We have already described the creatures which are popularly known as Corallines. Modern zoologists have long separated off from the Corallines of the older writers, a group of animals known as the Sea-Mats, which also are colonies made up of unit individuals. The common Sea-Mat, Flustra foliacea, may be picked up on almost any part of the English coast, being often torn up "by the roots" and washed in by the tide. When fresh it has a pleasant scent, which has been compared to that of Lemon Verbena, and a pinkish colour, due to the presence of the little inhabitants in their cells. When dry it has no odour, the cells are empty, and the colour a pale drab like that of a dead Coralline. Its texture is, however, much more crisp and brittle, and less horny, than that of a dead Coralline: it grows in flat, forked expansions, much resembling in outline the fronds of several common seaweeds; and each side of these is covered with a diamond pattern of little cells. This crowded arrangement of the cells, with a tendency to assume a geometrical pattern, is the readiest feature by which the beginner may distinguish a Sea-Mat from a Coralline. The latter arrange their cells in a free-growing, tree-like or fernlike form, without any crowding of the units into a geometrical pattern. The division of the flat leaf-like colony by two, resulting in bifurcated branches, is another obvious feature of the Sea-Mat.

Covering—and to the botanist's eye disfiguring—the branches of many sea-weeds, and growing upon oyster-shells, tangle-roots, and other fixed objects, we may find many little incrustations which remind us of the lichens of the land: the diamond pattern of little cells shows us, however, that these things are relations of the Sea-Mats. The name of Bryozoa, Moss-Corals, was formerly given to these growths. Many of them bear long hair-like processes at regular intervals; these, which are large enough to be plainly seen with the naked eye, afford a ready means of recognising these creatures.

TABLE SHOWING THE CLASSIFICATION OF THE POLYZOA

The Polyzoa include freshwater as well as marine forms. They have a free-swimming larva, which becomes fixed after a time, and gives rise to the adult Colonial forms. The zooids of the latter have each an independent head with a crown of tentacles, called the Lophophore (Crest-carrier); but the fixed ends of their bodies communicate with one another. The hard covering of the colony, which retains its form after the animal is dead, is a kind of hardened skin: the apparent "cells" are the openings through which the individual zooids protrude themselves. Sometimes certain of the zooids undergo modification for special purposes: in this way are formed the "avicularia," snapping appendages, probably defensive in purpose, so called because they open and shut like a bird's beak. There are two divisions of the Polyzoa, the Ectoprocta and the Endoprocta. Among the latter there is found a form which is not colonial.

Phoronis, a curious worm-like animal, which has a larval form called Actinotrocha is sometimes placed in classification near the Polyzoa, which it resembles in possessing a crown of tentacles (Lophophore).