In biology, a lorica is a shell-like protective outer covering, often reinforced with sand grains and other particles that some protozoans and loriciferametazoans secrete. Usually it is tubular or conical in shape, with a loose case that is closed at one end.  An example is the protozoan genus Stentor, in which the lorica is trumpet-shaped. In the tintinnids, the lorica is frequently transparent and is used as domicile.Halofolliculina corallasia has a lorica that is attached as an outer structure, and into which it retracts when disturbed.
There are three phases in the formation of lorica: agglomeration in a natural cast; helical extension; and stabilization.