The Southern Ocean is one of the most isolated marine ecosystems, characterized by high levels of endemism, diversity and biomass. Ascidians are among the dominant groups in the Antarctic benthic communities, thus recording the evolutionary patterns of this group is crucial to improve our current understanding on the assembly of this polar ocean. In this study, we studied the genetic variation within Cnemidocarpa verrucosa sensu lato, one of the most widely distributed and abundant ascidians in Antarctica. Using a mitochondrial and a nuclear gene (mtCOI and 18S), the phylogeography of fifteen populations distributed along the Antarctic Peninsula and South America (Burdwood Bank/MPA Namuncurá) was characterized, where the bimodal distribution of the genetic distance suggested the existence of two species within the nominal C. verrucosa. When re-evaluating morphological traits to distinguish between genetically defined species, the presence of basal disc in one of the genotypes allowed to differentiate the species.

(1) Both siphons are terminals, on the same line on the distal part (1) or one of them, oriented towards the one side (2).(2) Counts are made from the endostyle on the right side of the body (RE) to the dorsal lamina (DL) and from the DL to the endostyle on the left side (EL).(3) In general there are two gonadas to each side, but there are specimens with one gonad in each side, or two gonads in one side and one in other side of the body.

Supplement to: Ruiz, Micaela Belen; Taverna, Anabela; Servetto, Natalia; Sahade, Ricardo José; Held, Christoph (2020): Hidden diversity in Antarctica: Molecular and morphological evidence of two different species within one of the most conspicuous ascidian species. Ecology and Evolution