Bryozoa

The bryozoans (Bryozoa, Greek "moss animals") or ectoproctans (Ectoprocta, Gr. "external anus") are a phylum of small colonial animals, which present a lophophore, a crown of ciliated tentacles that serve to capture food, in which the anus opens outside said tentacle crown. Some 5,700 mostly marine species have been described; only about 50 live in fresh water.

For years they were classified together with the entoprocts, in which the anus opens into the tentacular corona, but the sister group of the entoprocts is now known to be Cycliophora.

Features

Sweet water Briozoo.

Like brachiopods, they are characterized by having an evaginable lophophore, a trait that places brachiopods and bryozoans within the Lophophorata clade. Its function is mainly feeding. It is a crown of tentacles that generate currents of water towards the individual's mouth. In turn, these tentacles secrete a sticky substance that favors the capture of plankton, the main diet of bryozoans, and direct it towards the mouth.

The zoetium, or protective cover, can be chitinous or calcareous, cylindrical in shape and with an opening for the exit of the polypid. This opening may or may not have an operculum.

In many groups there may be specialized zooids, giving a more advanced trait to the group. Zooids specialized in the defense of the colony are known as "avicularia". Those in charge of cleaning, "vibracularios", and those who deal exclusively with reproduction, "gonozooids".

Biology and ecology

Bryozoans filter water and feed on tiny organisms. They prefer unpolluted, still, and non-current waters, such as those in small lakes.

They form large colonies of members microscopic or nearly so. They stay on the banks when there are strong winds or activity on the lake. The name of the group ("moss animals") is due to the fact that their appearance is often reminiscent of an underwater moss cover.

The colony develops from a swimming larva, which is fixed to the substrate by means of a chitinous disc or stolon from which the first individual or ancestral develops, which by successive budding and budding gives rise to the colony or zoary. The zoo is made up of thousands of individuals or zooids that consist of two parts; the polypid (soft parts), and the zoecia (skeletal part).