Certain groups of living Chlorophyta (green algae) have thalli made up of long, tubular cells with many nuclei and many plastids (Tappan, 1980; Bold and Wynne, 1985). The only cross walls in these coenocytes are those that isolate the gamete-producing structures. As the coenocytes approach the edges of the thallus, they branch, generally dichotomously, one or more times and eventually terminate in clavate or bulbous segments called utricles (Latin for small bag or bottle). Thus, the utricles are the termini of coenocytes that occur along the surface of the thallus and interface with the environment. Utricles have been figured in many descriptions and illustrations of such calcified genera as Halimeda (Wray, 1977) and such noncalcareous genera as Codium (Bold and Wynne, 1985). Because of the easily recognized distinction between the parts of the coenocytes, the thallus in cross section consists of a cortex occupied by the utricles and their contiguous segments and a medulla occupied by the long tubular portions of the cell (Figure 1).