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.
Protoreaster nodosus, commonly known as the horned sea star or chocolate chip sea star, is a species of sea star found in the warm, shallow waters of the Indo-Pacific region. They are sometimes seen in the marine aquarium trade or dried and sold as curios.
Ophiocanops fugiens is a living species in the brittle star family Ophiocanopidae. Though once considered to be the only one living species in this brittle star family, recent research has brought to light three specimens of Ophiocanops that differ substantially from O. fugiens. It has been regarded as the most primitive brittle star, close to Paleozoic forms, though other authors have disagreed with the view. Classification of O. fugiens is highly argued. Ophiocanops is usually placed in the order Oegophiurida or regarded as a genus incertae sedis or even given its own subclass Oegophiuridea. Some recent data suggest its relationship to the extant family Ophiomyxidae.
Ophiothrix fragilis is a species of brittle star in the order Ophiurida. It is found around the coasts of western Europe and is known in Britain as the common brittle star. It is also found along the coast of South Africa where it is known as the hairy brittle star.
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.
Amphiodia pulchella is a species of brittle star belonging to Amphiuridae, a diverse family of the Ophiurida order.
Amphiura filiformis is a species of brittle star belonging to the family Amphiuridae. It is found on the seabed in the north east Atlantic Ocean and adjoining seas to a depth of 200 metres (660 ft). It digs itself a shallow burrow in the sand and waves its arms in the water above to suspension feed on plankton.
Astroboa nuda, the naked basket star or the giant basket star, is a Gorgonocephalid basket star, a type of echinoderm. Its lengthy arms are highly branched. It inhabits reef slopes exposed to current throughout the Indo-Pacific, ranging from the Red Sea to New Caledonia. During the day, it coils into a tight ball. At night, it spreads its arms to form a basket to feed on plankton.
Gorgonocephalus arcticus is a species of basket star in the class Ophiuroidea. The genus name comes from the Greek, gorgós meaning "dreaded" and cephalus meaning "head", and refers to the similarity between these echinoids and the Gorgon's head from Greek myth with its coiled serpents for hair.
Ophiocoma echinata, the spiny ophiocoma, is a species of brittle star belonging to the family Ophiocomidae. It is the type species of the genus Ophiocoma and is found in the tropical west Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico.
Ophiactis savignyi is a species of brittle star in the family Ophiactidae, commonly known as Savigny's brittle star or the little brittle star. It occurs in the tropical and subtropical parts of all the world's oceans and is thought to be the brittle star with the most widespread distribution. It was first described by the German zoologists Johannes Peter Müller and Franz Hermann Troschel in 1842. The specific name honours the French zoologist Marie Jules César Savigny.
Ophiopholis aculeata, the crevice brittle star or daisy brittle star, is a species of brittle star in the family Ophiactidae. It has a circum-polar distribution and is found in the Arctic Ocean, the northern Atlantic Ocean and the northern Pacific.
Acrocnida is a genus of brittle stars in the family Amphiuridae. The genus contains three members: Acrocnida brachiata, Acrocnida semisquamata, and Acrocnida spatulispina. There has also been observed hybridization between both Acrocnida brachiata and Acrocnida spatulispina. It is a fairly common genus, usually found along the coasts of Northwestern Europe, but with some species like semisquamata appearing around West Africa. Members of this genus primarily prefer intertidal and sub-tidal habitats, and they are they are less likely to be found in intertidal areas by comparison. This genus was not officially classified until 1926, by T. Gislén. One study found that due to the increased calcification that Acrocnida brachiata causes could be a potential source of Carbon Dioxide for not only the warm, shallow environments they live in, but also for the atmosphere.
Ophiocomella alexandri, known as Alexander's spiny brittle star or banded brittle star, is a species of marine brittle star. It was first described to science by Theodore Lyman in 1860. Lyman states in his description that the animal is named for his friend, Alexander E. R. Agassiz, the son of Lyman's mentor, Louis Agassiz.
Amphiodia occidentalis, the long-armed brittle star, is a species of brittle star belonging to the family Amphiuridae. It is found in the Eastern Pacific coast from Alaska to USA, often on the seafloor within intertidal and subtidal zones. Within these areas, it is often found buried a few centimeters under the sand with 2 or 3 arms extending through the surface.
Ophiomastix wendtii, also known by its common name, the red ophiocoma, and formerly as Ophiocoma wendtii, is a species of brittle stars that inhabits coral reefs from Bermuda to Brazil, primarily in the Caribbean sea. These brittle stars have long, thin arms emanating from a small, disk-shaped body, and club-like spines along its arms. They are about the size of an outstretched human hand.
Ophiothela mirabilis is a species of ophiuroid brittle star within the family Ophiotrichidae. O. mirabilis is an epizoic species which have a non-parasitic relationship with host sponges or gorgonians. Although native to the Pacific Ocean, it has invaded the Caribbean and southwestern Atlantic since late 2000. Many of its characteristics, including reproduction and diet, allow O. mirabilis opportunities to quickly propagate and spread through habitats.
