INDUCTION OF METAMORPHOSIS WITH POTASSIUM-IONS REQUIRES DEVELOPMENT OF COMPETENCE AND AN ANTERIOR SIGNALING CENTER IN THE ASCIDIAN HERDMANIA-MOMUS

Increased Kt concentration in seawater induces metamorphosis in the as cidian Herdmania momus. Larvae cultivated at 24 degrees C exhibit high est rates of metamorphosis when treated with 40 mM KCl-elevated seawat er at 21 degrees C. At 24 degrees C, H. momus larvae develop competenc e to respond to KCl-seawater and initiate metamorphosis approximately 3 h after hatching. Larval trunks and tails separated from the anterio r papillae region, but maintained in a common tunic at a distance of g reater than 60 mu m, do not undergo metamorphosis when treated with KC l-seawater; normal muscle degradation does not occur in separated tail s while ampullae develop from papillae-containing anterior fragments. Normal programmed degradation of myofibrils occurs when posterior frag ments are fused to papillae-containing anterior fragments. These data indicate that H. momus settlement and metamorphosis only occurs when l arvae have attained competence, and suggest that an anterior signallin g centre is stimulated to release a factor that induces metamorphosis.