Echinoderm is the common name given to any member of the
Phylum Echinodermata (from
Ancient Greek, ἐχῖνος,
echinos – "hedgehog" and δέρμα,
derma – "skin") of
marine animals. The adults are recognizable by their (usually five-point)
radial symmetry, and include such well-known animals as
starfish,
sea urchins,
sand dollars, and
sea cucumbers, as well as the
sea lilies or "stone lilies". Echinoderms are found at every ocean depth, from the
intertidal zone to the
abyssal zone. The phylum contains about 7000 living
species, making it the second-largest grouping of
deuterostomes (a superphylum), after the
chordates (which include the
vertebrates, such as
birds,
fishes,
mammals, and
reptiles). Echinoderms are also the largest phylum that has no freshwater or terrestrial (land-based) representatives.
