The avicularium (pl. avicularia) in cheilostome bryozoans is a modified, non-feeding zooid. Cheilostomata, an order under class Gymnolaemata, are exclusively marine colonial invertebrate animals Bryozoans are tiny colonial Animals that generally build stony Skeletons of Calcium carbonate, superficially similar to Coral (although some The operculum, which normally closes the orifice when the zooids tentacles are retracted, has been modified to become a mandible. In the Bryozoan order Cheilostomata, the operculum is a Calcareous or chitinous lid-like structure that protects the opening through which the Strong muscles operate it. The polypide is greatly reduced, and the indiviual receives nourishment from neighboring zooids. The polypide in Bryozoans encompasses most of the organs and tissues of each individual zooid 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. Bulgula) 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.
The cylcostome family Eleidae, which convergently evolved an opercular structure during the Early Cretaceous to Paleocene [1], also possess avicularia-like zooids. Cyclostomatida, or cyclostomes are an ancient order of Stenolaemate Bryozoans which first appeared in the Lower Ordovician. Convergent evolution describes the acquisition of the same biological trait in unrelated lineages The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of The Paleocene or Palaeocene, "early dawn of the recent" is a geologic epoch that lasted from 65
References
- ^ 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
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