Entoprocta - Feeding, Digestion, Excretion, Circulation and Respiration

Feeding, Digestion, Excretion, Circulation and Respiration

A band of cells, each with multiple cilia, runs along the sides of the tentacles, connecting each tentacle to its neighbors, except that there is a gap in the band nearest the anus. A separate band of cilia runs 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. The cilia on the sides of the tentacles create a current that flows into the "crown" at the bases of the tentacles and exits above the center of the "crown". These cilia pass food particles to the cilia on the inner surface of the tentacles, and the inner cillia produce a downward current that drives particles into and round the groove, and then to the mouth.

Entoprocts generally use one or both of: ciliary sieving, in which one band of cilia creates the feeding current and another traps food particles (the "seive"); and downstream collecting, in which food articles are trapped as they are about to exit past them. In entoprocts, downstream collecting is done by the same bands of cilia that generate the current; trochozoan larvae also use downstream collecting, but use a separate set of cilia to trap food particles.

In addition glands in the tentacles secrete sticky threads that capture large particles. 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. These unusual cells lie around the mouth, and may provide an additional means of capturing prey.

The stomach and intestine are lined with microvilli, which are thought to absorb nutrients. The anus, which opens inside the "crown", ejects solid wastes into the outgoing current after the tentacles have filtered food out of the water; in some families it is raised on a cone above the level of the groove that conducts food to the mouth. Most species have a pair of protonephridia which extract soluble wastes from the internal fluids and eliminate them through pores near the mouth. However the freshwater species Urnatella gracilis has multiple nephridia in the calyx and stalk.

The zooids absorb oxygen and emit carbon dioxide by diffusion, which works well for small animals.