Fig. 20.
Tubulipora flabellaris.
a, half of an incrusting colony, × 8; b, a few cells, × 44; c, a colony, natural size.
Order II.—Phylactolæmata.
Table Case A, upright part.
All the forms in this group inhabit fresh water, where, in the form of creeping or erect branching growths or masses, they grow attached to freshwater plants, tree-trunks, old wood, etc.; two species are capable of slow movement from place to place. The lophophore and tentacular crown of the polypide are horseshoe-shaped. The Order owes its name to the presence of a lobe guarding the mouth.
In addition to the sexual, there is an asexual reproduction by means of peculiar internal buds termed statoblasts (Fig. 21). When the colony dies in the autumn, the liberated buds, securely protected in a horny capsule, retain their vitality till the spring; in due season the valves of the statoblast burst open, and the contents develope into a new colony. The statoblasts, which resemble small seeds, are usually provided with a ring of air cells, which act as a float, and in some species spines are present.
Fig. 21.
Statoblasts of Freshwater Polyzoa. A, Fredericella sultena × 38; B, Plumatella repens × 38; C, Lophopus crystallinus × 28; D, Cristatella mucedo × 28.
[‘The Cambridge Natural History.’]
Fig. 22.
A, Plumatella repens, partly free, partly incrusting stem of water-weed. B, Cells magnified. (After Allman.)
Case A, upright part.