In biology, a lorica is a shell-like protective outer covering, often reinforced with sand grains and other particles that some protozoans and loricifera

Loricifera

Loricifera is a phylum of very small to microscopic marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more that have been collected and not yet described. Their size ranges from 100 µm to ca....

 metazoans 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

Stentor (protozoa)

Stentor, sometimes called trumpet animalcules, are a genus of filter-feeding, heterotrophic ciliate protists, representative of the heterotrichs...

, in which the lorica is trumpet-shaped. In the tintinnid

Tintinnid

Tintinnids are ciliates of the choreotrich taxon Tintinnida, distinguished by vase-shaped shells called loricae, which are mostly protein but may incorporate minute pieces of minerals. Although appearing as early as the Ordovician period, tintinnids became abundant in the fossil record during the...

s, the lorica is frequently transparent and is used as domicile. Halofolliculina corallasia

Halofolliculina corallasia

Halofolliculina corallasia is a heterotrich ciliate identified as a cause of the syndrome called Skeletal Eroding Band . It is the first coral disease pathogen that is a protozoan as well as the first known to be an eucaryote; all others identified are bacteria...

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

Casting

In metalworking, casting involves pouring liquid metal into a mold, which contains a hollow cavity of the desired shape, and then allowing it to cool and solidify. The solidified part is also known as a casting, which is ejected or broken out of the mold to complete the process...

; helical extension; and stabilization.