Why are zooid features more useful than colony shape for classifying bryozoans?

Zooidal features are generally considered more reliable than colony shape for classifying bryozoans because colony forms are often ill-defined and lack a consistent, individualistic structure. Colonies can grow in various directions and are frequently subject to environmental influence, making them less stable indicators for taxonomy.12

In contrast, the specific skeletal and morphological features of individual zooids provide more consistent diagnostic criteria. For example, in cheilostomes, the structure of the frontal wall, the shape of the orifice, the type of brood chambers (ooecia), and the presence of specialized zooid types (polymorphism) are critical for identification. While colony form remains important for groups that lack skeletal features—such as ctenostomes and phylactolaemates—zooidal characters remain the primary standard for classification across the phylum.1