<i>Botryllus</i> (Ascidiacea, Styelidae) on the Argentine coast

Two species belonging to the genus <i>Botryllus</i> from three localities (five sampling sites) on the Argentine coast (southwestern Atlantic) were identified, based on morphological analyses. Besides, genetic analyses (COI partial sequences) revealed the presence of clade A of the <i>Botryllus schlosseri</i> species complex, which is widely distributed and considered invasive, in Mar del Plata and Puerto Madryn localities. In addition, a species never detected in the study area was recorded: <i>Botryllus planus</i> with a tropical distribution in the western Atlantic and considered cryptogenic in Brazil. The present study emphasises the need to make morphological diagnoses and generate species barcodes to help identify clades or cryptic species and contribute to the genetic database of the different species. Accurate species identification enables the delimitation of their distribution areas. Their occurrence in natural or artificial habitats (e.g. harbours, marinas, shipwrecks) provides insights into their biogeographic status in the area.