Entoprocta

(Entoprocts)

Phylum Entoprocta (Kamptozoa)

Number of families 4

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

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 protonephridia, 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, Urnatella 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.

Feeding ecology and diet

All entoprocts are suspension feeders, feeding on phytoplankton 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.

Species accounts

List of Species

Marine colonial entoproct

Barentsia discreta

order

Coloniales

family

Barentsiidae

taxonomy

Ascopodaria discreta Busk, 1886, Nightingale Island, Tristan de Cunha.

other common names

None known.

physical characteristics

Total length of each zooid up to 0.4 in (9.5 mm), usually 0.1–0.2 in (3–6 mm). Tentacles number about 20. Stalk is thin and long, about three to eight times longer than calyx, with many tiny pores, and a muscular swelling at base of stalk. Each zooid of a colony is interconnected by a stolon.

distribution

Cosmopolitan, but not in northern Europe. Ranges from shallow coastal zone to deep seas of more than 1,640 ft (500 m).

habitat

On any nonliving substrata, including rocks, stones, and dock pilings, as well as on living substrata, such as worm tubes.

behavior

In response to a disturbance, it bends from basal muscular swelling, but the stalk itself does not curve. Action of one individual leads actions of surrounding zooids.

feeding ecology and diet

Suspension feeder. Feeds on phytoplankton and organic particles.

reproductive biology

Buds at tips of developing stolon. Single colony contains both male and female zooids. Embryos brooded at brood pouch. Larva trochophorelike.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Freshwater colonial entoproct

Urnatella gracilis

order

Coloniales

family

Barentsiidae

taxonomy

Urnatella gracilis Leidy, 1951, Schuylkill River, Pennsylvania, United States.

other common names

None known.

physical characteristics

Height of the colony is 0.08–0.12 in (2–3 mm), and each zooid has 12–16 tentacles. In addition to a basal muscular swelling common to Barentsiidae species, numerous muscular swellings are present throughout the stalk. One or two original stalks erect from a basal plate, successive stalks branch from older stalks. Calyx at tip of each branch of stalk. No interrupting stolons.

distribution

Belgium, Germany, Hungary, Romania, Russia (Don River), India, Japan, Africa (Nile River, Congo River, and Lake Tanganyika), United States, South America (Parana and Uruguay Rivers).

habitat

In freshwater on stones, twigs, and remains of shells.

behavior

In response to a disturbance, it bends from muscular swellings of the stalks. Fragments of colony with two to three young zooids detach from the colony, drift in water current, or creep on substratum. Eventually, they fix on a favorable habitat and generate a new colony.

feeding ecology and diet

Suspension feeder. Feeds on phytoplankton and organic particles.

reproductive biology

Buds at basal plate and stalks. Larva trochophorelike. Sexual reproduction is very rare. Calyx often degenerates in low temperature or in any insufficient condition, but regenerates in favorable conditions.

conservation status

Originally found in the United States. Current worldwide distribution may be due to human activities but the transfer mechanism is still unknown. Not listed by the IUCN.

significance to humans

None known.

Solitary entoproct

Loxomitra kefersteinii

order

Solitaria

family

Loxosomatidae

taxonomy

Loxosoma kefersteinii Claparède, 1867, Naples, Italy.

other common names

None known.

physical characteristics

Total length up to 0.06 in (1.5 mm). Tentacles number 10–14. Stalk slender, about three times longer than calyx. Bud has tiny attaching organ at base of stalk, but adult loses it and fixes onto substratum.

distribution

South Wales, Great Britain; Naples, Italy; Red Sea; Florida, United States.

habitat

Solitary species. Lives on substrata such as body surface of other animals, settlement panels, and water pipes.

behavior

In response to a disturbance, it bends along slender, flexible stalk. Newly liberated bud lays its body horizontally and crawls on substratum, twisting the whole body in search of a favorable point to attach to.

feeding ecology and diet

Suspension feeder. Feeds on phytoplankton and organic particles.

reproductive biology

Budding occurs at latero-frontal areas of calyx. Up to 12 buds on a single animal. Sexual reproduction has not been observed.

conservation status

Not listed by the IUCN.

significance to humans

None known.

Resources

Books

Hyman, L. H. The Invertebrates: Acanthocephala, Aschelminthes, and Entoprocta. Vol. 3, The Pseudocoelomate Bilateria. New York: McGraw-Hill, 1951.

Nielsen, C. "Entoprocts." In Synopses of the British Fauna (New Series) 41, edited by Doris M. Kermack and R. S. K. Barnes. Leiden, The Netherlands: E. J. Brill., 1989.

Periodicals

Wasson, K. "A Review of the Invertebrate Phylum Kamptozoa (Entoprocta) and Synopses of Kamptozoan Diversity in Australia and New Zealand." Transactions of the Royal Society of South Australia 126 (2002): 1–20.

Tohru Iseto, PhD