Operculum (bryozoa)


In the bryozoan order Cheilostomata, 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 to form a range of mandibles or hair-like setae.
The cylcostome family Eleidae also convergently evolved an opercular structure during the Early Cretaceous to Paleocene.