The phylogenetic development of the Cheilostomata has tentatively been reconstructed from the oldest, Upper Jurassic jorms, not developing heterozoecia, through the successive formation of ovicells, peristomial spines and avicularia, up to the formation of a secondary frontal wall by the development of cryptocyste or by the fusion of spines. Significant similarities in the structure of the zoecial wall of primitive Cheilostomata and Cyclostomata are stated. The hypothesis has been formed that primitive, stomatoporoidal Cyclostomata were the ancestors of the Cheilostomata. The Ctenostomata evolved also from the same forms as the Cheilostomata. A tentative biological interpretation of polymorphism and morphological gradient in a bryozoan colony has also been conducted. Seven species of the Cheilostomata have been described from the Cretaceous of Poland and a new genus, Wawalia gen.n. and a new family, Wawaliidae fam.n. have been erected.