Sea urchins are spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone — from the intertidal seashore down to 5,000 metres. The spherical, hard shells (tests) of sea urchins are round and spiny, ranging in diameter from 3 to 10 cm. 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. In the food chain, the predators who eat sea urchins are the sea otter and the starfish, the wolf eel, the triggerfish, and human beings.
Sand dollars are species of flat, burrowing sea urchins belonging to the order Clypeasteroida. Some species within the order, not quite as flat, are known as sea biscuits. Sand dollars can also be called "sand cakes" or "cake urchins".
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.
Astropyga radiata, the red urchin, fire urchin, false fire urchin or blue-spotted urchin, is a species of sea urchin in the family Diadematidae. It is a large species with long spines and is found in the tropical Indo-Pacific region. It was first described in 1778 by the German naturalist Nathaniel Gottfried Leske.
Rotulidae is a family of small sand dollars native to the Atlantic coast of Africa, with 3 genera, with Rotula and Heliophora being extant, the other, Rotuloidea, being extinct since the Pliocene, but all three being found in the fossil record along the Atlantic African coast since the Miocene.
Eccentric sand dollar, also known as the sea-cake, biscuit-urchin, western sand dollar, or Pacific sand dollar, is a member of the order Clypeasteroida, better known as sand dollars, a species of flattened, burrowing sea urchins found in the northeast Pacific Ocean from Alaska to Baja California.
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 cordatus is a species of sea urchin in the family Schizasteridae. It is native to shallow seas surrounding certain island groups in the southern Indian Ocean. The body is protected by a hard test or shell which is covered with spines. The female broods its young in deep pockets on the upper surface, retaining the young in place with specialised spines. American zoologist Addison Emery Verrill first scientifically described A. cordatus in 1876.
The purple sunstar, northern sunstar, or smooth sun star, Solaster endeca, is a species of starfish in the family Solasteridae.
Astropecten armatus, the spiny sand star or Estrella de Arena, is a sea star in the family Astropectinidae. It is found on sandy or gravelly areas in the East Pacific ranging from California (USA) to Ecuador.
Heliophora orbicularis, also known as the West African Sand Dollar, is a small sand dollar in to the family Rotulidae, and the only species in the genus Heliophora. It, and other members of Rotulidae have been found in West African marine strata from the Late Miocene onward. Like the related Rotula, it is still extant.
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.
Ogcocephalus notatus, the oval batfish, is a species of batfish in the family Ogcocephalidae. It is found in the tropical western Atlantic Ocean.
Clypeaster reticulatus, the reticulated sea biscuit, is a species of sea urchin in the Family Clypeasteridae. This species was first scientifically described in 1758 by Carl Linnaeus. It lives on the sandy seabed of shallow seas, semi-immersed in the sediment.
Clypeaster rosaceus, the fat sea biscuit, is a species of sea urchin in the family Clypeasteridae. It occurs in shallow water in the western Atlantic Ocean and was first scientifically described in 1758 by Carl Linnaeus.
Clypeaster humilis is a species of sea urchin in the Family Clypeasteridae. This species was first scientifically described in 1778 by the German biologist Nathanael Gottfried Leske. It occurs in the tropical Indo-Pacific region.
Echinaster callosus, the warty sea star or the banded bubble star, is a species of starfish found in shallow parts of the western Indo-Pacific region. The disc and five slender arms are covered with white, pink, red or violet warts, often forming transverse bands of colour on the arms.
Actinostella flosculifera, the collared sand anemone, is a species of sea anemone in the family Actiniidae. It is found semi-immersed in the sediment in shallow water in the tropical and subtropical Atlantic Ocean.
Echinocyamus pusillus, commonly known as the pea urchin or green urchin, is a species of sand dollar, a sea urchin in the family Fibulariidae, native to the northeastern Atlantic Ocean and the Mediterranean Sea. It buries itself in gravel or coarse sand at depths down to about 1,250 m (4,000 ft).
Luidia savignyi is a species of starfish belonging to the family Luidiidae. The species is found in the tropical and subtropical Indo-Pacific region. It is a large starfish and preys on other echinoderms.
