Catalogus

This study reports for the first time the occurrence of ragged sea hare Bursatella leachii de Blainville, 1817 in Corsica (France, NW Mediterranean Sea). The species has colonized the shallow waters (0.1–0.5 m depth) of Diana Lagoon mainly constituted of sandy-muddy bottoms and Cymodocea nodosa and Zostera noltei seagrass beds. A total of 166 individuals were inventoried in June 2023 during the survey carried out along more than 300 m of shoreline. The highest density of individuals (0.63 ind m⁻²) was mainly reported in very warm and sheltered water basins formed by the accumulation of woody debris (mean ± SE: 0.17 ± 0.06 ind m⁻²). Morphometric measurements of specimens showed an average body length of 54.3 ± 1.7 mm and weight of 14.7 ± 0.8 g. The introduction pathways of this species into this coastal lagoon may have resulted from the natural dispersal of larvae or juveniles or via the shellfish farming located in the lagoon. Extensive monitoring should be carried out along the coast of Corsica to shed light on the occurrence of the species and its spatio-temporal spread. A literature review on B. leachii has enabled us to update the existing dataset on the species distribution. The species is now confirmed from 21 out of 23 countries surrounding the Mediterranean basin.