Entoproctahairy back worms


Phylum Entoprocta (also known as Kamptozoa) includes nearly 200 currently known species of sessile, solitary (family Loxosomatidae) or colonial (families Loxokalypodidae, Pedicellinidae and Barentsiidae), primarily marine organisms, although two freshwater species, Loxosomatoides sirindhorne and Urnatella gracilis have been identified. Marine species are found throughout the world’s oceans, and Urnatella gracilis is found on all continents except Antarctica. These organisms superficially resemble cnidarian hydroids and bryozoans (Phylum Bryozoa); the main body consists of a cup-like calyx that bears a ring of ciliated tentacles, which is attached on its dorsal surface to the substrate (or stolon in colonial species) by a long, thin stalk. Whether solitary or colonial, all entoprocts are sessile suspension feeders. Entoprocts exhibit a range of reproductive modes and behaviors, including asexual clonal reproduction, as well as hermaphroditic and dioecious sexual reproduction. (Appeltans, et al., 2012; Brusca and Brusca, 2003; Nielsen, 2002; Ruppert, et al., 2004; Schwaha, et al., 2010; Zhang, 2011)

Geographic Range

The majority of entoprocts live in coastal, marine environments throughout the world. Urnatella gracilis is found in rivers on every continent except Antarctica, and Loxosomatoides sirindhorne has been identified from rivers in Thailand. (Brusca and Brusca, 2003; Ramel, 2012; Schwaha, et al., 2010; Wood, 2005)


Colonial entoprocts are found living on rocks, shells, algae, and underwater structures, preferring more solid substrates to softer sediments. Solitary species are found living on other animals such as sponges, sessile annelids, and ectoprocts, taking advantage of the feeding currents produced by these animals. They are found from intertidal areas to depths of up to 500 m. While marine species may be found in brackish environments, the two freshwater species are found only in fully freshwater environments. (Brusca and Brusca, 2003; Nielsen, 2002; Ruppert, et al., 2004; Weise, 1961; Wood, 2005)

Systematic and Taxonomic History

Following their discovery, these organisms were alternatively classified as special, polyp-like rotifers, or they were classified along with Bryozoa, in phylum Bryozoa. The name Entoprocta was first applied to these organisms by the German zoologist Hinrich Nitsche in 1870 to separate them from Bryozoa, based upon the position of the anus (inside the lophophore ring, rather than outside), embryonic cleavage pattern (spiral vs. radial), and differences in body cavity type (acoelomate vs. coelomate). These differences resulted in Hatschek elevating Entoprocta to phylum level in 1888. The name Kamptozoa would later be applied to this group by Carl Cori in 1929, and is still used interchangeably with Entoprocta. (Cori, 1929; Ellis, 1755; Hatschek, 1888; Nitsche, 1870; Pallas, 1774; Sars, 1835; van Beneden, 1845)

The monophyly of Entoprocta, as well as that of its two orders, Solitaria and Coloniales, is well supported by morphological characters and a recent molecular phylogenetic analysis. However, the evolutionary relationships of entoprocts to other phyla remain a matter of some debate. Recent molecular phylogenetic studies have suggested that entoprocts and ectoprocts should in fact be considered classes within a single taxon called Polyzoa, in agreement with their original classification. These, and additional molecular studies have suggested that Polyzoa should also include the obscure phylum Cycliophora, which appears to share a sister relationship with Entoprocta. These studies also suggest that Polyzoa be placed in a larger superphylum, Lophotrochozoa, based on the common presence of the trochophore larval state in member phyla (which include annelid worms, mollusks, flatworms, and nemertean worms, among others). There is no consensus, however, on which of the lophotrochozoan phyla represent the closest relative of modern polyzoans. (Fuchs, et al., 2010; Funch and Kristensen, 1995; Giribet, et al., 2004; Hausdorf, et al., 2007; Hejnol, et al., 2009; Helmkampf, et al., 2008; Paps, et al., 2009a; Paps, et al., 2009b)

  • Synonyms
    • Kamptozoa (Cori, 1929)
  • Synapomorphies
    • anus located inside ring of lophophore tentacles

Physical Description

These organisms superficially resemble cnidarian hydroids and bryozoans (phylum Bryozoa), with the main body consisting of a cup-like calyx that bears a ring of 6 to 36 ciliated tentacles, attached on its dorsal surface to the substrate (or stolon in colonial species) by a long, thin stalk. The calyx and stalk are covered by a thin, collagenous cuticle, which does not extend over the tentacles, and is underlaid by a cellular epidermis. Muscle bands beneath the epidermis allow the organism to compress its calyx and stalk, extend its tentacles, and bend its stalk. These organisms are functionally acoelomate, lacking a fluid-filled body cavity. It is uncertain whether this condition results from a secondary filling of an embryonic blastocoel with mesenchyme, or whether these organisms lack a blastocoel throughout development. The viscera are located entirely in the calyx, with the mouth and anus found on the ventral surface (vestibule), surrounded by the tentacular crown. The gut is U-shaped and lined with a layer of ciliated cells, widening into a stomach near the internal base of the calyx, followed by an intestinal segment that leads to the anus. Entoprocts are quite small, with individual zooids ranging from 0.1 to 7 mm in length. (Brusca and Brusca, 2003; Ramel, 2012; Ruppert, et al., 2004)

  • Sexual Dimorphism
  • sexes alike


Both colonial and solitary species are capable of asexual clonal reproduction by budding; species may reproduce sexually and be dioecious, simultaneous, or protandrous hermaphrodites. Eggs either hatch into planktonic larvae, or in some species, complete early development in a brood chamber (located in the atrium), attached by secretions of cement glands to the chamber's wall. In some brooding species, nutrition is provided to developing embryos via special placental cells; in others, the egg yolk nourishes the growing larvae. Planktonic larvae may remain free swimming for up to 7 months before settling, while those raised in a brood chamber will settle relatively quickly (within a few days of hatching). (Brusca and Brusca, 2003; Ruppert, et al., 2004; Shanks, 2001)

Entoproct embryonic development follows the holoblastic, spiral cleavage pattern typical of protostome organisms, with the mesoderm forming from the 4d mesentoblast. Development continues to a coeloblastula stage, after which, the embryos of most species proceed into a free swimming, feeding planktonic larval stage strongly resembling the trochophore larva of protostome species. Some species produce lecithotrophic or benthic crawling larvae. Trochophore larvae have equatorial ciliary bands (used for feeding on suspended particles), apical and ventral sensory tufts of cilia, pigment-cup ocelli that serve as light-sensing organs, a complete digestive system, and a pair of protonephridia for waste excretion. After their larval period, most entoprocts settle, attach to the substrate, and undergo metamorphosis. Unequal growth of the body directs the vestibular surface away from the substrate and the mouth, anus, and gut may rotate up to 180°, to face the vestibular surface; however, no rotation or unequal growth is necessary for some species. In these, an asexual bud forms from the attached larvae to form the zooid, which is already oriented in the correct position. (Brusca and Brusca, 2003; Nielsen, 2002)

Some species in family Loxosomatidae produce free swimming larvae that may produce adult buds precociously; the adults are held in a body pocket of the larvae until their release through the body wall, usually a few days. After release, the larvae die. In some species, adult buds have been noticed developing from larvae while the larvae were still developing in their parents' ovaries. In at least one species, males and females may be produced via budding. (Shanks, 2001)


Gonads, when present, are located just beneath the vestibular surface and empty into the water via the gonopore. Male zooids release sperm into the water, where it can be drawn into the reproductive tract of female zooids. Fertilization occurs in the ovaries or oviducts. (Brusca and Brusca, 2003)

Entoprocts exhibit a wide range of reproductive modes and behaviors. Both colonial and solitary species are capable of asexual clonal reproduction by budding. In colonial species, new zooids are formed from the stalk or the stolons joining individuals, while solitary species produce buds from the base of the calyx. Sexual reproduction also occurs and individuals may be dioecious, simultaneous, or protandrous hermaphrodites. Mating seasons depend on location; entoprocts from warmer waters may reproduce year-round, while many of those in more temperate waters show a breeding peak in late summer and early fall (experimental evidence supports increased water temperature as a trigger for sexual maturity). (Brusca and Brusca, 2003; Emschermann, 1985; Nielsen, 2002; Winston, 1982)

Beyond production of gametes and, in some cases, development of larvae in a brooding pouch (sometimes fed by placental cells), entoprocts do not display parental investment. (Brusca and Brusca, 2003; Ruppert, et al., 2004; Shanks, 2001)

  • Parental Investment
  • no parental involvement
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female


Although no definitive studies regarding the lifespan of entoprocts are currently available, feeding planktonic larvae of some species live for more than 7 months (at which point they settle and attach to the substrate). (Emschermann, 1985; Shanks, 2001)


Entoprocts may be colonial or solitary. An entoproct may shed (typically under adverse environmental conditions) and regenerate its calyx, sometimes changing sex when it does; most entoprocts with this ability are colonial (only one species of solitary entoproct, Loxosomella antarctia is noted to regenerate the entire calyx in this way). It is possible to fold the tentacles and move the calyx using subepidermal musculature of the body and stalk. Once larvae have settled, they are most typically sessile, using a "foot" to attach to a substrate. A few species are reportedly capable of movement even after adulthood, for instance members of genus Loxasomella inside the tubes of marine annelids. (Brusca and Brusca, 2003; Emschermann, 1993; Margulis, et al., 1999; Ramel, 2012)

Communication and Perception

Entoprocts have greatly reduced nervous systems, consisting of a single subenteric ganglion between the vestibular surface and stomach. This enervates the tentacles, calyx, and stalk via several pairs of nerves arising from the central ganglionic mass. Tactile receptors are scattered over the body and concentrated on the tentacles. Some species in family Loxosomatidae have ciliated papillae, which form lateral sense organs as well. (Brusca and Brusca, 2003; Ruppert, et al., 2004)

Food Habits

All entoprocts are sessile suspension feeders. The cilia on their tentacles generate water currents that carry small food particles (particularly phytoplankton, as well as diatoms and algae) to a ciliated food groove at the base of the tentacular crown. The tentacles also have glandular cells that secrete a sticky substance to capture larger food particles, which are also moved to the food groove. The cilia in the food groove carry food to the mouth, where a combination of ciliary action and muscle contractions move the food through the digestive system. One species of entoproct, Loxocorone brochobola, has nematocyst-type organs; their function is unknown but may be related to feeding. (Brusca and Brusca, 2003; Emschermann, 1993; Weise, 1961)


As very small invertebrates, entoprocts are likely prey to many larger marine and freshwater animals. Known predators include small crustaceans and mollusks, flatworms, and nudibranchs. (Canning and Carlton, 2000; Ramel, 2012; Wood, et al., 2006)

Ecosystem Roles

Solitary entoprocts are most often commensal on invertebrates such as sponges, annelids, sipunculans, ascidians, and ectoprocts. There is a high level of host specificity. Entoproct colonies may also be found on mollusk shells. There are no parasitic forms currently recognized and there is no data currently available regarding parasites of these animals. (Bleidorn, 2008; Brusca and Brusca, 2003; Emschermann, 1993; Kristensen, 1970; Weise, 1961; Wood, 2005)

A phoretic relationship has been identified between Urnatella gracilis and larval Cordalus cornutus (commonly called hellgrammites, the larval form of Eastern dobsonflies); as a result of this relationship, entoprocts gain a means of dispersal, protection from predators, and nutrition. (Tracy and Hazelwood, 1983)

Species Used as Host
Mutualist Species
  • eastern dobsonflies (Cordalus cornutus)

Economic Importance for Humans: Positive

Beyond the potential for scientific research, there are no known positive effects of entoproct species on humans. (Brusca and Brusca, 2003)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

Entoprocts may be a cause of water and vessel fouling. (Canning and Carlton, 2000; Soule and Soule, 1968)

Conservation Status

There is currently no concern regarding entoproct species becoming threatened or endangered. (Brusca and Brusca, 2003)

  • IUCN Red List [Link]
    Not Evaluated

Other Comments

While rare, entoproct fossils date back to approximately 520 million years ago, during the Cambrian period. (Zhang, et al., 2013)


Jeremy Wright (author), University of Michigan-Ann Arbor, Leila Siciliano Martina (editor), Animal Diversity Web Staff.



Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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living in the southern part of the New World. In other words, Central and South America.

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living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.


the nearshore aquatic habitats near a coast, or shoreline.


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.


having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.


active at dawn and dusk

  1. active during the day, 2. lasting for one day.

union of egg and spermatozoan


mainly lives in water that is not salty.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.

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Found in northern North America and northern Europe or Asia.

internal fertilization

fertilization takes place within the female's body

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


found in the oriental region of the world. In other words, India and southeast Asia.

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reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an animal that mainly eats plankton


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.


condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products


structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


remains in the same area


non-motile; permanently attached at the base.

Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa


reproduction that includes combining the genetic contribution of two individuals, a male and a female


lives alone


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

year-round breeding

breeding takes place throughout the year


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