Bryozoa ("Moss animals") are tiny creatures with a ring of tentacles surrounding the mouth. The phylum Bryozoa has been divided into several phyla that are quite likely unrelated: the Ectoprocta, the Entoprocta, and the Cycliophora. Almost always the first of the three is meant. Bryozoans can be further divided into 2 main classes: the Stenolaemata and the Gymnolaemata.

Bryozoans are most likely to be found in marine environment, typically growing on surfaces of things, such as rocks, kelps, shells, fossils, and even on pipes and ships. Developed in colonies, some individuals gather up the food for the colony (autozooids), others depend on them (heterozooids). Some individuals devote to strengthen the colony (kenozooids) and vibracula clean the colony. These species have what's called "blind-ended" gut, pouch-like intestines where mouth and anus is same opening. Bryozoans do not have any defined respiratory, circulatory, and nerve system due to their size. Bryozoans have hydrostatic skeletal system.

Bryozoa is one of the few classical phyla from which no members have been found in the Cambrian. They seem to have evolved in the Ordovician.