Endoprocta

The phylum Endoprocta is a group of about 60 species that closely resemble moss animals or members of the phylum Bryozoa. With the exception of the genus Urnatella all endoprocts are marine-dwelling species. Like moss animals they are sessile, being attached to a wide range of submerged objects such as rocks, shells, sponges, corals, and other objects. These tiny animals—the largest measures just 0.2 in (5 mm) in length—may either live a solitary or colonial existence. All members of the phylum are filter feeders that extract plankton and other food particles from the water column.

Body form varies considerably in this phylum, with most species being an oval shape. Solitary species are usually positioned on a short stalk while colonial species may have a large number of individual animals all arising from a single, spreading stalk. The top of the animal is dominated by a ring of short tentacles which are produced directly from the body wall and which may be withdrawn when the animal is not feeding. The mouth is at the center of this ring, the anus at the opposite pole. As with other small, filter-feeding organisms, a mass of tiny cilia line the inner side of the tentacles. When they beat, they create a downward current drawing water and food particles towards the animal, in between the tentacles and towards the mouth. From here, additional cilia continue the downward movement of food items towards the stomach.

Asexual reproduction is common in both solitary and colonial species. Many endoprocts also produce male and female gametes. Fertilization is thought to be internal although the exact process underlying this is not known. Fertilized eggs develop into free-living and free-swimming larvae known as a trocophore, which, after a short period at sea, settles and attaches itself firmly to some substrate.