Operculum (bryozoa)

In the bryozoan order Cheilostomatida, the operculum is a calcareous or chitinous lid-like structure that protects the opening through which the polypide protrudes.

Many species have modified the operculum in specialized zooids (avicularia) to form a range of mandibles (probably for defense) or hair-like setae (probably for cleaning, or in some unattached species, such as Selenaria, for locomotion[1]).

The cyclostome family Eleidae also convergently evolved an opercular structure during the Early Cretaceous to Paleocene.[2]

References
  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
  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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