[4] Entoprocts are superficially like bryozoans (ectoprocts), as both groups have a "crown" of tentacles whose cilia generate water currents that draw food particles towards the mouth.

[4] The body of a mature entoproct zooid has a goblet-like structure with a calyx mounted on a relatively long stalk that attaches to a surface.

The mouth and anus lie on opposite sides of the atrium (space enclosed by the "crown" of tentacles), and both can be closed by sphincter muscles.

[4] The stalks of colonial species arise from shared attachment plates or from a network of stolons, tubes that run across a surface.

The epidermis contains only a single layer of cells, each of which bears multiple cilia ("hairs") and microvilli (tiny "pleats") that penetrate through the cuticle.

A separate band of cilia grows along a groove that runs close to the inner side of the base of the "crown", with a narrow extension up the inner surface of each tentacle.

[4] A non-colonial species reported from around the Antarctic Peninsula in 1993 has cells that superficially resemble the cnidocytes of cnidaria, and fire sticky threads.

[18] In some species of the genera Loxosomella and Loxosoma, the larva produces one or two buds that separate and form new individuals, while the trochophore disintegrates.

Larvae of most species undergo a complex metamorphosis, and the internal organs may rotate by up to 180°, so that the mouth and anus both point upwards.

[7] The phylum consists of about 150 recognized species, grouped into 4 families:[4][6] Since entoprocts are small and soft-bodied, fossils have been extremely rare.

[24] In 1977, Simon Conway Morris provided the first description of Dinomischus, a sessile animal with calyx, stalk and holdfast, found in Canada's Burgess Shale, which was formed about 505 million years ago.

These resemble the modern colonial genus Barentsia in many ways, including: upright zooids linked by a network of stolons encrusting the surface to which the colony is attached; straight stalks joined to the stolons by bulky sockets with transverse bands of wrinkles; overall size and proportions similar to that of modern species of Barentsia.

[25] When entoprocts were discovered in the nineteenth century, they and bryozoans (ectoprocts) were regarded as classes within the phylum Bryozoa, because both groups were sessile animals that filter-fed by means of a "crown" of tentacles that bore cilia.

[27] However, studies by one team in 2007 and 2008 argue for sinking Entoprocta into Bryozoa as a class, and resurrecting Ectoprocta as a name for the currently identified bryozoans.

[26][28] The consensus of studies from 1996 onwards has been that entoprocts are part of the Trochozoa, a protostome "superphylum" whose members are united in having as their most basic larval form the trochophore type.

[4] While the great majority are marine, two species live in freshwater: Loxosomatoides sirindhornae, reported in 2004 in central Thailand, and Urnatella gracilis, found in all the continents except Antarctica.

[4] The solitary species, which are marine,[3] live on other animals that feed by producing water currents, such as sponges, ectoprocts and sessile annelids.

[31] Small colonies of the freshwater entoproct Urnatella gracilis have been found living on the aquatic larvae of the dobsonfly Corydalus cornutus.

The ectoprocts gain a means of dispersal, protection from predators and possibly a source of water that is rich in oxygen and nutrients, as colonies often live next to the gills of the larval flies.

Hence it is difficult to determine whether a specimen belongs to a species that already occurs in the same area or is an invader, possibly as a result of human activities.