While some rhodophytes are unicellular, most species grow as filaments, such as those shown below at right, or membranous sheets of cells. Some of these multicellular forms are coralline, depositing skeletons composed of calcium carbonate crystals within and around their cell walls. These calcified reds can be difficult to distinguish from corals without the assistance of a microscope or a trained eye, as you can see from the picture below at left.
The red "algae" lack flagella at all stages in their life history, and cells may be multinucleate.