Atlantic Purple Sea Urchin

Paracentrotus 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.

Paracentrotus 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.

Archaeological evidence shows human consumption of purple sea urchins as far back as the Mousterian period of European Middle Paleolithic, where urchin remains have been in found as part of Neanderthal strata of Gibraltar's Gorham's Cave complex.

The gonads are considered a delicacy in Lebanon, France, Italy, Spain, Malta, and parts of Croatia, most notably on the island of Korčula, and are also eaten to a lesser extent in Greece and Tunisia. The urchins have been harvested for export over a wider area including Croatia, Portugal and Ireland. Additionally, sea urchin meat has been popularised in modern cuisine as "Uni", with Paracentrotus lividus being known as "Murasaki Uni". It is primarily harvested in Hokkaido, Japan alongside its counterpart "Bafun Uni".

Paracentrotus lividus is a generalist browser, eating a range of red, green and brown algae in addition to seagrass. The benthic community is much affected by the number of urchins and their food preferences. Where they are numerous they tend to be surrounded by "barren ground" colonised by encrusting Corallinaceae species and characterised by a low biomass of primary producers with a small number of associated species. Where numbers are low, there tend to be forests of Laminaria and Cystoseira and a much richer, three-dimensional community. The barren grounds can persist for years though whether this is due to overgrazing by urchins or prevention of recruitment of multicellular photosynthetic organisms by encrusting algae is unclear.