Image of Aplysiopsis enteromorphae (Eliot 1905)

Description:

Yay, another fouling slug. Found on the edge of a shell, not on its food. Since Marissa was asking about how to tell this from a nudibranch and I gave a half-assed answer, my book-reading tells me the key is the rolled rhinophores. Nudibranchs have wildly diverse rhinophores, but they're rarely (never?) simple rolls like this. Saccoglossans like this one also lack oral tentacles, which are present on many (but not all) nudibranchs, particularly the similar-looking aeolids.