Use of traditional tools and micro-computed tomography for the taxonomy of carnivorous bivalves from the deep waters of Southwestern Atlantic

Abstract In this study, we conduct a morphological integrative analysis, using traditional techniques and micro-computed tomography imaging, on Septibranchia species. Specimens deposited in malacological collections and samples collected aboard the research vessels Puerto Deseado and Austral off Mar del Plata (~36°S), San Jorge Gulf (~46°), and Marine Protected Area Namuncurá/Burdwood Bank area (~54°S), at depths ranging from 200 to 3000 m, are the subjects of this study. Seven species were identified, including Cardiomya cleryana (d’Orbigny, 1846), Cardiomya knudseni (Allen & Morgan, 1981), Lyonsiella cf. fragilis Allen & Turner, 1974, and Cetoconcha spinulosa (Thiele, 1912), previously found in the study area. Cardiomya fragilissima (E. A. Smith, 1885), an Antarctic/sub-Antarctic species, extends its distribution up to 36°S. Two new species, Cetoconcha gigas sp. nov. and Lyonsiella tentaculata sp. nov., are described. A lectotype is designated for Pholadomya adelaidis Hedley, 1916 and a neotype for Sphenia cleryana d’Orbigny, 1846. A detailed description of the morphological characters of each species and genus, along with insights into their geographical and bathymetric distribution, are provided. The micro-computed tomography analysis of Cardiomya cleryana, Cardiomya fragilissima, and Cetoconcha spinulosa contributed to a detailed anatomical inspection and revealed the presence of muscle bundles associated with the anterior portion of the visceral mass in the scanned specimens.