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 synœcium 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.
Division PLUMATELLINA, nov.
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 œsophagus 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 œsophagus. 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 zoœcium, bearing the statoblasts. Sexual organs are often absent.
Fig. 40.—Structure of the Plumatellina (after Allman).
A=a zoœcium 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=œsophagus; f=stomach; g=intestine; h=anus; j=retractor muscle; k=parieto-vaginal muscles; l=funiculus.
Two families may be recognized as constituting the division, viz., (a) the Fredericellidæ, which have a circular or oval lophophore and simple statoblast without a swim-ring, and (b) the Plumatellidæ, in which the lophophore is shaped like a horseshoe and some or all of the statoblasts are provided with a ring of air-spaces.