Zooidal

Zooidal is an adjective describing anything related to a zooid, the individual animal unit that forms part of a colonial organism. A zooid is produced by budding from a parent zooid and, while genetically identical to its neighbors, can be specialized for different functions such as feeding, defense, or reproduction. Colonial invertebrates often consist of many zooids that remain connected by tissues and shared bodily fluids, enabling coordinated growth and function as a single integrated unit.

In bryozoans (ectoprocts), colonies are composed of numerous zooids housed in skeletal chambers called zooecia. Most zooids are autozooids that carry the feeding apparatus, a retractable lophophore, while other zooids may be specialized for defense or reproduction. The arrangement and specialization of zooids contribute to the colony’s morphology and ecology.

In other groups, such as hydrozoans and some tunicates, colonial forms are built from zooids that may become highly specialized. In siphonophore colonies, for example, distinct zooids are adapted for swimming, feeding, or reproduction, functioning together as a single drifting organism. In corals and many anthozoans, the individual polyps function as zooids and collectively generate the reef structure.

Etymology derives from Greek zōion, animal, with the typical -oid suffix meaning “resembling” or “like.” The term is used across zoology to emphasize the modular, unit-based organization of colonial life and the functional diversity among zooids within a single colony.