Thecate

Thecate is an adjective used in biology to describe organisms that possess a theca, a protective case, shell, or outer covering. The term derives from the Greek thekē, meaning case or envelope, and is used to distinguish organisms with a theca from those without (athecate).

In dinoflagellates, thecate species have a theca formed by plates that envelop the cell. These thecal plates create a rigid outer covering that can vary in shape and ornamentation, contributing to protection and surface properties. The contrast with athecate dinoflagellates highlights differences in cell covering within the group.

In hydrozoans, thecate hydroids refer to colonies whose polyps are enclosed by a protective theca, typically a cup-like structure formed from secreted material such as perisarc. This contrasts with athecate hydrozoans, whose polyps are not enclosed by a thecal cup.

The concept of thecate is used more broadly in biology to indicate the presence of a protective shell or covering in various lineages. The presence or absence of the theca can be important for taxonomy, description of life cycles, and interpretations of a lineage’s fossil record, ecology, and functional morphology.

See also: theca, athecate, dinoflagellates, hydrozoa.