ASEXUAL REPRODUCTION BY TRANSVERSE FISSION AND SOME ANOMALIES IN THE SEA-ANEMONE NEMATOSTELLA-VECTENSIS

Nematostella vectensis is one of only 5 sea anemones known to reproduc e asexually by transverse fission. Sibling individuals of this species divide at highly variable rates with some individuals dividing rarely or not at all, while others may divide many times a year. Field popul ations are frequently unisexual, and such populations may be clones de rived from a single founder, As individual anemones grow, the asexual fragments produced do not necessarily become larger, nor is the time t aken to regenerate a functional oral crown on a fragment related to th e size of the fragment. The inclusion of a bolus of undigested food in an aboral fragment may delay completion of regeneration as compared t o fragments without a bolus. Increased food intake increases the frequ ency of fission and results in smaller fragments but does not signific antly influence the time fragments take to regenerate. Starvation supp resses fission in individuals but does not totally eliminate it. Multi -crowned anomalies are common in natural and in laboratory populations . Subsequent fission of multi-crowned individuals produces normal, sin gle-crowned anemones and meets the definition of budding, a truly rare phenomenon in sea anemones.