# Operculum (bryozoa)

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In the [bryozoan](/source/Bryozoa) order [Cheilostomatida](/source/Cheilostomatida), the **operculum** is a [calcareous](/source/Calcareous) or [chitinous](/source/Chitin) lid-like structure that protects the opening through which the [polypide](/source/Polypide) protrudes.

Many species have modified the operculum in specialized [zooids](/source/Zooid) (avicularia) to form a range of [mandibles](/source/Mandible) (probably for defense) or hair-like [setae](/source/Seta) (probably for cleaning, or in some unattached species, such as *[Selenaria](https://en.wikipedia.org/w/index.php?title=Selenaria&action=edit&redlink=1)*, for locomotion[1]).

The [cyclostome](/source/Cyclostomatida) family [Eleidae](https://en.wikipedia.org/w/index.php?title=Eleidae&action=edit&redlink=1) also [convergently](/source/Convergent_evolution) evolved an opercular structure during the Early [Cretaceous](/source/Cretaceous) to [Paleocene](/source/Paleocene).[2]

## References

1. **[^](#cite_ref-1)** Cook, P.L. & Chimonides, P.J. 1987. Recent and fossil Lunulitidae (Bryozoa, Cheilostomata), 7. *Selenaria maculata* (Busk) and allied species from Australasia. Journal of Natural Historia 21: 933-966

1. **[^](#cite_ref-2)** 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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Adapted from the Wikipedia article [Operculum (bryozoa)](https://en.wikipedia.org/wiki/Operculum_(bryozoa)) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Operculum_(bryozoa)?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.