Abstract
Ontogenetic changes in larval photoresponses of Polyandrocarpa zorritensis (Ascidiacea, Styelidae) were studied by characterizing the swimming trajectories of individual larvae exposed to white light. The same individuals were tested repeatedly from release to settlement to remove the effects of interindividual variation in behavior. Swimming speed and overall level of activity varied significantly over time, eventually decreasing near the end of larval life. The youngest larvae swam in large spirals or straight trajectories. Late-stage larvae, used short vertical hops to contact the substratum repeatedly with the anterior papillae. This observation supports the hypothesis that papillae function in selection of a site as well as in adhesion. P. zorritensis become photopositive at the end of larval life, a behavior which probably functions in selection of microhabitats rather than in depth regulation.
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