Arbacia lixula

Long-spined sea urchin
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Arbacia lixula from the Mediterranean
Scientific classification
Domain:	Eukarya
Kingdom:	Animalia
Phylum:	Echinodermata
Class:	Echinoidea
Order:	Arbacioida
Family:	Arbaciidae
Genus:	Arbacia
Species:	A lixula
Binomial name
Arbacia lixula (Linnaeus, 1758)

The Black Sea Urchin, Arbacia lixula is a species of Sea Urchin from Europe.

Description

File:Arbacia lixula 02.JPG

Test (shell) of a Arbacia lixula.

It is a medium-sized sea urchin, characterized by its deep black color and its haemispherical shape. All of its spines are roughly the same size (no "secondary spines"), and worn erected (never dishevelled when in the water). The anus on the top is surrounded by 4 plates forming an anal valve. The oral face is nearly naked, the mouth being surrounded by soft, dark-greenish skin.

• Arbacia lixula 03.JPG

  Profile

• Black Sea Urchin (Arbacia lixula) in Croatia.jpg

  Sticking on a rock

• Sea urchin upside down.JPG

  Oral face

• Arbacia lixula.JPG

  In situ

This species can be confused with the purple sea urchin Paracentrotus lividus, but the latter is never really black (though often very dark), has more dishevelled spines of many lengths, covers itself with debris, has spines around the mouth, no anal valve, and does not live exposed on the cliffs.

Habitat and geographical range

This species can be found on the coast of the Mediterranean Sea and Macaronesian Islands (Azores, Madeira, Canary Islands), and less commonly, on the Atlantic coast of Western Africa and the Brazilian coast. It is found typically at shallow waters, at depths from 0 to 30 m, in rocky shores. It has a good resistance to hydrodynamism due to a good attachment strength to rocks.

Biology

This species feeds mainly on crustose red algae and small filamentous algae. In a marine reserve in the Mediterranean, its population increased by a factor of over ten between 1983 and 1992, from eight individuals per square metre to a hundred individuals. It is thought that higher sea water temperatures favour this species. When it was excluded from an area of the reserve, the density of filamentous algae increased.

See also

• Arbacia spatuligera
• Echinoids Excellent photo of the test the same site.