We examined the effects of phytoplanktonic food on the survival rate, growth, development, length of larval life and competence for metamorphosis for two species of echinoids from the northeastern part of the western Mediterranean Sea. For larvae of Arbacia lixula seven diets were tested and for those of Paracentrotus lividus two. A diet of Cricosphaera elongata yielded a high survival rate (80%) and rapid larval growth; development was shorter, rudiment diameter was larger and metamorphosis rate was higher. There was a maximum feeding level beyond which no change in growth and development rate was observed. In response to a poor diet, larvae increased the larval period and the length of the larval arms; the survival rate decreased and development was slow and more variable. However, there was no change in the post-larval diameter regardless of diet history.