Abrupt change in food environment induces cloning in plutei of Dendraster excentricus.  Asexual reproduction, or cloning, of planktonic echinoderm larvae has been observed in the laboratory and in nature, but little is known about its ecology. Here we examine the effects of algal food density and of a change in food density on the incidence of cloning in larvae of the sand dollar Dendraster excentricus. Results indicate that a change in food concentration can induce cloning in plutei. Cultures transferred from a low to a high algal ration at the time when primary larvae were developing the third (posterodorsal) pair of larval arms showed decreased postoral arm length, unusual morphologies, and increased larval density in culture. These dense cultures of smaller plutei were produced within 48 h of the food pulse. The result is consistent with the occurrence of a burst of cloning, possibly through anterior autotomization. A second feeding experiment demonstrated that anterior autotomization does occur in 4- to 6-arm plutei. Rather than constituting a developmental rarity, cloning may happen early and often in D. excentricus cohorts when environmental conditions favor rapid growth.