The Ctenostomata are an order of bryozoans in the class Gymnolaemata. The great majority of ctenostome species are marine, although Paludicella inhabits freshwater.
Ropalonaria venosa, an etching trace fossil of a Late Ordovician ctenostome bryozoan on a strophomenid brachiopod valve; Cincinnatian of southeastern Indiana.
They are distinguished from their close relatives, the cheilostomes, by their lack of a calcified exoskeleton. Instead, the exoskeleton is chitinous, gelatinous, or composed only of a soft membrane, and always lacks an operculum. Colonies of ctenostomes are often composed of elongated, branch-like stolons, although more compact forms also exist.