<p>Many marine invertebrates have larvae that must feed to complete development to metamorphosis. Larval feeding performance affects the amount of time larvae spend in the plankton, which affects larval mortality and dispersal, and juvenile quality. Larval feeding performance is partly determined by the abundance of edible particles in the plankton. However, the plankton also contains particles that are too large for ingestion. In this thesis I show that: 1) echinoderm larval feeding performance is reduced in environmentally realistic concentrations of inedible particles in simplified laboratory feeding environments, 2) larval feeding performance of at least one echinoid is reduced in the presence of natural inedible particles in plankton, and 3) larval feeding performance may be affected by inedible beads in the mouth. My results suggest that in nature, rates of food acquisition by larvae may depend not only on food abundance, but also on the abundance of potentially interfering non-food particles.