The avicularium (pl. avicularia) in cheilostome

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a ...

ns is a modified, non-feeding

zooid A zooid or zoöid 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 zooid ...

. The operculum, which normally closes the orifice when the zooids tentacles are retracted, has been modified to become a mandible. Strong muscles operate it. The polypide is greatly reduced, and the individual receives nourishment from neighboring zooids. The shape of the avicularian zooid can be identical to the feeding autozooid, but is usually elongated in the direction of the mandible. Avicularia are categorised by their position relative to the autozooids. Vicarious avicularia effectively replace an autozooid in the colony structure and are usually a similar size and shape as the autozooids. Interzooidal avicularia are wedged between autozooids but do not replace an autozooid. Adventitious avicularia are placed somewhere on the external (frontal) wall of an autozooid and are usually much smaller. The 'birds-head' avicularium (e.g. '' Bugula'') is elevated above the colony by a stalk (peduncle). A zooid where the operculum is modified into a very long, hair-like structure is called a

vibraculum Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Typically about long, they have a special feeding structure called a l ...

. The

cyclostome Cyclostome is a biological term (from the Greek for "round mouth") used in a few different senses: * for the taxon Cyclostomi, which comprises the extant jawless fishes: the hagfish (Myxini) and the lampreys (Petromyzontidae). This was thought for a ...

family Eleidae, which convergently evolved an opercular structure during the Early

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...

,Taylor, P.D. 1994. Systematics of the melicerititid cyclostome bryozoans; introduction and the genera ''Elea'', ''Semielea'' and ''Repromultelea''. Bulletin of the Natural history Museum, Geology Series 50:1-103 also possess avicularia-like zooids.

References

Cheilostomatida {{bryozoan-stub