Description of Crisilla didyme n. sp. from the Mediterranean Sea (Mollusca, Gastropoda, Rissoidae)

A new Mediterranean species of the genus Crisilla Monterosato, 1917 (Rissooidea, Rissoidae) is described: Crisilla didyme n. sp. All known specimens come from the type locality: a submarine cave at Salina Island, Aeolian Islands, Southern Tyrrhenian Sea, Italy. It is compared with the most similar congeners from the Mediterranean Sea: Crisilla beniamina (Monterosato 1884), C. aartseni (Verduin 1984), C. ramosorum Oliver, Templado & Kersting, 2012, C. maculata (Monterosato, 1869) and from the Eastern Atlantic: C. innominata (Watson, 1897), C. postrema (Gofas, 1990) and Crisilla sp. (Romani et al., 2018). Alvania simulans Locard, 1886 is also compared with the new species, and a potential relationship with Crisilla for this species is suggested.