurocranium with rostral shaft short, slender, fused to flattened rostral node anteriorly, widely separated from rostral base and neurocranium; rostral appendices short, irregular, asymmetrical, free of rostral shaft posteriorly, often with accessory lateral cartilages, generally plate-like (when extended posteriorly becoming conical); 1–4 foramina on rostral appendices, often incomplete, anterior foramen largest; propterygia of pectoral girdle reaching rostral node; nasal capsule with basal fenestra; anterior fontanelle, interorbital region and internarial plate moderately narrow; foramen for anterior cerebral vein posterior to line connecting foramina for preorbital and orbito-nasal canals; anterior fontanelle tear-shaped; posterior fontanelle trapezoid-shaped; trochlear nerve foramen posterior and dorsal to optic nerve foramen; orbital fissure located on posterior aspect of orbit, anterior to foramen for hyomandibular branch of facial nerve and posterior to foramen of interorbital vein; jugal arches slender; single foramen for internal carotid artery; posterior cerebral vein foramen absent.

Scapulocoracoid moderately short, longer than deep, tapering slightly posteriorly; no anterior bridge; anterior fenestra subcircular to suboval, often slightly expanded dorsally, slightly smaller than posterior fenestra; posterior fenestra rounded or elongate oval; mesocondyle not expanded; neopterygial ridge incomplete; 2–4 postventral foramina.

Comparisons. Members of the genus Pavoraja (sensu McEachran, 1984) are unique within a rajoid subgroup, including putative allied genera Brochiraja (as ‘subgenus A’ in McEachran and Miyake, 1990), Irolita , Notoraja , and Pseudoraja , that form part of the tribe Arhynchobatini of McEachran and Dunn (1998). Pavoraja shares important aspects of clasper morphology with these groups (unknown in Pseudoraja ): ventral terminal cartilage lacking a sharp-edged lateral margin forming a component shield (sometimes present in Notoraja ); and the accessory terminal 2 cartilage with a disc-shaped extension forming a component spike. However, Pavoraja species have three dorsal terminal cartilages (otherwise with only dorsal terminal cartilages 1 and 2) and the tip of the dorsal terminal 3 cartilage forms a component spur.

Remarks. The new Pavoraja species conform closely with McEachran’s (1984) definition of the genus, apart from two exceptions. The number of trunk vertebral centra increased to 25–31 (from 26–29), and the tail length was found to be variable (50–64% of TL rather than slightly less or greater than 60% of TL). The scapulocoracoid is generally conservative in morphology (Fig. 2a–f), but intraspecific variability exists in at least one character (the presence of 3 postventral foramina) that was considered to be diagnostic of the genus by McEachran and Fechhelm (1982). The paratype of P. a l l e n i (figure provided with original description) has 2 equal-size postventral foramina with a smaller one centrally. Four specimens (2 of each sex) had either the configuration of the paratype, or only 2 postventral foramina with the anterior foramina slightly larger (Figs 2a, e, f); these characters were not sexually dimorphic. All other specimens of Pavoraja species examined, with the exception of P. nitida which had 4 foramina (Fig. 2d), possessed one of these configurations. Similarly, the extent of development of neopterygial ridge varies within the genus. In addition to its longitudinal extension, its level of elevation varies, and extra 1–3 small condyles are sometimes present at its posterior extremity.