<P> All this suggests the deuterostomes and protostomes are separate , monophyletic lineages . The main phyla of deuterostomes are the Echinodermata and Chordata . The former are radially symmetric and exclusively marine , such as starfish , sea urchins , and sea cucumbers . The latter are dominated by the vertebrates , animals with backbones . These include fish , amphibians , reptiles , birds , and mammals . </P>
distinctive characteristics of animals classified as vertebrates include
backbones