Metamorphosis Is Not a New Beginning

M any marine invertebrate species have complex life cycles, in which one or more free-living developmental stages eventually metamorphoses to a morphologically-and often ecologically and physiologically-distinct juvenile stage. Such life cycles are also common among insects, amphibians, and marine fishes. Among marine invertebrates, complex life cycles are widely distributed among such diverse animals as sponges; turbellarian and trematode flatworms; gastropod and bivalved mollusks; polychaete worms; lobsters, crabs, barnacles, and other crustaceans; bryozoans; and echinoderms (Thorson 1950). Marine invertebrate larvae may feed on phytoplankton and other particulates or subsist entirely on yolk or other nutrients provided by the mother. They may spend as little as a few minutes or as long as several to many months in the plankton before metamorphosing to adult form and habitat (Pechenik 1990). Marine invertebrate larvae are