The species Paracentrotus lividus is probably the most common species of sea urchin in the Mediterranean Sea. This species of echinoderm is included in the class Echinoidea, and within the order Camarodonta and the family Parechinidae. It inhabits the subtropical and tropical waters of temperate seas, such as the Mediterranean Sea, and in the Atlantic Ocean where it is present from the west coasts of Scotland and Ireland to the Azores, Canary Islands and Morocco. It is found either on rocky bottoms or in seagrass meadows of Zostera marina or Posidonia oceanica, and at depths of up to 90 meters.
The body is characterized by being completely circular and slightly flattened on the dorsal-ventral axis. They can reach sizes up to 7 cm in diameter. Its body is formed by a greenish calcareous skeleton, densely covered by long and pointed spines of purple, brown or olive green color. These spines sit on small semicircular abultations present on its calcareous skeleton that confer a certain degree of mobility to these spines. In addition to the spines, Paracentrotus lividus has ambulacral feet that are arranged in small groups of 5 or 6 forming arches.
It is a herbivorous species, which feeds on all types of algae, leaving the rocky surface on which they have moved completely clean of any type of algae that had previously attached. From the other point of view, it is a species whose major predators are the crab Maja crispata, the fish Diplodus sargus, Diplodus vulgaris, Labrus merula and Coris julis; the gastropod Hexaplex trunclus and the starfish Marhasterias glacialis.
The reproduction of Paracentrotus lividus occurs during the summer months. It is a species with separate sexes, although there are no external differences with which to distinguish males and females. The difference is internally in the gonads, which are yellow in the case of male specimens, and orange in females. Generally, during the breeding season, specimens are concentrated for synchronized laying. When each specimen releases its gametes into the water, fertilization occurs and a larva is formed. This larva will become part of the plankton, and approximately 1 month after its formation, it will undergo a metamorphosis process that will form a juvenile specimen that descends to the seabed.
It is worth mentioning that Paracentrotus lividus is considered a delicacy in certain countries of the Mediterranean arc, such as France, Lebanon, Italy, Spain, Malta, Greece and Croatia. In these countries the consumption of the gonads of this species is frequent. Continuing in the field of curiosities, specimens of Paracentrotus lividus have been used as an animal model in numerous studies of embryology, toxicology, physiology and biology, so it is a species very well characterized molecularly and functionally.
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