Entoprocts

Phylum Entoprocta (Kamptozoa) Number of families 4

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Colonial or solitary tiny benthic animals with a tentacular crown on top, and a slender stalk that attaches basally to the substratum

Photo: Loxosomella sp. inhabiting parapodia of a polynoid polychaete found at Noto Peninsula, Japan. (Photo by Tohru Iseto. Reproduced by per-

Pedicellinidae

Evolution and systematics

There has been only one fossil record of Entoprocta, belonging to the extant genus Barentsia, which was collected from the Upper Jurassic of England. The phylogenetic relationships of Entoprocta to other invertebrate phyla are still obscure, but Entoprocta may have affinities to spiralians (animal groups that show spiral cleavage patterns). The phylum encompasses two orders, four families, sixteen genera, and approximately 170 species. The four families are: Barentsiidae, colonial species with a muscular swelling at the base of the stalk; Pedicellinidae, colonial species without basal muscular swelling, each zooid of a colony interrupted by stolon; Loxokalypodidae, colonial species without basal muscular swelling, component zooids of a colony erect from a common basal plate, not interrupted by stolons; and Loxosomatidae, which encompasses all solitary species.

The phylum name Entoprocta means "inside anus;" the phylum has this name because of its unique plan. The animal's anus opens inside its tentacular crown. Kamptozoa is another scientific name for this phylum; the name means "bending animal," and comes from the very active movement of these animals.

Physical characteristics

The calyx, or main body, of an entoproct contains a U-shaped gut, a ganglion, a pair of gonads, a pair of pro-tonephridia, and has a tentacular crown on top. Both the mouth and anus open inside the tentacular crown. The calyx is supported by a slender stalk that attaches basally to the substratum. In colonial species, zooids of a colony are generally connected by a highly branched stolon that creeps over the substratum. The solitary species have an attaching organ at the base of the stalk. In some species, however, the attaching organ degenerates in the adult stage and the adult animals are cemented onto the substratum.

Distribution

Entoprocts have been reported from tropical, temperate, and polar marine waters, and from shallow seashore to deep seas of more than 1,640 ft (500 m). One colonial species, Ur-natella gracilis, occurs worldwide in inland waters.

Habitat

Colonial species live on a wide variety of substrata, including rocks, stones, shell remains, human-made objects, and occasionally on other animals. Most solitary species have been known to live on the bodies of specific host animals, such as polychaetes, bryozoans, sponges, and sipunculans, and on the inner side of the tube of polychaetes.

Behavior

In response to irritation, entoprocts contract their tentacles and bend at the stalk. Some solitary species can glide over the substratum as slugs do. One solitary species (Loxosoma agile) somersaults across the substratum, and another species (Loxosomella bifida) can walk on the substratum similar to the way humans do, using a unique foot with two elongated, leglike extensions. Newly liberated buds of solitary species often swim using ciliary tentacles, contributing to the dispersal of the species.

Emily Damstra
Barentsia discreta bending. (Illustration by Emily Damstra) Urnatella gracilis bending. (Illustration by Emily Damstra)

Feeding ecology and diet

All entoprocts are suspension feeders, feeding on phyto-plankton or other organic particles in a water current they create using the cilia along their tentacles.

Reproductive biology

Each zooid of a colonial species is generally dioecious, male or female, but both sexes occur in a single colony. Solitary species are generally protandrous hermaphrodites, namely, animals are males in the early stage but later convert into females. Eggs are fertilized in the ovary and transferred to a brood pouch, a deep depression between the mouth and the anus, where embryos develop to trochophorelike larvae. Asexual reproduction (budding) is vigorous in all entoprocts. Buds occur from the tips of developing stolon, or from a basal disc and stalks in colonial species. In solitary species budding usually occurs at two latero-frontal areas of the calyx.

Conservation status

Entoprocts may be common in worldwide seas. However, their distribution and abundance are still poorly documented, and their responses to human activities have not been monitored. No species is listed by the IUCN.

Significance to humans

Entoprocts have no significance to humans.

Emily Damstra

1. Freshwater colonial entoproct (Urnatella gracilis)-, 2. Solitary entoproct (Loxomitra kefersteinii); 3. Marine colonial entoproct (Barentsia discreta). (Illustration by Emily Damstra)

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