A class of Bryozoa confined to fully marine water. The Stenolaemata include several thousand species distributed among four orders: Cystoporata, Trepostomata, Cryptostomata, and Cyclostomata (=Tubuliporata). The commonly recognized order Fenestrata likely is part of the Cryptostomata. First appearing late in the Early Ordovician, stenolaemates expanded quickly to dominate bryozoan assemblages through the Early Cretaceous. By mid-Cretaceous, the calcified gymnolaemate order Cheilostomata, which originated in the Late Jurassic, had increased in diversity and abundance to equal that of stenolaemates, eventually surpassing the stenolaemates, which are now a minor part of the bryozoan fauna in most marine environments.