It is accomplished by muscles in the body wall of the tentacles. See if you can see the lateral cilia from this viewpoint. Look at an autozooid from the side. The gut is U-shaped with both mouth and anus located anteriorly in the vicinity of the lophophore. The mouth opens into a very short pharynx at the base of the lophophore.
Dilation is accomplished by contraction of radial muscles running from the pharynx to the body wall.
It assists in moving food particles from the lophophore into the gut. Posteriad the cardia is the thick-walled, spherical gizzard . Its epithelium bears tiny denticles, one per cell, which are thought to break the siliceous frustrules of diatoms. Zoobotryon can live and grow on a diet of diatoms but bryozoans without a gizzard, such as Bugula , cannot. Use high power to examine the gut contents looking for diatoms.