Orbiraja Last, Weigmann & Dumale, 2016, gen. nov.
Creators: name: Last, Peter R.
name: Weigmann, Simon
name: Dumale, Don
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Rajiformes
Rajidae
Orbiraja

description: Orbiraja gen. nov.
Type species. Okamejei jensenae Last & Lim, 2010.
Definition. Small to medium-sized rostrorajin skates (to about 53 cm TL) with the following combination of characters: disc rhombic, width 1–1.2 times length; snout moderately elongate, 3.9–5 times orbit length; spiracle large and broadly oval, well removed from orbit, its anteriormost margin not or barely extending forward below eye; tooth rows in upper jaw 61–76; median thorns on tail in three rows, those of outer rows usually larger than central row; procaudal length long to very long (0.9–1.4 times snout length). Clasper moderately slender and depressed, glans expanded; no dermal denticles or pseudosiphon; dorsal lobe components consisting of clefts, terminal bridge; ventral lobe components consisting of eperon, rhipidion, sentinel, shield and spike; dorsal terminal 2 cartilage long and attached to distal tip of axial cartilage (without dorsal terminal 3 cartilage); accessory terminal 1 cartilage massive rather than y-shaped with a prominent groove near its lateral margin and a slender, s-shaped distal extension through most of glans; accessory terminal 2 cartilage with a very long, curved lateral distal extension forming a component spike, and a strongly articulated, medio-distal extension (accessory terminal 3 cartilage) partly overlapping axial cartilage medially. Pectoral ocelli moderately large and almost circular; no darkedged ventral pores. Pectoral-fin radials 77–82; predorsal vertebrae 79–86; northern Indian Ocean and North-West Pacific.
Etymology. Epithet based on the Latin word orbis (meaning circle) with reference to the paired, ring-like pectoral-fin ocelli in all three nominal species. Vernacular name: Ring Skates.
Species. Orbiraja jensenae (Last & Lim, 2010) and O. powelli (Alcock, 1898). The status of O. philipi (Lloyd, 1906) needs to be reassessed as it has been considered a possible junior synonym of O. powelli (Weigmann et al., 2015; Weigmann, 2016). New material of O. powelli collected off Myanmar suggests that this species is morphologically variable, including the shape of the pectoral marking. Lloyd’s original figure of the type has the pectoral marking placed more posteriorly on the disc than in typical O. powelli. Preliminary investigations indicate that an additional, un-named species of Orbiraja occurs off Indonesia.
Remarks. A substantial body of literature has been assembled on the clasper morphology of skates, but no comprehensive coverage of all extant genera has been published and details of the adult clasper are unknown for some genera (e.g. Pseudoraja). Orbiraja resembles Okamejei in external morphology, but members of these genera differ from each other in clasper morphology, squamation and in their molecular sequences. In Orbiraja there are 3 well-developed rows of thorns along the middle of the tail and these are positioned unusually close together and well away from the lateral thorn rows. Some Okamejei (e.g. O. kenojei) have three prominent thorn rows along the median tail but these are well separated (lateral-most rows usually dorsolateral in position). Okamejei species also have dark-edged pores on the ventral head compared to not being dark-edged in Orbiraja. The claspers of the Okamejei species have a component funnel (absent in Orbiraja and Okamejei ornata Weigmann, Stehmann & Thiel) and the ventral terminal cartilage is claw shaped (not claw-shaped in Orbiraja). Neither Okamejei nor the other rostrorajin genera (Malacoraja, Neoraja and Rostroraja) are known to have an accessory terminal 3 cartilage (arising from the disto-medial margin of the accessory terminal 2 cartilage); an accessory terminal 3 cartilage is present in the ‘amphi-American assemblage’ but is located on the disto-lateral extension of the dorsal marginal cartilage (J. McEachran, pers comm.). The position of the spiracles relative to the eyeball in Orbiraja is somewhat unusual within skates (placed more posteriorly) and needs further exploration. The orbit + spiracle length is 1.7– 2.0 times the orbit diameter in Orbiraja jensenae versus 1.2–l.6 times in several rajin skates examined (PL, unpubl.).
description: Published as part of Last, Peter R., Weigmann, Simon & Dumale, Don, 2016, A new skate genus Orbiraja (Rajiformes: Rajidae) from the Indo-West Pacific in Zootaxa 4184 (1), DOI: 10.11646/zootaxa.4184.1.3, http://zenodo.org/record/164475