Echinoderms are exclusively marine organisms possessing spiny skin.
The phylum displays primary bilateral symmetry with both embryonic and larval stages being bilaterally symmetrical . However, when the larvae settle on the sea floor to develop into adults, the organisms become radially symmetrical . Echinoderms are usually considered as being related to the chordates . Members of both phyla show the basic characteristics of deuterostomes , with indeterminate and radial cleavage. The position of the blastopore corresponds to the position of the anus in the adult.