Homalozoa † Gill & Caster, 1960
Cincta †Soluta †Stylophora †Ctenocystoidea † Robison & Sprinkle, 1969Crinozoa
CrinoideaEdrioasteroidea †Cystoidea †Rhombifera †Asterozoa
OphiuroideaAsteroideaEchinozoa
EchinoideaHolothuroideaOphiocistioidea †Helicoplacoidea †Blastozoa †
Blastoidea †Cystoidea † von Buch, 1846Eocrinoidea †Jaekel, 1899Paracrinoidea † Regnéll, 1945†=Extinct
An echinoderm (/ɪˈkaɪnəˌdɜːrm, ˈɛkə-/) is any member of the phylum Echinodermata (/ɪˌkaɪnoʊˈdɜːrmətə/). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or "stone lilies". Adult echinoderms are found on the sea bed at every ocean depth, from the intertidal zone to the abyssal zone. The phylum contains about 7,000 living species, making it the second-largest grouping of deuterostomes, after the chordates. Echinoderms are the largest entirely marine phylum. The first definitive echinoderms appeared near the start of the Cambrian.
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