Zooid
Encyclopedia
A zooid or zoöid ˈzoʊ.ɔɪd is a single animal that is part of a colonial
Colony (biology)
In biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...

 animal. The zooids can either be directly connected by tissue (e.g. corals, Catenulida
Catenulida
The Catenulida are an order of turbellarian flatworms.They are relatively small free-living flatworms, inhabiting freshwater and marine environments. The pharynx and intestine are simple in structure, with the latter forming a ciliated sac. They possess two pairs of nerve cords and often a...

, Siphonophorae or Ectoprocta) or share a common exoskeleton (e.g. Bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...

 or Pterobranchia
Pterobranchia
Pterobranchia is a clade of small, worm-shaped animals. They belong to the hemichordata, and live in secreted tubes on the ocean floor. Pterobranchia feed by filtering plankton out of the water with the help of cilia attached to tentacles. There are about 30 known living species in the group.The...

). The colonial organism as a whole is called a zoon ˈzoʊ.ɒn, plural zoa.

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
Zoid
In botany, a zoid or zoïd is a reproductive cell that possesses one or more flagella, and is capable of independent movement....

), or an independent animal-like organism produced asexually, as by budding or fission.
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