All the phylactolæmata produce the peculiar reproductive bodies known as statoblasts.
The phylactolæmata, which are probably descended from ctenostomatous ancestors, are confined to fresh or slightly brackish water. Most of the genera have a wide geographical distribution, but (with the exception of a few statoblasts of almost recent date) only one fossil form (_Plumatellites_, Fric. from the chalk of Bohemia) has been referred to the order, and that with some doubt.
It is convenient to recognize two main divisions of the phylactolæmata, but these divisions hardly merit the distinction of being regarded as suborders. They may be called Cristatellina and Plumatellina and distinguished as follows:--
Division I, PLUMATELLINA, nov.--Ectocyst well developed; zoaria without a special organ of progression; polypides contained in tubes.
Division II, CRISTATELLINA, nov.--Ectocyst absent except at the base of the zoarium which is modified to form a creeping "sole"; polypides embedded in a common synoecium of reticulate structure.
The Cristatellina consist of a single genus and probably of a single species (_Cristatella mucedo_, Cuvier), which is widely distributed in Europe and N. America, but has not been found in the Oriental Region. Eight genera of Plumatellina are known, and five (possibly six) of these genera occur in India.
The structure of the species included in this division is very uniform as regards the internal organs (see fig. 40 opposite and fig. 47 _a_, p. 236). The alimentary canal is simpler than that of the Paludicellidæ. A short oesophagus leads directly into the stomach, the cardiac portion of which is produced as a vertical limb almost cylindrical in form and not constricted at the base. This limb is as a rule of greater length than the oesophagus. The pyloric part of the stomach is elongated and narrow, and the intestine short, straight, and of ovoid form. There are no cilia at the pyloric opening. A single funiculus joins the posterior end of the stomach to the wall of the zooecium, bearing the statoblasts. Sexual organs are often absent.
[Illustration: Fig. 40.--Structure of the Plumatellina (after Allman).
A=a zooecium of _Fredericella_ with the polypide extruded. B=the lophophore of _Lophopus_ (tentacles removed) as seen obliquely from the right side. C=larva of _Plumatella_ as seen in optical section. _a_=tentacles; _b_=velum; _c_=epistome; _d_=mouth; _e_=oesophagus; _f_=stomach; _g_=intestine; _h_=anus; _j_=retractor muscle; _k_=parieto-vaginal muscles; _l_=funiculus.]