According to the classification proposed by Nitsche, and now generally adopted, the Polyzoa are divided into the two primary sections of the Entoprocta and the Ectoprocta, to which a third must be added, in accordance with the views of Dr Allman, under the name of Aspidophora, for the reception of the anomalous Rhabdopleura. The following are the principal groups of the Polyzoa:

A. Ectoprocta.

Mouth within the circle of tentacles ; anus dorsal and outside the tentacular circle; lophophore crescentic or circular.

Sub-order I. Phylactolaemata. " " II. Gymnolaemata.

B. Entoprocta.

Mouth and anus both within the circle of tentacles; lophophore horseshoe-shaped. Tentacles solid and non-retractile, filled, like the body-cavity, with parenchyma. Ectocyst not calcified. This division includes the marine Pedicellina and Loxosoma, and the fresh-water Urnatella. Loxosoma is semiparasitic, and is attached to the bodies of Gephyreans and other marine animals.