Zoarium, zō-ā′ri-um, n. the colony of the polypides of a polyzoan.

Most, if not all species are hermaphrodite, eggs and spermatozoa being produced either simultaneously or in succession by each individual, or by certain individuals in each zoarium.

The parent zoœcium in this formation arises from another zoœcium situated immediately behind it, so that each zoœcium, except at the extremities of the zoarium, is connected with four other zoœcia, the five together forming a cross.

Reproduction by spontaneous fission sometimes occurs, especially in the Lophopin�, but the process differs from that which takes place when a Hydra divides into two, for there is no division of individual zoœcia or polypides but merely one of the whole zoarium.

In the vast majority of the polyzoa, marine as well as freshwater, movement is practically confined to the polypide, the external walls of the zoœcium being rigid, the zoœcia being closely linked together and the whole zoarium permanently fixed to some extraneous object.