An echinoderm is any member of the phylum Echinodermata. The adults are recognisable by their 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.
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.
Echinocardium cordatum, also known as the common heart urchin or the sea potato, is a sea urchin in the family Loveniidae. It is found in sub-tidal regions in the NE Atlantic. Other un-named species have been identified as this species from temperate seas around the world. It lives buried in the sandy sea floor.
Ophiura ophiura or the serpent star is a species of brittle star in the order Ophiurida. It is typically found on coastal seabeds around northwestern Europe.
Luidia ciliaris, the seven-armed sea star, is a species of sea star (starfish) in the family Luidiidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea.
Ophiocomina nigra, commonly known as the black brittle star or black serpent star, is a species of marine invertebrate in the order Ophiurida. It occurs in the north-eastern Atlantic Ocean, the North Sea and the Mediterranean Sea.
Ophiura albida is a species of brittle star in the order Ophiurida. It is typically found on the seabed in the north eastern Atlantic Ocean and in the Mediterranean Sea and is sometimes known as the serpent's table brittle star.
Amphipholis squamata, common names brooding snake star and dwarf brittle star, is a species complex of brittle stars in the family Amphiuridae.
Luidia maculata is a species of starfish in the family Luidiidae in the order Paxillosida. It is native to the Indo-Pacific region. It is commonly known as the eight-armed sea star because, although the number of arms varies from five to nine, eight arms seems to be the most common.
Amphiura chiajei is a species of brittle star belonging to the family Amphiuridae. It is found in the northeastern Atlantic Ocean and adjoining seas to a depth of 1,000 metres (3,300 ft). It digs itself into the soft sediment of the seabed and raises its arms into the water above to suspension feed on plankton. It was first described by the British naturalist Edward Forbes in 1843, and was named for the Italian zoologist Stefano Delle Chiaje (1794–1860).
Luidia magellanica is a species of starfish in the family Luidiidae. It is found in the southeastern Pacific Ocean on the coast of South America.
Acrocnida brachiata, the sand burrowing brittlestar, is a species of brittle star in the family Amphiuridae. It occurs on the seabed in the northeastern Atlantic Ocean and the North Sea, living semi-buried in the sand with only its arm tips projecting.
Thyone fusus is a species of sea cucumber in the family Phyllophoridae. It is found on the seabed in the northeastern Atlantic Ocean and the Mediterranean Sea. It is a suspension feeder and catches food particles floating past with its branching feeding tentacles.
Echinocardium flavescens, sometimes called the yellow sea potato, is a species of sea urchin in the family Loveniidae, chiefly found in the northeast Atlantic region.
