Paracentrotus lividus
| Paracentrotus lividus | |
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| Paracentrotus lividus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Echinodermata |
| Class: | Echinoidea |
| Superorder: | Echinacea |
| Order: | Camarodonta |
| Family: | Parechinidae |
| Genus: | Paracentrotus |
| Species: | P. lividus |
| Binomial name | |
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Paracentrotus lividus (Lamarck, 1816) |
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Paracentrotus lividus is a species of sea urchin in the family Parechinidae commonly known as the purple sea urchin. It is the type species of the genus and occurs in the Mediterranean Sea and eastern Atlantic Ocean.
P. lividus has a circular, flattened greenish test with a diameter of up to seven centimetres. The test is densely clothed in long and sharply pointed spines that are usually purple but are occasionally other colours including dark brown, light brown and olive green. There are five or six pairs of pores on each ambulacral plate. The tube feet are in groups of 5 or 6, arranged in small arcs.
Aboral side.
Oral side (underside, with the mouth at the center).
Close-up on the spines, showing a lighter circle at the root.
Brown young.
P. lividus is found throughout the Mediterranean Sea and in the eastern Atlantic Ocean from western Scotland and Ireland to the Azores, Canary Islands and Morocco. It is most common in the western Mediterranean, the coasts of Portugal and the Bay of Biscay, where the water temperature in winter varies between 10 and 15°C.
P. lividus is usually found just below low water mark at depths down to twenty metres and sometimes also in rock pools. It is found on rocks and boulders, and in seagrass meadows of Zostera marina and Posidonia oceanica. Although Cymodocea nodosa is a preferred food item, it is seldom found in meadows of this seagrass, perhaps because the shifting sand substrate does not suit it or because of pressure from predators. In fact it avoids soft substrates and can sometimes be found clustered on stones or shell "islands" surrounded by sand. In shallow or exposed waters it can use its mouth and spines to dig into soft rocks to create cavities into which it returns and in which it exactly fits. Where the urchins are numerous, the rock may be honeycombed by these excavations. Smaller individuals particularly use these retreats, which provide some protection from predators. In lagoons and rock pools, individuals are smaller than they are in the open sea. P. lividus is unable to tolerate low salinity. After exceptional quantities of rain fell in Corsica in the autumn of 1993, there was mass mortality of urchins in the Urbini Lagoon. However the urchin is relatively unaffected by organic pollution and heavy metals, in fact it flourishes near sewage outlets. There are wide swings in population densities over its range, which have not been completely explained.
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Wikipedia