Looking like opened pea pods with a lustrous sheen, the sea slugs Elysia cf. marginata and Elysia atroviridis aren’t your average gastropods. First off, they’re members of sacoglossa, a clade of slugs ...

are essentially snails without shells, terrestrial cousins of clams and oysters. They are gastropods, slime-producing mollusks that carry their stomachs inside their single “foot,” which is also their ...