An echinoderm is any deuterostomal animal of the phylum Echinodermata, which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as larvae, as adults echinoderms are recognisable by their usually five-pointed radial 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.
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 1,900 species of starfish live on the seabed in all the world's oceans, from warm, tropical zones to frigid, polar regions. They are found from the intertidal zone down to abyssal depths, at 6,000 m (20,000 ft) below the surface.
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.
Tube feet are small active tubular projections on the oral face of an echinoderm, such as the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discreet though present on brittle stars, and have only a feeding function in feather stars. They are part of the water vascular system.
Intertidal ecology is the study of intertidal ecosystems, where organisms live between the low and high tide lines. At low tide, the intertidal is exposed whereas at high tide, the intertidal is underwater. Intertidal ecologists therefore study the interactions between intertidal organisms and their environment, as well as between different species of intertidal organisms within a particular intertidal community. The most important environmental and species interactions may vary based on the type of intertidal community being studied, the broadest of classifications being based on substrates—rocky shore and soft bottom communities.
Linckia laevigata is a species of sea star in the shallow waters of tropical Indo-Pacific.
Mediaster aequalis is a species of sea star in the family Goniasteridae. It is native to the west coast of North America, ranging from Alaska to California. It is found in various habitats including beaches during very low tides, and at depths down to about 500 m (1,600 ft). Also known as the vermilion sea star, it is the type species of the genus Mediaster and was first described in 1857 by the American zoologist William Stimpson.
The Asterinidae are a large family of sea stars in the order Valvatida.
Asterina phylactica is a species of sea star. It can be found in geographically widespread sites around the British Isles and in the Mediterranean Sea. It has five arms, is about 1.5 cm across and is of a green colour with central brown markings. The species was formally described in 1979 and is very similar to Asterina gibbosa.
Patiria miniata, the bat star, sea bat, webbed star, or broad-disk star, is a species of sea star in the family Asterinidae. It typically has five arms, with the center disk of the animal being much wider than the stubby arms are in length. Although the bat star usually has five arms, it sometimes has as many as nine. Bat stars occur in many colors, including green, purple, red, orange, yellow and brown, either mottled or solid. The bat star gets its name from the webbing between its arms, which is said to resemble a bat's wings.
The leather star is a sea star in the family Asteropseidae found at depths to 100 m (328 ft) off the western seaboard of North America. It was first described to science by Adolph Eduard Grube in 1857.
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.
Linckia multifora is a variously colored starfish in the family Ophidiasteridae that is found in the Indian Ocean and Red Sea. Its common names include the Dalmatian Linckia, mottled Linckia, spotted Linckia, multicolor sea star and multi-pore sea star.
The Astropecten articulatus, more commonly known as the Royal Starfish, is a West Atlantic sea star of the family Astropectinidae.
Orthasterias is a genus of sea stars in the family Asteriidae. Orthasterias koehleri, the rainbow star or red-banded sea star, is the only species in the genus. It is found in the North Pacific Ocean.
Patiria pectinifera, the blue bat star, is a species of starfish in the family Asterinidae. It is found in the northern Pacific Ocean along the coasts of Japan, China and Russia. It is used as a model organism in developmental biology.
Asterina gibbosa, commonly known as the starlet cushion star, is a species of starfish in the family Asterinidae. It is native to the northeastern Atlantic Ocean and the Mediterranean Sea.
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.
Asterina pancerii, commonly known as the seagrass asterina, is a species of starfish in the family Asterinidae. It is native to shallow parts of the Mediterranean Sea where it is usually found in seagrass meadows.
Echinoderm Research and Diversity in Latin America, edited by Juan José Alvarado, Francisco Alonso Solis-Marin Springer Science & Business Media, Aug 7, 2012 - Science
The role of Asterina stellifera (Echinodermata: Asteroidea) as a predator in a rocky intertidal community in southern Brazil. Patrícia Calil, Rosana M. da Rocha, Carolina A. Freire, James J. Roper. Zoologia (Curitiba, Impr.) vol.26 no.2 Curitiba June 2009
