Ascus (bryozoa)
The ascus is a diagnostic morphological feature of the bryozoan suborder Ascophora. It is a water-filled sac of frontal membrane opening at or near the zooid orifice. It functions as a hydrostatic system by allowing water into the space below the inflexible, calcified frontal wall when the zooid everts its polypide by muscles pulling the frontal membrane inwards.
