ABSTRACT
Echinocardium cordatum is found littorally and infralittorally in the Bay of Seine. Four unevenly distributed size classes characterize the population. Three are exclusively infralittoral and the fourth littoral. The littoral settlement results from shoreward migration of infralittoral individuals. Migrating individuals are mostly two to four years old. The littoral settlement combines individuals that are probably more than four years old. The large size of the littoral individuals is interpreted in terms of age and better growth conditions on the shore.
