Squalus rancureli Fourmanoir, 1979, a new junior synonym of the blacktailed spurdog S. melanurus Fourmanoir, 1979, and updated diagnosis of S. bucephalus Last, Séret & Pogonoski, 2007 from New Caledonia (Squaliformes, Squalidae)

Squalus rancureli Fourmanoir, 1979 and S. melanurus Fourmanoir, 1979 are deep-sea sharks described from off New Caledonia and Vanuatu. Morphological separation between them is limited to caudal fin coloration and a few morphometric characters. These two nominal species were described as new in more than one taxonomic account, thus requiring nomenclatural elucidation. Taxonomic complexity behind S. rancureli and S. melanurus has been disregarded and underestimated in previous studies, and indicated to rely on propagation of erroneous authorship and negligence of requirements from the International Code on Zoological Nomenclature for describing new taxa. Analysis of type material and topotypic specimens revealed congruency of external morphology, external measurements and meristic data, suggesting conspecificity. Squalus rancureli is herein considered a junior synonym of S. melanurus, and authorship of these nominal species is clarified. Differential diagnosis and redescription of S. melanurus and an updated diagnosis of S. bucephalus Last, Séret & Pogonoski, 2007 are also provided based on new material. Comparative examinations with other regional congeners support their validity and recognition of a third species provisionally identified as Squalus cf. montalbani. Squalus melanurus is easily distinguished from S. bucephalus Last, Séret & Pogonoski, 2007 by bearing a black caudal-fin lower lobe, snout conspicuously elongate, dermal denticles tricuspidate, and smaller number of vertebrae (vs whitish caudal-fin lower lobe, snout conspicuously short, dermal denticles unicuspidate, higher number of vertebrae).