How many seas must a nudibranch sail? Okenia picoensis (Mollusca: Nudibranchia: Goniodorididae) conquering the Mediterranean

The genus Okenia is undergoing a singular evolution in the last 20 years, with the description of new species and the rapid diffusion into new biogeographical compartments. Described only in 2017, from specimens collected in 2013 at the Azores islands, Okenia picoensis in the span of five years has been observed in the Mediterranean from east to west and north in the Gulf of Lion. The first observations for Sardinia are reported here and its current diffusion is mapped, mainly based on data mining, and discussed.