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Ctenostomata (subphylum Ectoprocta, class Gymnolaemata) An order of bryozoans in which new individuals grow by budding from a slender, creeping tube (the stolon). The aperture of each zooid is closed by a fold of the body wall which bears bristle-like setae. The body wall is not calcified. The order first occurred in the Ordovician, and is still extant.