Costasiella kuroshimae, also known as "leaf slug" or "leaf sheep", is a species of sacoglossan sea slug, a shell-less marine opisthobranch gastropod mollusk in the family Costasiellidae. They can grow up to 1 cm in length.It performs kleptoplasty, which is the process of retaining the chloroplasts from the algae it feeds on so that it can use them to perform photosynthesis.
I don't really know much about leaf sheep. This is all the information Wikipedia has so enjoy some pictures