Sub-order 3.—Cyclostomata.
Case B 2.
In the Cyclostomata, which are all calcareous, the usually tubular zoœcia have plain circular orifices without a lid or frill closing over the retracted tentacle-sheath. There are two sections in this group, viz., Articulata, in which the cells form branching colonies, the branches being connected by horny joints; and Inarticulata, in which the colonies may be encrusting, or erect and branching, but are without joints.
The first section includes the Crisiidæ.
Case B 2.
Crisia denticulata (Fig. 19) forms delicate white tufts, in which the flat slender branches are composed of a double row of tubular cells. The horny joints between the branches are black. The Inarticulata occur as crusts or branching growths. In Tubulipora flabellaris (Fig. 20) the colonies form little fan-shaped crusts on seaweeds. Lichenopora hispida forms little white disks, in which rows of tubular cells radiate from the centre. In Idmonea, the colony is branched, the tubular cells being arranged in parallel rows on each side of the middle line of the branch.
Fig. 19.
Crisia denticulata. A, natural size; B, branches magnified.
The Cyclostomata are all marine.
