Tintinnids, a type of Ciliate, are common in the marine plankton. They can be identified by the presence of an outer lorica or shell. The lorica is usually cone shaped, with the narrow end closing at the top of the tube with the tip supporting the protoplast or body. Foraminifera, known primarily as fossils, are shelled protozoans with pseudopodia that are closely related to Amoebas . Radiolarians, most common in freshwater, also have a shell with spines extending out.
Protozoans feed on other organisms but also use chlorophyll, so some are a major relative of plants.