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.
Linckia laevigata is a species of sea star in the shallow waters of tropical Indo-Pacific.
Culcita novaeguineae is a species of starfish. It has short arms and an inflated appearance and resembles a pentagonal pincushion. It is variable in colour and can be found in tropical warm waters in the Indo-Pacific.
Culcita is a genus of sea stars. They are found in tropical waters. Some are kept in home aquariums.
Nidorellia armata, also known as the chocolate chip star, is a species of starfish from warmer parts of the East Pacific, where it ranges from the Gulf of California to northwest Peru, including the Galápagos. It is the only species in the genus Nidorellia. N. armata can be found in tropical waters clinging on corals and rocky reefs; and are sometimes kept as pets in home marine aquariums.
Protoreaster is a genus of sea stars in the family Oreasteridae from the Indo-Pacific. They are sometimes seen in the marine aquarium trade.
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.
Archaster typicus is a species of starfish in the family Archasteridae. It is commonly known as the sand star or the sand sifting star but these names are also applied to starfish in the genus Astropecten. It is found in shallow waters in the Indo-Pacific region.
Ophiocoma scolopendrina is a species of brittle star belonging to the family Ophiocomidae. Restricted to life in the intertidal, they live in the Indo-Pacific. They can typically be found within crevices or beneath borders on intertidal reef platforms. Unlike other Ophiocoma brittle stars, they are known for their unique way of surface-film feeding, using their arms to sweep the sea surface and trap food. Regeneration of their arms are a vital component of their physiology, allowing them to efficiently surface-film feed. These stars also have the ability to reproduce throughout the year, and have been known to have symbiotic relationships with other organisms.
Fromia is a genus of starfish belonging to the family Goniasteridae.
Aquilonastra chantalae is a species of starfish from the family Asterinidae. Asterinid sea stars are typically quite small with an often pentagonal-shaped body, though there are exceptions. They are dorsally flattened and have short arms. The body's thin periphery is built up by very small marginal plates. One distinct characteristic of those in this family is the presence of an aboral face shaped by crescent-like plates.
Paracorynactis is a genus of corallimorphs from the western Indo-West Pacific. They are specialized predators of echinoderms, and are notable for preying on the destructive crown-of-thorns starfish among others. The genus is monotypic with the single species, Paracorynactis hoplites.
Heniochus pleurotaenia, the phantom bannerfish, is a marine fish belonging to the family Chaetodontidae, native from the central Indo-Pacific area.
Thelenota rubralineata is a species of sea cucumber in the family Stichopodidae, in the phylum Echinodermata, mainly located in the central Indo-Pacific region. It has a distinctive coloring pattern, and can be found on the seabed near coral. T. rubralineata is a member of the Thelenota genus, characterized by their large size and the presence of a calcareous ring.
Neoferdina cumingi, also known as Cuming's sea star, is a species of starfish in the family Goniasteridae. It is native to the tropical Indo-Pacific region.
Cenometra bella is a species of crinoids belonging to the genus Cenometra. They can have up to 30 arms and can be of variable colours but are often characterised by a marked contrast between the extending free-arms and the feathery pinnules. This species clings to its support and moves around by its feet-like cirri.
Ailsa McGown Clark (1926–2014) was a British zoologist, who principally studied echinoderms and was a specialist on asteroidea. She worked at the Natural History Museum for most of her career.
Protoreaster lincki, the red knob sea star, red spine star, African sea star, or the African red knob sea star, is a species of starfish from the Indian Ocean.
