The violet sea urchin or Sphaerechinus granularis is a species that within the echinoderms we can place in the class Echinoidea, the order Camarodonta, and the family Toxopneustidae. It inhabits the waters of the eastern Atlantic Ocean, as well as the Mediterranean Sea up to 130 meters depth. It is a benthic species that prefers somewhat sheltered waters, and where it lives on rocky bottoms where there is a lot of encrusting algae, or in Posidonia oceanica meadows or gravel substrates.
Sphaerechinus granularis stands out mainly for its considerable size, a whitish appearance given by the lush tapestry of spines that cover it, and a radial symmetry that acquires an almost perfect sphericity. There are two coloration patterns, and in both cases the body color is purple. In the case of one of the variants, its spines are also purple, while the other variant has white spines. Regardless of the color of the spines, they are short, all of the same length and ending in blunt tips. The spines are arranged in neatly aligned rows along the body of the specimen. This is one of the largest urchins that diving enthusiasts can find, reaching sizes up to 15cm in diameter.
The specimens of Sphaerechinus granularis are often found semi-covered with fragments of algae, shells or other materials found on the seabed, which they keep on top of their body by means of structures called pedicellariae. These are ambulacral feet whose end has a modification in the form of small claws with which to grab these camouflage materials. It is common to find this species in association with two other species of sea urchins, such as Centrostephanus longispinus and Paracentrotus lividus.
The diet of Sphaerechinus granularis is based on algae that it gnaws from rock surfaces thanks to its beak. It has a predilection for encrusting coralline algae, as well as seagrasses and occasionally some microorganism that can live on the surfaces of these algae.
Reproduction of this species takes place throughout the year, although it is true that in the spring and early summer months is when it occurs more frequently. Both the eggs and the sperm are released into the sea for fertilization to occur and give rise to a planktonic larva that will be at the mercy of the currents. After undergoing several molts, the larva will settle to the bottom of the sea and undergo a process of metamorphosis before becoming a juvenile specimen.
As in the case of the species Paracentrotus lividus, the urchin Sphaerechinus granularis 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.Photos: