Echinoderm

Echinoderms Temporal range: Cambrian Stage 3–Present[1] PreꞒ Ꞓ O S D C P T J K Pg N
Extant and extinct echinoderms of six classes: Fromia indica (Asteroidea); Ophiocoma scolopendrina (Ophiuroidea); Stomopneustes variolaris (Echinoidea); Oxycomanthus bennetti (Crinoidea); Actinopyga echinites (Holothuroidea); Ctenocystoidea.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
Superphylum:	Deuterostomia
Clade:	Ambulacraria
Phylum:	Echinodermata Bruguière, 1791 [ex Klein, 1734]
Type genus
Echinus Linnaeus, 1758
Subphyla and classes[2]
Homalozoa † Gill & Caster, 1960 Cincta † Soluta † Stylophora † Ctenocystoidea † Robison & Sprinkle, 1969 Crinozoa Crinoidea Edrioasteroidea † Cystoidea † Rhombifera † Asterozoa Ophiuroidea Asteroidea Echinozoa Echinoidea Holothuroidea Ophiocistioidea † Helicoplacoidea † Blastozoa † Blastoidea † Cystoidea † von Buch, 1846 Eocrinoidea †Jaekel, 1899 Paracrinoidea † Regnéll, 1945 †=Extinct

An echinoderm (/ɪˈkaɪnəˌdɜːrm, ˈɛkə-/)^[3] is any deuterostomal animal of the phylum Echinodermata (/ɪˌkaɪnoʊˈdɜːrmətə/), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies".^[4] While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial symmetry (pentamerous symmetry), and are found on the sea bed at every ocean depth from the intertidal zone to the abyssal zone. The phylum contains about 7,600 living species, making it the second-largest group of deuterostomes after the chordates, as well as the largest marine-only phylum. The first definitive echinoderms appeared near the start of the Cambrian.

The echinoderms are important both ecologically and geologically. Ecologically, there are few other groupings so abundant in the biotic desert of the deep sea, as well as shallower oceans. Most echinoderms are able to reproduce asexually and regenerate tissue, organs and limbs; in some cases, they can undergo complete regeneration from a single limb. Geologically, the value of echinoderms is in their ossified dermal endoskeletons, which are major contributors to many limestone formations and can provide valuable clues as to the geological environment. They were the most used species in regenerative research in the 19th and 20th centuries. Further, some scientists hold that the radiation of echinoderms was responsible for the Mesozoic Marine Revolution.