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.
A keystone species is a species that has a disproportionately large effect on its natural environment relative to its abundance. The concept was introduced in 1969 by the zoologist Robert T. Paine. Keystone species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community. Without keystone species, the ecosystem would be dramatically different or cease to exist altogether. Some keystone species, such as the wolf and lion, are also apex predators.
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.
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.
Ecological extinction is "the reduction of a species to such low abundance that, although it is still present in the community, it no longer interacts significantly with other species".
Pisaster giganteus, the giant sea star, giant spined star, or knobby sea star is a species of sea star that lives along the western coast of North America from Southern California to British Columbia. It makes its home on rocky shores near the low tide mark. It preys on mollusks. It can grow as large as 24 in (61 cm) in diameter. Its color varies from brown to red or purple.
Pisaster brevispinus, commonly called the pink sea star, giant pink sea star, or short-spined sea star, is a species of sea star in the northeast Pacific Ocean. It was first described to science by William Stimson in 1857. The type specimen was collected on a sandy bottom, 10 fathoms (18 m) deep, near the mouth of San Francisco Bay.
Pisaster ochraceus, generally known as the purple sea star, ochre sea star, or ochre starfish, is a common seastar found among the waters of the Pacific Ocean. Identified as a keystone species, P. ochraceus is considered an important indicator for the health of the intertidal zone.
Dendraster excentricus, also known as the eccentric sand dollar, sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a species of sand dollar in the family Dendrasteridae. It is a flattened, burrowing sea urchin found in the north-eastern Pacific Ocean from Alaska to Baja California.
Solaster dawsoni, the morning sun star, is a species of starfish in the family Solasteridae. It is found on either side of the northern Pacific Ocean. It has two subspecies:
Evasterias troschelii is a species of starfish in the family Asteriidae. Its common names include the mottled star, false ochre sea star and Troschel's true star. It is found in Kamchatka and the north western coast of North America.
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.
Kelletia kelletii, common name Kellet's whelk, is a species of large sea snail, a whelk, a marine gastropod mollusc in the whelk family Austrosiphonidae.
Sea star wasting disease or starfish wasting syndrome is a disease of starfish and several other echinoderms that appears sporadically, causing mass mortality of those affected. There are approximately 40 species of sea stars that have been affected by this disease. At least 20 of these species were on the Northwestern coast of Mexico to Alaska. The disease seems to be associated with increased water temperatures in some locales, but not others. It starts with the emergence of lesions, followed by body fragmentation and death. In 2014, it was suggested that the disease is associated with a single-stranded DNA virus now known as the sea star-associated densovirus (SSaDV). However, this hypothesis was refuted by recent research in 2018 and 2020. Sea star wasting disease is still not fully understood.
Lottia instabilis is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Lottiidae. Common names include the unstable limpet, the unstable seaweed limpet and the rocking chair limpet. It is native to the northern Pacific Ocean where it feeds on kelp in the intertidal zone and the shallow sub-littoral zone.
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.
Ptilosarcus gurneyi, the orange sea pen or fleshy sea pen, is a species of sea pen in the family Pennatulidae. It is native to the northeastern Pacific Ocean where it lives in deep water anchored by its base in sand or mud. It has received its common name because of its resemblance to a quill in a bottle of ink.
Lottia instabilis is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Lottiidae. Common names include the unstable limpet, the unstable seaweed limpet and the rocking chair limpet. It is native to the northern Pacific Ocean where it feeds on kelp in the intertidal zone and the shallow sub-littoral zone.
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.
