The pluteus larvae of many echinoid species increase the lengths of their feeding structures in response to low food conditions. This phenotypically plastic response to the external food resource environment presents an intriguing model system for empirically testing questions related to the expression and evolution of plasticity. Answers can be found to proximate questions such as how plastic phenotypes are expressed and how the plastic responses vary among taxa and populations, as well as to ultimate questions regarding how phenotypic plasticity evolves. The pluteus system is also tractable for use in the laboratory because the organisms are small and quick-developing, are relatively robust to culture, and have long been of interest to biologists and natural historians.