A
zooid or
zoöid is a single
animal that is part of a
colonial animal. 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 , plural
zoa (from
Greek zòon ζώον meaning animal; plural
zòa, ζώα).