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Why is Cheilostomata considered the most successful bryozoan group?

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Eurystomella bilabiata, a moss animal from the Order Cheilostomata. — moss animal *Eurystomella bilabiata*, a moss animal from the Order Cheilostomata.

The Cheilostomata are considered the most successful group of bryozoans primarily because they are the most abundant and varied of all modern species, comprising approximately 2,800 described species and 600 genera.12

Their success is attributed to their evolutionary adaptations, which provided superior protection compared to earlier forms. While early cheilostomes had simple calcified side walls, the later evolution of the Ascophora (ascus bearers) in the Late Cretaceous allowed them to calcify their front walls while maintaining the hydrostatic function necessary to evert their feeding apparatus, the lophophore. This development, combined with the presence of a lidlike structure called an operculum that protects the individual zooids, allowed them to thrive in diverse marine environments.123