''Echinocyamus pusillus'', commonly known as the pea urchin or green urchin, is a species of sand dollar, a sea urchin in the family

Fibulariidae Fibulariidae is a family of echinoderms belonging to the order Clypeasteroida Sand dollars (also known as a sea cookie or snapper biscuit in New Zealand, or pansy shell in South Africa) are species of flat, burrowing sea urchins belonging to t ...

, native to the northeastern Atlantic Ocean and the Mediterranean Sea. It buries itself in gravel or coarse sand at depths down to about .

Description

''Echinocyamus pusillus'' is a small sea urchin with a flattened, oval body up to long. The anterior end is slightly pointed. The aboral (upper) surface is convex while the oral (lower) surface is flat. The ambulacral plates widen and form a petal-like pattern on the aboral surface, and it is through each of these areas that six to nine pairs of tube feet protrude. The whole

test Test(s), testing, or TEST may refer to: * Test (assessment), an educational assessment intended to measure the respondents' knowledge or other abilities Arts and entertainment * ''Test'' (2013 film), an American film * ''Test'' (2014 film), ...

is clad in short dense spines, giving the living animal a furry appearance; spines of two types are present, relatively long, sharply-pointed ones and shorter ones with serrated tips. The mouth is in the centre of the oral surface and the anus is also on the oral surface but further back. The colour of this sea urchin is greenish or yellowish-grey, and it turns bright green if it gets injured.

Distribution and habitat

''Echinocyamus pusillus'' has a wide distribution in the northeastern Atlantic Ocean. Its range extends southwards from Iceland, Norway and Denmark to the

Azores ) , motto =( en, "Rather die free than subjected in peace") , anthem= ( en, "Anthem of the Azores") , image_map=Locator_map_of_Azores_in_EU.svg , map_alt=Location of the Azores within the European Union , map_caption=Location of the Azores wi ...

Cape Bojador Cape Bojador ( ar, رأس بوجادور, trans. ''Rā's Būjādūr''; ber, ⴱⵓⵊⴷⵓⵔ, ''Bujdur''; Spanish and pt, Cabo Bojador; french: Cap Boujdour) is a headland on the west coast of Western Sahara, at 26° 07' 37"N, 14° 29' 57"W ...

in Western Sahara, and the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ...

. It is common in the

North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea, epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the ...

and round the coasts of Britain. It occurs at depths from the lower subtidal down to about . Gravel and coarse sand provide suitable habitat in which it can bury itself.

Ecology

The spines are covered with fine, hair-like cilia, and are used to burrow or creep through the sediment while the animal searches for its food. It feeds on detritus,

Foraminifera Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly ...

, diatoms and other edible particles, moving these with its tube feet to its mouth, where they are crushed by its jaws, and the organic matter is separated from the sediment. It is often found in association with such sea urchins as '' Spatangus purpureus'' and '' Psammechinus miliaris'', the starfish ''

Asterias rubens The common starfish, common sea star or sugar starfish (''Asterias rubens'') is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 ...

'' and the brittle star '' Ophiura albida''.

References

{{Taxonbar, from=Q2034701 Clypeasteroida Fauna of the Atlantic Ocean Fauna of the Mediterranean Sea Animals described in 1776 Taxa named by Otto Friedrich Müller