Coelomocytes (blood cells) of the solitary ascidian Halocynthia roretzi were observed in culture by phase-contrast, time-lapse video and scanning electron microscopy. Seven types and one sub-type of cells were distinguished with respect to their morphology and behavior. These cell types are discussed in relation to those appearing in the literature. A table of correlation between cells reported under various names in the literature is presented in the ^Appendix.