The zoœcia are provided neither with a lip nor with a collar-like membrane. They are tubular and usually have circular orifices.
The Cyclostomata are exclusively marine.
Ectoproctous polyzoa the polypides of which have a leaf-shaped organ called an epistome projecting upwards and forwards within the circle of tentacles and between the mouth and the anus. The zoœcia are not distinct from one another, but in dendritic forms the zoarium is divided irregularly by chitinous partitions.
The Phylactolæmata are, without exception, freshwater species.
II.
Synopsis of the Leading Characters of the Divisions of the Suborder Ctenostomata.
Suborder B. CTENOSTOMATA.
The suborder has been subdivided in various ways by different authors. The system here adopted is essentially the same as that proposed in a recent paper by Waters (Journ. Linn. Soc. London, Zool. xxi, p. 231, 1910), but I have thought it necessary to add a fourth division to the three adopted by that author, namely, the Alcyonellea, Stolonifera, and Vesicularina. This new division includes all the freshwater genera and may be known as the Paludicellina. In none of these divisions are the tentacles webbed at the base.
The four divisions may be recognized from the following synopsis of their characteristic features:—