Any one of the cells that envelops the feeding individuals of a bryozoan colony; ectocyst: A zooecium can also be described as the stiffened body-wall which forms a cup-shaped capsule inclosing the tentacled "polypide" in the Polyzoa.

In colonial bryozoans, the body wall is a generally secreted gelatinous, chitinoid, or calcareous covering of individual zooids.

The skeleton of a zooid consists of calcareous layers of zooidal walls and connects zooidal structures.

In Phylactolaemata, the zooecium is comprised of any nonliving secreted parts of the body.