Naxos (Greece) Two specimen of Paracentrotus lividus: on the right a rare black specimen. The rare blacks specimens can be confused with Arbacia lixula but the white circular outline on the base of the spines are a features exclusive of P. lividus.
Naked test of Paracentrotus lividus from Agay (French Mediterranean). Frédéric Ducarme. License : CC by-sa 4.0 (https://commons.wikimedia.org/wiki/File:Paracentrotus_lividus_test.jpg?uselang=fr)