Entoprocts range in height from 0.5 - 5 mm, and 150 species have been described; all are aquatic and mostly marine. It is thought that they are sequentially hermaphrodite, and that fertilisation may be internal. It is speculated by some authorities that they may be related to the Bryozoans, and that they are not truly pseudocoelomate. Superficially they resemble the hydroid form of Cnidarians. There are both solitary and colonial species. On the right is Lexosomella sp. a solitary species. The marine species grow on shells and algae, and commensal with polychaete annelids. The few freshwater species (see Urnatella gracilis on the left) are found on the undersides of rocks in running water.

The body is an oval structure containing the internal organs and an attachment disc or stalk with adhesive glands. They are filter-feeders with cilia on the tentacles which keep water moving in a steady current, capturing food particles and moving them down to the mouth. The body surface has sensory bristles and pits. Gaseous exchange occurs over the body surface.