Aggregations of the intertidal sea-anemone Anthopleura elegantissima are formed through asexual division (longitudinal fission) of individuals. To divide, the 2 halves of an individual appear simply to crawl away from one another and, in time, to split in two. The offspring are genetically identical clones, and these often exist on the shore in large aggregations separated from one another by distinct interclonal boundaries. Fission takes between 1-8wk, and occurs generally once per year during autumn and winter when food is scarce. Clonal aggregations may take years to become established, but can persist for several decades. Sebens 1980 Biol Bull 158: 370; Sebens 1983 Pac Sci