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 reproduce 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 populations are frequently unisexual, and such populations may be clones derived from a single founder. As individual anemones grow, the asexual fragments produced do not necessarily become larger, nor is the time taken to regenerate a functional oral crown on a fragment related to the size of the fragment. The inclusion of a bolus of undigested food in an aboral fragment may delay completion of regeneration as compared to fragments without a bolus. Increased food intake increases the frequency of fission and results in smaller fragments but does not significantly influence the time fragments take to regenerate. Starvation suppresses 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, single-crowned anemones and meets the definition of budding, a truly rare phenomenon in sea anemones.