Two new gastropods, Elysia bangtawaensis and E. siamensis from southern Thailand (Opisthobranchia, Sacoglossa, Elysiidae)

Two new Elysia species were found in brackish mangrove habitats in the southern part of the Gulf of Thailand in the area around Pattani. Elysia bangtawaensis, a large species with grooved rhinophores, was discovered living on bare mud in mangrove forests. This species looks like a fallen leaf and shows sophisticated phototrophic behaviour enabling it to survive without feeding while producing many eggs over a long period. Elysia siamensis, a small species, was found on filamentous green algae in a brackish channel. The latter species has long, thin, cylindrical rhinophores, and is further characterized by a screw-like penis, and a long thin process on the tip of its metapodium.