Deep-sea octocorals from bathyal canyons and seamounts of the Ligurian Sea (NW Mediterranean Sea)

Abstract In recent decades, our understanding of deep-sea ecosystems has significantly improved, yet the taxonomic identity of associated species often remains understudied and this is particularly true for octocorals. This study describes the octocoral fauna inhabiting cold-water coral habitats on seamounts, canyons, and the continental slope of the Ligurian Sea (NW Mediterranean Sea), ranging from 400 to 822 m. Eighteen specimens were photographed in situ and collected using a remotely operated vehicle during two campaigns conducted in 2017 and 2021. Taxonomic analyses, based on the features of the colony, polyps, and sclerites, led to the identification of ten species. Among these, common Mediterranean bathyal species were identified, including Muriceides lepida , Villogorgia bebrycoides , Bebryce mollis , and Callogorgia verticillata . In addition, other less common species were identified, such as Acanthogorgia armata , Placogorgia coronata , and Placogorgia massiliensis . More problematic taxa included Rolandia cf. coralloides, Acanthogorgia sp., and Acanella cf. arbuscula. Each specimen is described in detail, with morphological observations complemented by high-definition images of live specimens and anatomical details. Novel insights into anatomical features, distribution patterns, and ecological preferences are presented, contributing to a more comprehensive delineation of these species. Finally, the study addresses major taxonomic challenges (including plasticity of the key anatomical characters, access to deep-sea multi-samples, and descriptions supported by high-quality images) and discusses zoogeographical and bathymetrical affinities of the Ligurian bathyal octocoral fauna.