Sea urchins are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin are distributed on the seabeds of every ocean and inhabit every depth zone from the intertidal seashore down to 5,000 meters. The spherical, hard shells (tests) of sea urchins are round and covered in spines. Most urchin spines range in length from 3 to 10 cm, with outliers such as the black sea urchin possessing spines as long as 30 cm (12 in). Sea urchins move slowly, crawling with tube feet, and also propel themselves with their spines. Although algae are the primary diet, sea urchins also eat slow-moving (sessile) animals. Predators that eat sea urchins include a wide variety of fish, starfish, crabs, marine mammals, and humans.
Orthogastropoda was a major taxonomic grouping of snails and slugs, an extremely large subclass within the huge class Gastropoda according to the older taxonomy of the Gastropoda.
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.
Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails, but also including some freshwater snails and land snails.
Loveniidae is a family of heart urchins in the order Spatangoida.
Meoma ventricosa, known by the common names cake urchin and red heart urchin, is a large species of sea urchin which lives in shallow waters in the Caribbean. It may reach a diameter of twenty centimeters and is covered in reddish-brown spines. It has both pentagonal radial symmetry and bilateral symmetry, giving it a sand-dollar appearance; however, two of its five sections are merged more closely than the others.
The taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs. The full name of the work in which this taxonomy was published is Towards a phylogeny of gastropod molluscs: an analysis using morphological characters.
Cassiduloida is an order of sea urchins. The group was extremely diverse with many families and species during the Mesozoic, but today, only seven extant species remain.
The Atelostomata are a type of sea urchins. They are distinguished from other sea urchins by their irregular shape and the absence of a feeding lantern. The group includes the well known heart urchins, as well as some less familiar and extinct forms.
Arbacioida are an order of sea urchins, consisting of a single extant family, the Arbaciidae. They are distinguished from other sea urchins by the presence of five separate plates around the anus. Unlike their close relatives, the Salenioida, all of the tubercles on their tests are of similar size.
Cidaroida is an order of primitive sea urchins, the only living order of the subclass Perischoechinoidea. All other orders of this subclass, which were even more primitive than the living forms, became extinct during the Mesozoic.
Spatangus is a genus of heart urchins in the Spatangidae family. The genus is synonymous with the previously recognised genera Prospatangus Lambert, 1902 and Spatagus. There are nine recognised species. The type species is Spatangus purpureus Müller, 1776 by subsequent designation.
The Camarodonta are an order of globular sea urchins in the class Echinoidea. The fossil record shows that camarodonts have been in existence since the Lower Cretaceous.
Spatangus purpureus, commonly known as the purple heart urchin, is a species of sea urchin in the family Spatangidae. It is found in the eastern Atlantic Ocean and the Mediterranean Sea, where it lives immersed in the sediment.
Abatus agassizii is a species of sea urchin of the family Schizasteridae. Their armour is covered with spines. It is in the genus Abatus and lives in the sea. Abatus agassizii was first scientifically described in 1889 by Georg Pfeffer.
Holasteroida is an order of irregular sea urchins.
Scutellidae is a family of sand dollars in the superfamily Scutellidea. All genera except Scaphechinus are extinct.
Irregularia is an extant infraclass of sea urchins that first appeared in the Lower Jurassic.
The Neognathostomata are a superorder of sea urchins.
Aeropsidae is a family of echinoderms belonging to the order Spatangoida. It contains one extant genus. There are also eight extinct genera, most of which fall in the subfamily Corasterinae.
