A global phylogeny of <i>Elysia</i> Risso, 1818 (Gastropoda: Heterobranchia): molecular systematic insights focusing on European taxa and description of a new species

Abstract The genus Elysia comprises about one-third of the species richness in Sacoglossa. However, diversity remains poorly characterized some areas like north-eastern Atlantic and Mediterranean waters. To clarify systematics this to characterize undersampled regions, we performed an integrative study based on a thorough literature review, molecular morphological analyses, delimitation approaches. We conducted phylogenetic analyses partial sequences two mitochondrial genes (COI 16S) nuclear (H3, 28S) using Bayesian inference maximum likelihood methods, which confirmed presence five recognized European species: viridis, E. timida, flava, margaritae, rubeni. Moreover, new (Elysia azorica sp. nov.) was identified Azores, gordanae, currently considered junior synonym recovered as distinct species. In addition, consider hetta translucens taxon inquirendum. Finally, tropical evelinae is recorded along coasts for first time. Our results demonstrate value approaches resolving taxonomic uncertainty surrounding polymorphism unravelling potential cases cryptic or pseudocryptic complexes.