Zooid

File:Zooid.jpeg

Not to be confused with zoid.

A zooid or zoöid /ˈzoʊ.ɔɪd/ is a single animal that is part of a colonial animal. This lifestyle has been adopted by animals from separate unrelated taxa. Zooids are multicellular; their structure is similar to that of other solitary animals. The zooids can either be directly connected by tissue (e.g. corals, Catenulida, Siphonophorae, Pyrosome or Ectoprocta) or share a common exoskeleton (e.g. Bryozoa or Pterobranchia). The colonial organism as a whole is called a zoon /ˈzoʊ.ɒn/, plural zoa (from Greek zòon ζώον meaning animal; plural zòa, ζώα).

The term zooid has historically also been used for an organic cell or organized body that has independent movement within a living organism, especially a motile gamete such as a spermatozoon (in the case of algae now zoid), or an independent animal-like organism produced asexually, as by budding or fission.

See also

• Siphonophorae for colonial Hydrozoa which superficially resemble the other Cnidaria colloquially referred to as "jellyfish"
• Pyrosome for colonial Chordates in Tunicata