Revisiting the deep-sea Atlantic gastropod species Scaphander gracilis Watson, 1883 (Gastropoda: Cephalaspidea: Scaphandridae): first data on its anatomy, systematics, and ecology

Abstract

Scaphander gracilis Watson, 1883 is a deep-sea Cephalaspidea gastropod species endemic to the Azores in the mid-North Atlantic, and which was up to now only known from empty shells with a unique thick callus. Here, we describe for the first time the morphology of this snail species from anatomical dissections and provide a DNA barcode. A phylogeny based on the gene marker cytochrome c oxidase subunit I was inferred to test the position of S. gracilis among the genus Scaphander. In addition, the ABGD species delimitation method was employed and uncorrected p-distances were estimated. The sister relationship of S. gracilis was not resolved, but it clustered with the Atlantic species S. meridionalis and S. nobilis and the Pacific species S. grandis, S. mundus, and S. subglobosus. The smallest genetic distance was to the NE Pacific species S. grandis (4.29% in COI). Foraminifera were found in the digestive tract and the species is confirmed alive at depths between 2065−2066 m. The fact that S. gracilis was found on both sides of the Mid-Atlantic Ridge suggests that this significant geological phenomenon is not an insurmountable barrier for dispersal in this species.