Identification and speciation of Antarctic skates

Two regions of mitochondrial (mt) DNA: cytochrome b and cytochrome c oxidase subunit 1(COI) were sequenced in 9 species of Bathyraja skates from the Southern Oceans and New Zealand. Based on significant sequence divergence, the species that has been referred to as Bathyraja eatonii from the Antarctic shelf and slope is a species distinct from B. eatonii from the Kerguelen Plateau (the type locality), and is a new and undescribed species, and should be provisionally referred to as Bathyraja n. sp. cf eatonii. There was no sequence divergence among samples of B. n. sp. “dwarf” from the Ross Sea and South Atlantic. However, for Bathyraja n. sp. cf. eatonii and Bathyraja maccaini in the Ross Sea and South Atlantic Ocean, the DNA sequence divergences are indicative of differentiation among ocean basins; and for Bathyraja n. sp. cf. eatonii are similar to divergences among recognised Bathyraja species in the North Pacific Ocean.
Despite investigating four colour characters, eight meristic characters and six morphometric characters, relatively few were diagnostic for the Antarctic Bathyraja. Ventral colouration appeared reliable for distinguishing Bathyraja meridionalis and B. n. sp. dwarf, but dorsal colouration was unreliable. Proportional disc width showed substantial changes in shape between the juvenile and adult stages of Bathyraja n. sp. cf eatonii; hence, the common name “allometric skate” is proposed. Eight meristic characters were evaluated. Pectoral radials and monospondylous vertebrae were useful in diagnosing B. n. sp. dwarf, and midline thorns for B. meridionalis. The presence/absence of thorns around the eyes and on the scapular appeared to be a reliable character to distinguish species in the Ross Sea. A field key for identification of Ross Sea skates is provided.