The new Checklist of the Italian Fauna: Ascidiacea

We present a data set reporting the checklist of the species belonging to the class Ascidiacea for the 9 Italian marine biogeographical units, updating the one previously published by Mastrototaro & Tursi in 2010. In detail, the updated checklist includes 138 taxa at species level (66 Aplousobranchia, 30 Phlebobranchia and 42 Stolidobranchia). Records refer to various marine habitats, including lagoons, harbours and semi-enclosed environments as well as deep habitats. The previous checklist reported 129 taxa (66 Aplousobranchia, 27 Phlebobranchia and 36 Stolidobranchia): in detail, 12 species were added, of which four newly described species, seven non-indigenous species and a new record for the Italian waters. On the other hand, three species reported in the previous checklist were removed: two because currently considered dubious, and one because its occurrence in the Mediterranean Sea is not actually confirmed. Finally, two species were renamed because they are considered synonyms of older ones and five species are currently accepted with new combinations. In addition, five species expanded their biogeographic distribution. The checklist data set will be dynamically updated with new records, and it will be freely available from Lifewatch Italy at https://www.lifewatchitaly.eu/en/initiatives/checklist-fauna-italia-en/checklist. This note describes the state of the art of the Ascidian checklist data set until February 2022. &nbsp