thecae

Thecae are sheath-like structures found in a range of organisms and tissues; the term derives from Latin theca, meaning case or sheath. In biology the plural form thecae is used for several distinct concepts.

In plants, the thecae are the pollen sacs of anthers. Each anther lobe typically contains two thecae, separated by a connective tissue. The sac houses pollen grains, and dehiscence releases the pollen when the stomium opens. The number and arrangement of thecae vary by species and influence pollen release.

In zoology, theca describes an external protective covering in several groups. In bryozoans, theca refers to the rigid exoskeleton that surrounds each zooid; it is secreted by the epidermis and forms the colony’s protective housing. In some protozoans and dinoflagellates, thecal plates form thetheca, a cellulose-based or calcified outer layer that defines cell shape and rigidity; the arrangement of plates (thecal pattern) is species-specific and used in taxonomy.

In mammalian reproductive biology, theca refers to the theca interna and theca externa of ovarian follicles. The theca externa is a fibrous layer enclosing the follicle; theca interna consists of steroidogenic cells that respond to luteinizing hormone and synthesize androgens, which diffuse to granulosa cells to be aromatized into estrogens. The theca contributes to follicle growth and ovulation and plays a role in luteinization after ovulation.

Across contexts, the term theca therefore denotes a sheath or covering, with functional specialization from protective exoskeletons to hormone-producing ovarian layers.