Valvatida

The Valvatida are an order of starfish in the class Asteroidea, which contains 695 species in 172 genera in 17 families.

Description
The order encompasses both tiny species, which are only a few millimetres in diameter, like those in the genus Asterina, and species which can reach up to 75 cm, such as species in the genus Thromidia. Almost all species in this order have five arms with tube feet. This order is primarily identified by the presence of conspicuous marginal ossicles, which characterize most of the species. Most members of this order have five arms and two rows of tube feet with suckers. Some species have paxillae and in some, the main pedicellariae are clamp-like and recessed into the skeletal plates. This group includes the cushion star, and the leather star.

Families
According to the World Register of Marine Species, the following families are included in Valvatida:


 * family Acanthasteridae Gervais, 1841
 * family Archasteridae Viguier, 1878
 * family Asterinidae Gray, 1840
 * family Asterodiscididae Rowe, 1977
 * family Asteropseidae Hotchkiss & Clark, 1976
 * family Chaetasteridae Sladen, 1889
 * family Ganeriidae Sladen, 1889
 * family Goniasteridae Forbes, 1841
 * family Leilasteridae Jangoux & Aziz, 1988
 * family Mithrodiidae Viguier, 1878
 * family Odontasteridae Verrill, 1899
 * family Ophidiasteridae Verrill, 1870
 * family Oreasteridae Fisher, 1911
 * family Podosphaerasteridae Fujita & Rowe, 2002
 * family Poraniidae Perrier, 1875
 * family Solasteridae Viguier, 1878
 * family Sphaerasteridae Schöndorf, 1906 †