Echinoderms
Echinoderm is the common name given to any member of the phylum Echinodermata of marine animals. The adults are recognisable by their radial symmetry, and include such well-known animals as sea stars, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or stone lilies. - Wikipedia
Asteroidea: Starfish
Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or basket stars. Starfish are also known as Asteroids due to being in the class Asteroidea. About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, 6,000 m below the surface.
Starfish are marine invertebrates which typically have a central disc and usually five arms, although some species have a larger number of arms. The aboral or upper surface may be smooth, granular or spiny and is covered with overlapping plates.
Ophiuroidea: Brittle stars
Brittle stars, serpent stars, or ophiuroids are echinoderms in the class Ophiuroidea closely related to starfish. They crawl across the sea floor using their flexible arms for locomotion. The ophiuroids generally have five long, slender, whip-like arms which may reach up to 60 cm (24 in) in length on the largest specimens. Over 2,000 species of brittle stars live today.
Crinoids: Feather stars
Those crinoids which, in their adult form, are attached to the sea bottom by a stalk are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, being members of the largest crinoid order, Comatulida.
Holothuroidea:
Sea cumcumber
Sea cucumbers are echinoderms from the class Holothuroidea. They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. Wikipedia
Echinoidea: Sea urchin
Sea urchins, are typically spiny, globular animals, echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from the intertidal to 5,000 metres. Their hard shells are round and spiny, usually from 3 to 10 cm across. Wikipedia
