A new species of the deep-sea genus Scaphander (Gastropoda, Cephalaspidea) from the Mar del Plata submarine canyon off Argentina

Abstract

Scaphander Montfort, 1810, is a genus of deep-sea, soft-bottom gastropods composed of approximately 23 species distributed worldwide. The systematics of the genus in the Atlantic was recently revised and eight species were recognized. The present study describes a new species (Scaphander meridionalis sp. n.) from the Argentine continental slope using morphological and molecular data. Shells, gizzard plates, radulae, and male reproductive systems were studied by optical and scanning electron microscopy and compared with data from all other known Scaphander species. Bayesian molecular phylogenetics based on two mitochondrial (cytochrome c oxidase subunit I and 16S rRNA) and one nuclear (28S rRNA) genes together with the molecular species delimitation method Automatic Barcode Gap Discovery were used to compare the novel samples with all known Atlantic species. Our results revealed that the Argentinian specimens have a distinct shell and penial papilla and were molecularly 6.35–6.53%, 6.9–7.44%, and 7.99–8.89% distinct (COI uncorrected p-distance) from their closest relatives, the Pacific species Scaphander grandis and Scaphander mundus, and the northern Atlantic species Scaphander nobilis, respectively. Scaphander meridionalis sp. n. is the first species only known from the South Atlantic and its occurrence off Argentina represents a new southern geographical limit of the distribution of the genus in the Atlantic Ocean.