Bryozoa, commonly known as moss animals are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies. Most marine bryozoans live in tropical waters, but a few are found in oceanic trenches and polar waters.

Typically about 0.5 millimetres (1/64 in) long, they have a special feeding structure called a lophophore, a "crown" of tentacles used for filter feeding. The bryozoans are classified as the marine bryozoans (Stenolaemata), freshwater bryozoans (Phylactolaemata), and mostly-marine bryozoans (Gymnolaemata), a few members of which prefer brackish water. 5,869 living species are known.[7] Originally all of the crown group Bryozoa were colonial, but as an adaptation to a mesopsammal (interstitial spaces in marine sand) life or to deep-sea habitats, secondarily solitary forms have since evolved. Solitary species has been described in four genera; Aethozooides, Aethozoon, Franzenella and Monobryozoon). The latter having a statocyst-like organ with a supposed excretory function.

The class Gymnolaemata includes the animals of the phylum Bryozoa, called Bryozoans, which are sesssile (lack of self-locomotion) and normally found on the surfaces of rocks and kelp. These animals are mostly marine and/or brackish water species and date back to the Paleozoic era.

Too, these bryozoans have a lophophore, which is feeding organ possessed by these species, all of which are aquatic organisms.

These animals are often found as a colonial organism in which they are referred to as a zooids.

Individual animals, called zooids, are cylindrical or flattened and grow in a colonial setting connected with other animals either directly by tissue or share a common exoskeleton. The colonial organism as a whole is called a zoon, (plural zoa), from the Greek zoion meaning animal..

The class Phylactolaemata includes the animals of the phylum Byrozoa, called Bryozoans. These animals are all freshwater species and like most all Bryozoans filter feed by means of an extensible crown called a lophophone.

Too, like most other Bryozoans, these animals live in colonies of zooids, each of which consists of clones of the founding member. Unlike marine bryozoans, phylactolaemate colonies consist of only one type of zooid, the feeding forms known as autozooids.

This class has only one extand Order.

The class Stenoaemata includes the animals of phylum Bryozoa, called bryozoans, which are exclusively marine species. These Stenolaemates date back to the Ordivician period of the Paleozoic era, and there are more than 600 extant species in the Order Cyclostomatida, which amounts to the third largest order of living bryozoans.

Like many other bryozoans, the species in this order are stationary filter feeder which live on the ocean floor, forming colonies with calcified exoskeletons.

Some species of the bryozoans grew as lacy or fan-like colonies which became important reef builders, and in some regions form an abundant component of limestones. There are about six extinct orders in the class Stenolaemates, which species were greatly reduced during the terminal Permian extinction event, and most all the remaining species were extinct by the start of the Jurassic.

A zooid is an individual bryozoan species, which live in colony and may be tubular, conical of sac-shaped. Each zooid may extend from the colony at an angle, and then extend its tentacles to filter feed.