Labeling membrane domains in dividing echinoderm eggs.  Sea urchins have long been used as a model organism to address questions in cell biology and development. Work utilizing this model has elucidated processes of fertilization, the description of centrosomes, the separation of chromosomes during mitosis, and numerous other landmark discoveries. They have been a favorite among researchers for a variety of reasons: Eggs are large and malleable, making them relatively easy to work with; the embryos have synchronized, rapid divisions; they are easy to microinject and manipulate; and their genome sequence is available. In this Chapter, we focus on methods used to study the membrane dynamics during cytokinesis using sea urchin embryos. The focus of this chapter is to provide methods for live-cell imaging of membrane domains in sea urchin embryos.