A terrapin is a turtle that lives in fresh or brackish water. Taxonomy Although sometimes superficially similar to sea turtles in shape, having webbed feet and thinner shells than fully terrestrial tortoises, terrapins don't belong to the sea turtle superfamily Chelonioidea. In British English, the species most commonly referred to as terrapins are members of the family Emydidae including the red-eared slider Trachemys scripta elegans and the slider terrapin Trachemys dorbignyi. Perhaps confusi… (More on Terrapin)