Ascophora

Ascophora is an infraorder under order Cheilostomata of the Bryozoa. Ascophorans are distinguished from other cheilostomes in having a completely calcified wall covering their frontal surface apart from the orifice, and possessing an ascus (hence the name of the suborder). The ascus is a water-filled sac of frontal membrane opening at or near the orifice. It functions as a hydrostatic system by allowing water into the space below the inflexible frontal wall when the zooid everts its polypide (feeding tentacles) by muscles pulling the frontal membrane inwards (non-ascophorans do not need this structure as their frontal wall is not calcified).