Echinoderm
Diversity

There are about 7,600 extant species of echinoderm as well as about 13,000 extinct species. All echinoderms are marine, but they are found in habitats ranging from shallow intertidal areas to abyssal depths. Two main subdivisions are traditionally recognised: the more familiar motile Eleutherozoa, which encompasses the Asteroidea (starfish, with some 1,745 species), Ophiuroidea (brittle stars, with around 2,300 species), Echinoidea (sea urchins and sand dollars, with some 900 species) and Holothuroidea (sea cucumbers, with about 1,430 species); and the Pelmatozoa, some of which are sessile while others are motile. These consist of the Crinoidea (feather stars and sea lilies, with around 580 species) and the extinct blastoids and Paracrinoids.
combination:two_responses, punctuation:no_comma