Nectridea is an extinct order of lepospondyl tetrapods from the Carboniferous and Permian periods, including amphibious animals such as Diplocaulus. In appearance, they would have superficially resembled modern newts or aquatic salamanders, although they are not close relatives of modern amphibians (Lissamphibia). They were characterized by long, flattened tails to aid in swimming, as well as numerous features of the vertebrae.