Diversity
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
Ectoprocta
); 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.
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.
- Biogeographic Regions
- nearctic
- palearctic
- oriental
- ethiopian
- neotropical
- australian
- Other Geographic Terms
- holarctic
- cosmopolitan
Habitat
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.
- Habitat Regions
- temperate
- tropical
- saltwater or marine
- freshwater
- Aquatic Biomes
- benthic
- reef
- rivers and streams
- coastal
- brackish water
- Other Habitat Features
- intertidal or littoral
Systematic and Taxonomic History
Following their discovery, these organisms were alternatively classified as special,
polyp-like rotifers, or they were classified along with
Ectoprocta
, in phylum
Bryozoa
. The name
Entoprocta
was first applied to these organisms by the German zoologist Hinrich Nitsche in 1870
to separate them from
Ectoprocta
, 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
.
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.
Physical Description
These organisms superficially resemble cnidarian hydroids and bryozoans (phylum
Ectoprocta
), 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.
- Other Physical Features
- heterothermic
- bilateral symmetry
- Sexual Dimorphism
- sexes alike
Development
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).
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.
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.
- Development - Life Cycle
- metamorphosis
Reproduction
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.
- Mating System
- polygynandrous (promiscuous)
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).
- Key Reproductive Features
- seasonal breeding
- year-round breeding
- gonochoric/gonochoristic/dioecious (sexes separate)
- simultaneous hermaphrodite
- sequential hermaphrodite
- sexual
- asexual
- fertilization
- oviparous
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.
- Parental Investment
- no parental involvement
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
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).
Behavior
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.
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.
- Communication Channels
- tactile
- Perception Channels
- tactile
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,
Loxosomella brochobola
, has nematocyst-type organs; their function is unknown but may be related to feeding.
- Primary Diet
- planktivore
Predation
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
.
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.
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.
- Clymenella zonalis (Class Polychaeta , Phylum Annelida )
- Nephtyidae sp. (Class Polychaeta , Phylum Annelida )
- Polynoidae sp. (Class Polychaeta , Phylum Annelida )
- Amblema sp. (Class Bivalvia , Phylum Mollusca )
- Dreissena polymorpha (Class Bivalvia , Phylum Mollusca )
- Pleurocera caniculatum (Class Gastropoda , Phylum Mollusca )
- Ophioplinthus gelida (Class Ophiuroidea , Phylum Echinodermata )
- Phascolion strombi (Class Sipunculidea , Phylum Sipuncula )
- 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.
- Positive Impacts
- research and education
Economic Importance for Humans: Negative
Entoprocts
may be a cause of water and vessel fouling.
Conservation Status
There is currently no concern regarding
entoproct
species becoming threatened or endangered.
Other Comments
While rare,
entoproct
fossils date back to approximately 520 million years ago, during the Cambrian period.
Additional Links
Contributors
Jeremy Wright (author), University of Michigan-Ann Arbor, Leila Siciliano Martina (editor), Texas State University.
- Nearctic
-
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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- oriental
-
found in the oriental region of the world. In other words, India and southeast Asia.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Neotropical
-
living in the southern part of the New World. In other words, Central and South America.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Australian
-
Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- holarctic
-
a distribution that more or less circles the Arctic, so occurring in both the Nearctic and Palearctic biogeographic regions.
Found in northern North America and northern Europe or Asia.
- cosmopolitan
-
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.
- temperate
-
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).
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- freshwater
-
mainly lives in water that is not salty.
- benthic
-
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.
- reef
-
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.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- brackish water
-
areas with salty water, usually in coastal marshes and estuaries.
- intertidal or littoral
-
the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.
- heterothermic
-
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.
- 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.
- metamorphosis
-
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.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- seasonal breeding
-
breeding is confined to a particular season
- year-round breeding
-
breeding takes place throughout the year
- protandrous
-
condition of hermaphroditic animals (and plants) in which the male organs and their products appear before the female organs and their products
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- asexual
-
reproduction that is not sexual; that is, reproduction that does not include recombining the genotypes of two parents
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female's body
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- crepuscular
-
active at dawn and dusk
- sessile
-
non-motile; permanently attached at the base.
Attached to substratum and moving little or not at all. Synapomorphy of the Anthozoa
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- solitary
-
lives alone
- colonial
-
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.
- tactile
-
uses touch to communicate
- tactile
-
uses touch to communicate
- planktivore
-
an animal that mainly eats plankton
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