In the larvae of the sea urchins, Lytechinus variegatus and Eucidaris tribuloides, neither the body spaces (coeloms) nor the skin (ectoderm) is directly connected to the digestive system. As there are no specific blood "vessels" in these larvae, the entire body cavity represents a circulation system. Nutrients to be delivered to these tissues must move through the body cavity from the stomach and intestine, which are the primary sites for nutrient assimilation. The motive force for material flow through the body cavity may be the cilia of a "kidney" apparatus, a derivative of the left axocoel (coelom). Originally presented in the John Wesley Powell Student Research Conference - April 17, 2004 and used with permission.