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Fishery and Sea ResourcesFigure 1: The sea urchin Paracentrotus lividus: adult sea urchin (A); adult immune cells(coelomocytes), in focus red and white amoebocytes (B); embryo at the pluteus stage(C); 8-arms larva with rudiment (D) indicated by the yellow arrow, and the intestine as aspherical shaped structure of a yellowish color, consequence of the brown algae ingested;juvenile (E). The sea star Asteria rubens: adult sea star (F); section of amputated arm (G),in blue coelomic epithelium.satisfy the following conditions: 1) plentifulin number in the wild; 2) broadly availablein the marine environment; 3) ecologicallyrelevant; 4) easily manageable inlaboratory experiments. The ideal modelorganism can then be used for a numberof purposes: 1) to analyze toxicity of environmentalhazards and chemical pollutants;2) to elucidate the mechanism oftheir toxic action at various biological levels(i.e. population, whole organisms, cellularand molecular); 3) to understand howmarine organisms cope with toxicants andrespond to them at the physiological orbiochemical levels. Furthermore, an idealmodel organism is also of great importancefor the development of standardized alternativebiomolecular ecotoxicological tests.Among marine organisms, echinodermsare highly sensitive to physical and/orchemical environmental changes occurringin the sea water ecosystems where theylive. They are among the most familiar marineinvertebrates, characterised by a greatmorphological variety of their members,some of them being very popular and fascinatingfor their shapes (sea urchins) andcolours (sea stars). Conditions for success-1968