Initiation of Metamorphosis in Laboratory Cultured Sea Urchins

Many benthic marine animals release their gametes, embryos, or larvae into the water column. The offspring subsequently enter the adult population through settlement and metamorphosis. Sea urchins are one such animal. They have highly differentiated larvae that undergo a complex metamorphosis. The scant information on their metamorphosis has been reviewed by Hyman (1955). MacBride (1903) was the first to prepare a comprehensive description of metamorphosis. He used Echinus esculentus eggs that were fertilized in the laboratory. The larvae were fed on organisms collected along with the seawater in which they were raised. Earlier workers used field-collected larvae. Neither of these methods could have yielded consistently healthy and uniformly developing animals. With the development of a culture technique for sea urchins (Hinegardner, 1969), large and uniform populations of healthy animals became available for study