The perimetamorphic period in Paracentrotus lividus lasts for 8-12 days. It starts from the acquisition of larval competence, includes the change in form (metamorphosis) and the endotrophic postlarval life, and stops with the appearance of the exotrophic juvenile. All major postlarval appendages already occur in competent larvae being either grouped into the echinoid rudiment (terminal plates, early spines and primary podia) or scattered within the larval integument (genital plates and sessile pedicellariae). Competent larvae show particular behaviour which brings them close to the substratum. The latter is tested by primary podia protruding through the vestibular aperture of the larva. Primary podia are sensory-secretory appendages that are deprived ampullae. They are able to adhere to the substratum in order to allow evagination of the echinoid rudiment (i.e. metamorphosis) and substatum adhesion of the postlarva. Particular spines are borne by the postlarva; these are multifid non-mobile appendages forming a kind of protective armour. Like those of the larva, all characteristic structures of the postlarva (primary podia, multified spines and sessile pedicellariae) are transitory and regress either at the end of postlarval life (primary podia) or during early juvenile life (multifid spines and sessile pedicellariae). Other appendages that develop during postlarval life (i.e. podia with ampulla, point-tipped spines and sphaeridiae) are similar to those borne by the adults and become functional when the individual enters its juvenile life. Thus, the perimetamorphic period appears to be a fully fledged period in the life-cycle of P. lividus, and presumably in the life-cycle of any other sea-urchin species.& b d y :

Soualili, D., Dubois, P., Gosselin, P., Pernet, P., and Guillou, M. 2008 Assessment of seawater pollution by heavy metals in the neighbourhood of Algiers: use of the sea urchin, Paracentrotus lividus, as a bioindicator. – ICES Journal of Marine Science, 65: 132–139. The objective of the study was to assess the levels of contamination by heavy metals near the Algiers metropolis, using a combination of chemical and toxicological data gained from analyses of sediments and biological parameters characteristic of the sea urchin, Paracentrotus lividus. Zinc, lead, cadmium, copper, and iron concentrations were determined in sediments and in sea urchin gonads. Sediment toxicity was assessed by bioassay based on the larval development of sea urchins. The most numerous larval abnormalities were found in a site near Algiers identified as highly polluted by lead. The levels of the other metals across the study area fell within the background concentrations reported in the literature for the Mediterranean Sea, with the exception of zinc, which showed high values in female gonads.

The study assessed the occurrence, possible toxicity, and impact of sediment-associated metals and PCBs in the coastal zone of the southern North Sea using echinoderms as representatives of the macrobenthos. Metals and PCBs were analyzed in the sediments and in the body compartments of the starfish Asterias rubens from 11 stations. The general toxicity of sediment-associated contaminants was assessed by bioassays using embryonic and larval developments of both A. rubens and the sea urchin Psammechinus miliaris. The impact of contamination was assessed by measuring cellular immune responses of A. rubens collected in the same stations. Contamination of the starfish by metals and PCBs closely reflected that of the sediments. However, bioaccumulation was element-specific for metals and depended on the chlorination pattern for PCBs. The sediment-associated contaminants appeared to be toxic in both the A. rubens and P. miliaris developmental assays. Moreover, metals were shown to affect the immune responses of starfishes living in contaminated stations. The most significant effects on biological responses were recorded in the plumes of the Scheldt/Rhine/North Sea Canal and the Elbe/Weser Rivers.

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No evidence for excessive thyroid cancer incidence around the Belgian nuclear power plants was found. On the other hand, an increased incidence of thyroid cancer was observed around the sites with other nuclear activities. Further research is recommended to verify whether the observed increases could be related to the site-specific nuclear activities.