list of echinoderms

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list of echinoderms

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An echinoderm is any of a variety of invertebrate marine animals belonging to the phylum Echinodermata, characterized by a hard spiny covering or skin. This is a list of significant echinoderms grouped by subphylum and ordered alphabetically followed by a list of extinct echinoderms grouped alphabetically by class. (See also invertebrate.)

subphylum Asterozoa

brittle star (class Ophiuroidea)
sea star (class Asteroidea)
- crown-of-thorns starfish (Acanthaster planci)

subphylum Crinozoa

crinoid (class Crinoidea)
- feather star (order Comatulida)
- sea lily (order Bourgueticrinida)

subphylum Echinozoa

sea cucumber (class Holothuroidea)
sea urchin (class Echinoidea)
- cake urchin and sand dollar (order Clypeastroida)
- heart urchin (order Spatangoida)

extinct echinoderms

blastoid (class Blastoidea)
- genus Cryptoblastus
- genus Pentremites
carpoid (class Carpoidea)
crinoid (class Crinoidea; many extant species)
- genus Cyathocrinites
- genus Platycrinites
cystoid (class Cystoidea)
- genus Echinosphaerites
- sea urchin (class Echinoidea; many extant species)
  - genus Holectypus

This article was most recently revised and updated by Richard Pallardy.

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echinoderm

animal phylum

Also known as: Echinodermata

Written by John E. Miller, David Leo Pawson•All

Fact-checked by The Editors of Encyclopaedia Britannica

Last Updated: Apr 1, 2025 • Article History

Key People:: Alexander Agassiz

Related Topics:: carpoid; Asterozoa; Crinozoa; Blastozoa; Echinozoa

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echinoderm, any of a variety of invertebrate marine animals belonging to the phylum Echinodermata, characterized by a hard, spiny covering or skin. Beginning with the dawn of the Cambrian Period (542 million to 488 million years ago), echinoderms have a rich fossil history and are well represented by many bizarre groups, most of which are now extinct. Living representatives include the classes Crinoidea (sea lilies and feather stars), Echinoidea (sea urchins), Holothuroidea (sea cucumbers), Asteroidea (starfishes, or sea stars), Ophiuroidea (basket stars and serpent stars, or brittle stars), and Concentricycloidea (sea daisies; discovered in the 1980s).

Echinoderms have been recognized since ancient times; echinoids, for example, were used extensively by Greeks and Romans for medicinal purposes and as food. During the Middle Ages, fossil echinoids and parts of fossil crinoids were objects of superstition. In the early part of the 19th century, Echinodermata was recognized as a distinct group of animals and was occasionally associated with the cnidarians and selected other phyla in a division of the animal kingdom known as the Radiata; the concept of a superphylum called Radiata is no longer valid.

Echinoderms are separated into 21 classes, based mainly on differences in skeletal structures. The number of extant species exceeds 6,500, and approximately 13,000 fossil species have been described.

General features

Size range and diversity of structure

sea cucumberSea cucumber (*Kolga hyalina*) from the deep seafloor of the Arctic Ocean's Canadian Basin.

Although most echinoderms are of small size, ranging up to 10 cm (four inches) in length or diameter, some reach relatively large sizes; e.g., some sea cucumbers are as long as two metres (about 6.6 feet), and a few starfishes have a diameter of up to one metre. Among the largest echinoderms were some extinct (fossil) crinoids (sea lilies), whose stems exceeded 20 metres (66 feet) in length.

Echinoderms exhibit a great diversity of body forms, especially among the extinct groups. Although all living echinoderms have a pentamerous (five-part) radial symmetry, an internal skeleton, and a water-vascular system derived from the coelom (central cavity), their general appearance ranges from that of the stemmed, flowerlike sea lilies, to the wormlike, burrowing sea cucumbers, to the heavily armoured intertidal starfish or sea urchin. The general shape of the echinoderm may be that of a star with arms extended from a central disk or with branched and feathery arms extended from a body often attached to a stalk, or it may be round to cylindrical. Plates of the internal skeleton may articulate with each other (as in sea stars) or be sutured together to form a rigid test (sea urchins). Projections from the skeleton, sometimes resembling spikes, which are typical of echinoderms, give the phylum its name (from Greek echinos, “spiny,” and derma, “skin”). The surface of holothurians, however, is merely warty.

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Echinoderms also exhibit especially brilliant colours such as reds, oranges, greens, and purples. Many tropical species are dark brown to black, but lighter colours, particularly yellows, are common among species not normally exposed to strong sunlight.