Zooid

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).

[1] The colonial organism as a whole is called a zoon /ˈzoʊ.ɒn/, plural zoa (from Ancient Greek zôion ζῷον meaning animal; plural zôia, ζῷα).

For instance, extant bryozoans may have zooids adapted for different functions, such as feeding, anchoring the colony to the substratum and for brooding embryos.

[2] However, fossil bryozoans are only known by the colony structures that the zooids formed during life.

[4] Variations in zooid size within colonies of fossils can be used as an indicator of the temperature and the seasonality of seas in the geological past.