Editing Entoprocta

{{Short description|Phylum of aquatic invertebrates}}
{{good article}}
{{Automatic taxobox
| fossil_range = {{Fossil range | Early Cambrian|Recent}}<ref name=Zhang>{{cite journal|last1=Zhang|first1=Zhifei|title=A sclerite-bearing stem group entoproct from the early Cambrian and its implications|journal=Scientific Reports|date=January 2013|volume=3|doi=10.1038/srep01066 |doi-access=free |last2=Holmer |first2=Lars E. |last3=Skovsted |first3=Christian B. |last4=Brock |first4=Glenn A. |last5=Budd |first5=Graham E. |last6=Fu |first6=Dongjing |last7=Zhang |first7=Xingliang |last8=Shu |first8=Degan |last9=Han |first9=Jian |last10=Liu |first10=Jianni |last11=Wang |first11=Haizhou |last12=Butler |first12=Aodhán |last13=Li |first13=Guoxiang |page=1066|display-authors=1 |pmid=23336066 |pmc=3548229|bibcode=2013NatSR...3E1066Z}}</ref><ref name="Todd1992">{{Cite journal | last1 = Todd | first1 = J. A. | last2 = Taylor | first2 = P. D. | doi = 10.1007/BF01138708 | title = The first fossil entoproct | journal = Naturwissenschaften | volume = 79 | issue = 7 | pages = 311–314 | year = 1992 | bibcode = 1992NW.....79..311T | s2cid = 44229586 }}</ref>
| display_parents = 8
| taxon = Entoprocta
| authority = [[Hinrich Nitsche|Nitsche]], 1870
| image = Barentsia_ramosa_171739034.jpg
| image_caption = ''Barentsia ramosa''
| synonyms =
* [[#Names|Kamptozoa]]
| subdivision_ranks = Families
| subdivision =
*[[Barentsiidae]] (= Urnatellidae){{citation needed|date=December 2024|reason=ITIS says Urnatellidae Annandale, 1915 (https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156752#null) is a junior synonym of Pedicellinidae  Johnston, 1847, but places ''Urnatella'' Leidy, 1851 (https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156753#null) in Barentsiidae Emschermann, 1972}} 
*[[Loxokalypodidae]]
*[[Loxosomatidae]]
*[[Pedicellinidae]]
*''[[incertae sedis]]''
**†''[[Cotyledion]]''
}}

'''Entoprocta''' {{IPAc-en|E|n|t|ou|'|p|r|Q|k|t|@}} ({{lit|inside rectum/anus}}), or '''Kamptozoa''' {{IPAc-en|k|ae|m|(|p|)|t|@|'|z|ou|@}}, is a [[phylum (biology)|phylum]] of mostly [[Sessility (zoology)|sessile]] aquatic [[animal]]s, ranging from {{convert|0.1|to|7|mm|in|sigfig=1}} long. Mature individuals are [[goblet]]-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that [[filter feeder|draw food particles]] towards the mouth, and both the mouth and anus lie inside the "crown". The superficially similar [[Bryozoa]] (Ectoprocta) have the anus outside a "crown" of hollow tentacles. Most [[family (biology)|families]] of entoprocts are colonial, and all but 2 of the 150&nbsp;species are marine. A few solitary species can move slowly.

Some species eject unfertilized [[ovum|ova]] into the water, while others keep their ova in brood chambers until they hatch, and some of these species use [[placenta]]-like organs to nourish the developing eggs. After hatching, the [[larva]]e swim for a short time and then settle on a surface. There they [[Metamorphosis|metamorphose]], and the larval gut rotates by up to 180°, so that the mouth and anus face upwards. Both colonial and solitary species also reproduce by [[cloning]] — solitary species grow clones in the space between the tentacles and then release them when developed, while colonial ones produce new members from the stalks or from corridor-like [[stolon]]s.

Fossils of entoprocts are very rare, and the earliest specimens that have been identified with confidence date from the Late [[Jurassic]]. Most studies from 1996 onwards have regarded entoprocts as members of the [[Trochozoa]], which also includes [[mollusc]]s and [[annelid]]s. However, a study in 2008 concluded that entoprocts are closely related to bryozoans. Other studies place them in a clade [[Tetraneuralia]], together with molluscs.

==Names==
"Entoprocta", coined in 1870,<ref name="Wood2005LoxosomatoidesSirindhornae">{{cite journal|last=Wood|first=T.S.|year=2005|title=''Loxosomatoides sirindhornae'', new species, a freshwater kamptozoan from Thailand (Entoprocta)|journal=Hydrobiologia|volume=544|pages=27–31|doi=10.1007/s10750-004-7909-x|s2cid=23481992}}</ref> means "[[anus]] inside".<ref name="RuppertFoxBarnesKamptozoa">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp| title=Invertebrate Zoology | chapter=Kamptozoa and Cycliophora | publisher=Brooks/Cole | edition=7th | isbn=0-03-025982-7 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/808 808–812] | url=https://archive.org/details/isbn_9780030259821/page/808 }}</ref> The alternative name "Kamptozoa", meaning "bent" or "curved" animals,<ref>The prefix "campto-" is explained at:
*{{cite book|last=Gledhill|first=D.|title=The names of plants|publisher=Cambridge University Press|year=2008|pages=88|isbn=978-0-521-86645-3|url=https://books.google.com/books?id=NJ6PyhVuecwC&q=campto-+kampto-|access-date=10 Sep 2009}}
*{{cite journal|last=Oestreich|first=A.E.|author2=Kahane, H. |author3=Kahane, R. |title=Camptomelic dysplasia|journal=Pediatric Radiology|volume=13|issue=4|pages=246–247|doi=10.1007/BF00973171|year=1983|pmid=6888999|s2cid=28821842}}</ref> was assigned in 1929.<ref name="Wood2005LoxosomatoidesSirindhornae" /> Some authors use "Entoprocta",<ref name="ITISEntoprocta">{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156732|title=ITIS Standard Report Page: Entoprocta|year=2006|publisher=Integrated Taxonomic Information System|access-date=2009-08-26}}</ref><ref name="Nielsen2001InEncOfLifeSciEntoprocta" /> while others prefer "Kamptozoa".<ref name="RuppertFoxBarnesKamptozoa" /><ref name="Wasson1997SystematicRevision" />

==Description==
Most species are colonial, and their members are known as "zooids",<ref name="RuppertFoxBarnesKamptozoa829">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp| title=Invertebrate Zoology | chapter=Lophoporata | publisher=Brooks / Cole | edition=7th | isbn=0-03-025982-7 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/829 829–845] | url=https://archive.org/details/isbn_9780030259821/page/829 }}</ref> since they are not fully independent animals.<ref>{{cite book|last=Little|first=W.|author2=Fowler, H.W.|author3=Coulson, J.|author4=Onions, C.T.|name-list-style=amp|title=Shorter Oxford English Dictionary|publisher=Oxford University Press|year=1964|chapter=Zooid|isbn=0-19-860613-3}}</ref> [[Zooid]]s are typically {{convert|1|mm|in}} long but range from {{convert|0.1|to|7|mm|in|sigfig=1}} long.<ref name="RuppertFoxBarnesKamptozoa" />

===Distinguishing features===
Entoprocts are superficially like [[bryozoa]]ns (ectoprocts), as both groups have a "crown" of tentacles whose [[cilia]] generate water currents that draw food particles towards the mouth. However, they have different feeding mechanisms and internal anatomy, and bryozoans undergo a [[metamorphosis]] from [[larva]] to adult that destroys most of the larval tissues; their colonies also have a founder zooid which is different from its "daughters".<ref name="RuppertFoxBarnesKamptozoa" />

{| class="wikitable" style="margin: 1em auto 1em auto" <!-- align="center" does not work -->
|+ Summary of distinguishing features
|- align="center"
! &nbsp; !! Entoprocta<ref name="RuppertFoxBarnesKamptozoa" /> !! Bryozoa (Ectoprocta)<ref name="RuppertFoxBarnesKamptozoa"/>
|- align="center"
! Tentacles
| Solid || Hollow
|- align="center"
! Feeding current
| From bases to tips of tentacles || From tips to bases of tentacles
|- align="center"
! Position of [[anus]]
| Inside "crown" of tentacles || Outside "crown" of tentacles
|- align="center"
! [[Coelom]]
| none || Three-part
|- align="center"
! Shape of founder zooid in a colony
| Same as other zooids || Round, unlike normal zooids<ref name="RichFenton1997Bryozoans">{{cite book|last=Rich|first=T.H.|author2=Fenton, M.A. |author3=Fenton, C.L. |title=The fossil book|publisher=Dover Publications|year=1997|pages=142–152|chapter="Moss Animals", or Bryozoans|isbn=978-0-486-29371-4|chapter-url=https://books.google.com/books?id=_ntSspji0LYC&q=bryozoans&pg=PA141|access-date=2009-08-07}}</ref>
|- align="center"
! Metamorphosis to adult
| Retains most larval structures || Destroys most larval structures
|- align="center"
! Excretory organs
| [[Protonephridia]] || None
|}
{{clear}}

===Zooids===
[[File:Barentsia laxa 1498941.png|thumb|280px|''Barentsia laxa'']]
The body of a mature entoproct zooid has a goblet-like structure with a [[Calyx (zoology)|calyx]] mounted on a relatively long stalk that attaches to a surface. The rim of the calyx bears a "crown" of 8 to 30&nbsp;solid tentacles, which are extensions of the body wall. The base of the "crown" of tentacles is surrounded by a membrane that partially covers the tentacles when they retract. The mouth and anus lie on opposite sides of the atrium (space enclosed by the "crown" of tentacles), and both can be closed by [[sphincter]] muscles. The gut is U-shaped, curving down towards the base of the calyx, where it broadens to form the stomach. This is lined with a membrane consisting of a single layer of cells, each of which has multiple [[cilia]].<ref name="RuppertFoxBarnesKamptozoa" />
[[File:Pedicellina cernua 001.png|thumb|left|''Pedicellina cernua'' (magnified x&nbsp;27)]]
The stalks of colonial species arise from shared attachment plates or from a network of [[stolon]]s, tubes that run across a surface.<ref name="RuppertFoxBarnesKamptozoa" /> In solitary species, the stalk ends in a muscular sucker, or a flexible foot, or is cemented to a surface.<ref name="Nielsen2001InEncOfLifeSciEntoprocta">{{Cite book
| chapter=Entoprocta | author=Nielsen, C.
| title=Encyclopedia of Life Sciences | year=2002 | publisher= John Wiley & Sons, Ltd. | doi=10.1038/npg.els.0001596
| isbn=0-470-01617-5
}}</ref> The stalk is muscular and produces a characteristic nodding motion. In some species it is [[Segmentation (biology)|segmented]]. Some solitary species can move, either by creeping on the muscular foot or by [[somersault]]ing.<ref name="RuppertFoxBarnesKamptozoa" />

The body wall consists of the [[Epidermis (zoology)|epidermis]] and an external [[cuticle]],<ref name="RuppertFoxBarnesKamptozoa" /> which consists mainly of criss-cross [[collagen]] fibers. The epidermis contains only a single layer of cells, each of which bears multiple cilia ("hairs") and [[microvilli]] (tiny "pleats") that penetrate through the cuticle.<ref name="RuppertFoxBarnesKamptozoa" /> The stolons and stalks of colonial species have thicker cuticles, stiffened with [[chitin]].<ref name="Nielsen2001InEncOfLifeSciEntoprocta" />

There is no [[coelom]] (internal fluid-filled cavity lined with [[peritoneum]]) and the other internal organs are embedded in [[connective tissue]] that lies between the stomach and the base of the "crown" of tentacles. The [[nervous system]] runs through the connective tissue and just below the epidermis, and is controlled by a pair of [[ganglia]]. Nerves run from these to the calyx, tentacles and stalk, and to sense organs in all these areas.<ref name="RuppertFoxBarnesKamptozoa" />

==Vegetative functions==
A band of cells, each with multiple cilia, runs along the sides of the tentacles, connecting each tentacle to its neighbors, except that there is a gap in the band nearest the anus. A separate band of cilia grows along a groove that runs close to the inner side of the base of the "crown", with a narrow extension up the inner surface of each tentacle.<ref name="Nielsen2001InEncOfLifeSciEntoprocta" /> The cilia on the sides of the tentacles create a current that flows into the "crown" at the bases of the tentacles and exits above the center of the "crown".<ref name="RuppertFoxBarnesKamptozoa" /> These cilia pass food particles to the cilia on the inner surface of the tentacles, and the inner cilia produce a downward current that drives particles into and around the groove, and then to the mouth.<ref name="Nielsen2001InEncOfLifeSciEntoprocta" />

Entoprocts generally use one or both of: ciliary sieving, in which one band of cilia creates the feeding current and another traps food particles (the "[[sieve]]"); and downstream collecting, in which food particles are trapped as they are about to exit past them. In entoprocts, downstream collecting is carried out by the same bands of cilia that generate the current; [[trochozoan]] larvae also use downstream collecting, but use a separate set of cilia to trap food particles.<ref>{{cite journal|doi=10.3354/meps207033|last=Riisgård|first=H.U.|author2=Nielsen, C. |author3=Larsen, P.S. |year=2000|title=Downstream collecting in ciliary suspension feeders: the catch-up principle|journal=Marine Ecology Progress Series|volume=207|pages=33–51|bibcode=2000MEPS..207...33R|url=https://www.int-res.com/articles/meps/207/m207p033.pdf|access-date=12 Sep 2009|doi-access=free}}</ref>

In addition, glands in the tentacles secrete sticky threads that capture large particles.<ref name="RuppertFoxBarnesKamptozoa" /> A non-colonial species reported from around the [[Antarctic Peninsula]] in 1993 has cells that superficially resemble the [[cnidocyte]]s of [[cnidaria]], and fire sticky threads. These unusual cells lie around the mouth, and may provide an additional means of capturing prey.<ref>{{cite journal|last=Emschermann|first=P.|date=April 1993|title=On Antarctic Entoprocta|journal=Biological Bulletin|volume=184|pages=153–185|url=http://www.biolbull.org/cgi/reprint/184/2/153.pdf|access-date=12 Sep 2009|issue=2|doi=10.2307/1542225|jstor=1542225|pmid=29300524}}</ref>

The stomach and intestine are lined with [[microvilli]], which are thought to absorb nutrients. The anus, which opens inside the "crown", ejects solid wastes into the outgoing current after the tentacles have filtered food out of the water; in some [[family (biology)|families]] it is raised on a cone above the level of the groove that conducts food to the mouth.<ref name="RuppertFoxBarnesKamptozoa" /><ref>{{cite book | author=Barnes, R.S.K.| title=The invertebrates: a synthesis | chapter=The Lophophorates | pages=142–143 | edition=3rd | year=2001 | publisher=Wiley-Blackwell | isbn=0-632-04761-5 }}</ref> Most species have a pair of [[protonephridia]] which extract soluble wastes from the internal fluids and eliminate them through pores near the mouth. However, the freshwater species ''[[Urnatella gracilis]]'' has multiple nephridia in the calyx and stalk.<ref name="RuppertFoxBarnesKamptozoa" />

The zooids absorb [[oxygen]] and emit [[carbon dioxide]] by [[diffusion]],<ref name="RuppertFoxBarnesKamptozoa" /> which works well for small animals.<ref>{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp| title=Invertebrate Zoology | chapter=Introduction to Metazoa | publisher=Brooks / Cole | edition=7th | isbn=0-03-025982-7 | year=2004 | page=[https://archive.org/details/isbn_9780030259821/page/65 65] | url=https://archive.org/details/isbn_9780030259821/page/65 }}</ref>

==Reproduction and life cycle==
{{Annotated image/Trochophore larva}}Most species are simultaneous [[hermaphrodite]]s, but some switch from male to female as they mature, while individuals of some species remain of the same sex all their lives. Individuals have one or two pairs of [[gonad]]s, placed between the atrium and stomach, and opening into a single [[gonopore]] in the atrium.<ref name="Nielsen2001InEncOfLifeSciEntoprocta" /> The eggs are thought to be fertilized in the [[ovary|ovaries]]. Most species release eggs that hatch into [[planktonic]] [[larva]]e, but a few brood their eggs in the gonopore. Those that brood small eggs nourish them by a [[placenta]]-like organ, while larvae of species with larger eggs live on stored [[yolk]].<ref name="RuppertFoxBarnesKamptozoa" /> The development of the fertilized egg into a larva follows a typical [[spiralian]] pattern: the cells divide by [[Cleavage (embryo)#Holoblastic|spiral cleavage]], and [[mesoderm]] develops from a specific [[cell (biology)|cell]] labelled "4d" in the early [[embryo]].<ref>{{cite journal|last=Lambert|first= J.D.|year=2008|title=Mesoderm in spiralians: the organizer and the 4d cell|journal=Journal of Experimental Zoology|publisher=Wiley InterScience|volume=310B|pages=15–23|doi=10.1002/jez.b.21176 |pmid=17577229|issue=1|bibcode= 2008JEZB..310...15L}}</ref> There is no [[coelom]] at any stage.<ref name="RuppertFoxBarnesKamptozoa" />

In some species the larva is a [[trochophore]] which is [[plankton]]ic and feeds on floating food particles by using the two bands of cilia round its "equator" to sweep food into the mouth, which uses more cilia to drive them into the stomach, which uses further cilia to expel undigested remains through the anus.<ref name="RuppertFoxBarnes2004MolluscaTroch">{{cite book | author1=Ruppert, E.E. | author2=Fox, R.S. | author3=Barnes, R.D. | name-list-style=amp| title=Invertebrate Zoology | chapter=Mollusca | publisher=Brooks / Cole | edition=7th | isbn=0-03-025982-7 | year=2004 | pages=[https://archive.org/details/isbn_9780030259821/page/290 290–291] | url=https://archive.org/details/isbn_9780030259821/page/290 }}</ref> In some species of the [[genus|genera]] ''[[Loxosomella]]'' and ''[[Loxosoma]]'', the larva produces one or two buds that separate and form new individuals, while the trochophore disintegrates. However, most produce a larva with sensory tufts at the top and front, a pair of pigment-cup [[ocelli]] ("little eyes"), a pair of [[protonephridia]], and a large, cilia-bearing foot at the bottom.<ref name="Nielsen2001InEncOfLifeSciEntoprocta" /> After settling, the foot and frontal tuft attach to the surface. Larvae of most species undergo a complex [[metamorphosis]], and the internal organs may rotate by up to 180°, so that the mouth and anus both point upwards.<ref name="RuppertFoxBarnesKamptozoa" />

All species can produce [[cloning|clone]]s by [[budding]]. Colonial species produce new zooids from the stolon or from the stalks, and can form large colonies in this way.<ref name="RuppertFoxBarnesKamptozoa" /> In solitary species, clones form on the floor of the atrium, and are released when their organs are developed.<ref name="Nielsen2001InEncOfLifeSciEntoprocta" />

==Taxonomy==
{{See also|List of bilaterial animal orders}}
The phylum consists of about 150 recognized species, grouped into 4 [[family (biology)|families]]:<ref name="RuppertFoxBarnesKamptozoa" /><ref name="ITISEntoprocta" />

{| class="wikitable"
|- align="center"
! Family !! Barentsiidae !! Pedicellinidae !! Loxokalypodidae !! Loxosomatidae
|- align="left"
! align="center" | Genera
| ''[[Barentsia]]'', ''[[Coriella]]'', ''[[Pedicellinopsis]]'', ''[[Pseudopedicellina]]'', ''[[Urnatella]]''<ref>{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=708693|title=ITIS Standard Report Page: Barentsiidae|year=2006|access-date=2009-09-14}}</ref>
| ''[[Chitaspis]]'', ''[[Loxosomatoides]]'', ''[[Myosoma]]'', ''[[Pedicellina]]''<ref>{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156738|title=ITIS Standard Report Page: Pedicellinidae|year=2006|access-date=2009-09-14}}</ref>
| ''[[Loxokalypus]]''<ref>{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=708694|title=ITIS Standard Report Page: Loxokalypodidae|year=2006|access-date=2009-09-14}}</ref>
| ''[[Loxocore]]'', ''[[Loxomitra]]'', ''[[Loxosoma]]'', ''[[Loxosomella]]'',<!-- ZoolSci25:1171. --> ''[[Loxosomespilon]]''<ref>{{cite web|url=https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=156734|title=ITIS Standard Report Page: Loxosomatidae|year=2006|access-date=2009-09-14}}</ref>
|- align="center"
! Colonial<ref name="Wasson1997SystematicRevision">{{cite journal|last=Wasson|first=K.|year=1997|title=Systematic revision of colonial kamptozoans (entoprocts) of the Pacific coast of North America|journal=Zoological Journal of the Linnean Society|volume=121|issue=1|pages=1–63|doi=10.1111/j.1096-3642.1997.tb00146.x|doi-access=free}}</ref>
| colspan="3" | Colonial || Solitary
|- align="center"
! Septum between calyx and stalk<ref name="Wasson1997SystematicRevision" />
| colspan="2" | Yes || colspan="2" | No
|- align="center"
! Star-cell organ<ref name="Wasson1997SystematicRevision" />
| colspan="2" | Yes || colspan="2" | No
|- align="center"
! Anus on cone<ref name="RuppertFoxBarnesKamptozoa" />
| colspan="2" | No || colspan="2" | Yes
|- align="center"
! Stolons present<ref name="Wasson1997SystematicRevision" />
| colspan="2" | Yes || No, colonies grow on shared baseplate || Not colonial
|- align="center"
! Segmented stems<ref name="RuppertFoxBarnesKamptozoa" /><ref name="Wasson1997SystematicRevision" />
| Yes || colspan="3" | No
|}

==Evolutionary history==

===Fossil record===
[[File:Dinomischus.png| thumb | right | 120px | The Mid-[[Cambrian]] ''[[Dinomischus]]'' was once hailed as the earliest fossil entoproct,<ref name="SCM1977NewEntoproctlikeOrganism" /> but the classification is uncertain<ref name="ToddTaylor1992FirstFossilEntoproct" />]]
Since entoprocts are small and soft-bodied, fossils have been extremely rare.<ref name="ToddTaylor1992FirstFossilEntoproct" /> In 1977, [[Simon Conway Morris]] provided the first description of ''[[Dinomischus]]'', a sessile animal with calyx, stalk and holdfast, found in [[Canada]]'s [[Burgess Shale]], which was formed about {{ma|505}}. Conway Morris regarded this animal as the earliest known entoproct, since its mouth and anus lay inside a ring of structures above the calyx, but noted that these structures were flat and rather stiff, while the tentacles of modern entoprocts are flexible and have a round cross-section.<ref name="SCM1977NewEntoproctlikeOrganism">{{cite journal
 | author = Conway Morris, S. | year = 1977 | title = A new entoproct-like organism from the Burgess Shale of British Columbia
 | url = http://palaeontology.palass-pubs.org/pdf/Vol%2020/Pages%20833-845.pdf | archive-url = https://web.archive.org/web/20110716055640/http://palaeontology.palass-pubs.org/pdf/Vol%2020/Pages%20833-845.pdf | url-status = usurped | archive-date = July 16, 2011 | access-date=13 Sep 2009
 | journal = [[Palaeontology (journal)|Palaeontology]] | volume = 20 |issue=4 | pages = 833–845 
}}</ref>

In 1992 J.A. Todd and P.D. Taylor concluded that ''Dinomischus'' was not an entoproct, because it did not have the typical rounded, flexible tentacles, and the fossils showed no other features that clearly resembled those of entoprocts. In their opinion, the earliest fossil entoprocts were specimens they found from Late [[Jurassic]] rocks in England. These resemble the modern colonial genus ''[[Barentsia]]'' in many ways, including: upright zooids linked by a network of stolons encrusting the surface to which the colony is attached; straight stalks joined to the stolons by bulky sockets with transverse bands of wrinkles; overall size and proportions similar to that of modern species of ''Barentsia''.<ref name="ToddTaylor1992FirstFossilEntoproct">{{cite journal|last=Todd|first=J.A.|author2=Taylor, P.D.|date=July 1992|title=The first fossil entoproct|journal=Naturwissenschaften|volume=79|issue=7|pages=311–314| doi=10.1007/BF01138708|bibcode=1992NW.....79..311T|s2cid=44229586}}</ref>

Another species, ''[[Cotyledion tylodes]]'', first described in 1999, was larger than extant entoprocts, reaching 8–56&nbsp;mm in height, and unlike modern species, was "armored" with sclerites, scale-like structures. ''C. tylodes'' did have a similar [[sessility (zoology)|sessile]] lifestyle to modern entoprocts. The identified fossils of ''C. tylodes'' were found in 520-million-year-old rocks from southern China. This places early entoprocts in the period of the [[Cambrian explosion]].<ref>Sid Perkins, "ScienceShot: Fossils of Enigmatic Sea Creature Emerge", ScienceNOW, January 17, 2013</ref>

===Family tree===
When entoprocts were discovered in the nineteenth century, they and bryozoans (ectoprocts) were regarded as classes within the phylum [[Bryozoa]], because both groups were [[sessility (zoology)|sessile]] animals that [[filter feeder|filter-fed]] by means of a "crown" of tentacles that bore [[cilia]]. However, from 1869 onwards, increasing awareness of differences, including the position of the entoproct [[anus]] inside the feeding structure and the difference in the early [[Cleavage (embryo)|pattern of division]] of cells in their [[embryo]]s, caused scientists to regard the two groups as separate [[phylum|phyla]].<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics">{{cite journal|last=Hausdorf|first=B.|author2=Helmkampf, M. |author3=Meyer, A. |date=December 2007|title=Spiralian phylogenomics supports the resurrection of Bryozoa comprising Ectoprocta and Entoprocta|journal=Molecular Biology and Evolution|volume=24|issue=12|pages=2723–2729|doi=10.1093/molbev/msm214|pmid=17921486 |display-authors=etal|doi-access=free}}</ref> "Bryozoa" then became just an alternative name for ectoprocts, in which the anus is outside the feeding organ.<ref name="Halanych2004AnimalPhylogeny">{{cite journal|last=Halanych|first=K.M..|year=2004|title=The new view of animal phylogeny|journal= Annual Review of Ecology, Evolution, and Systematics|volume=35|pages=229–256|url=http://www-fourier.ujf-grenoble.fr/~dpiau/cdem/130124b.pdf | doi=10.1146/annurev.ecolsys.35.112202.130124}}</ref> However, studies by one team in 2007 and 2008 argue for sinking Entoprocta into Bryozoa as a [[class (biology)|class]], and resurrecting ''Ectoprocta'' as a name for the currently identified bryozoans.<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics" /><ref name="HelmkampfBruchhausHausdorf2008PhylogenOfLophophorates">{{cite journal|last=Helmkampf|first=M.|author2=Bruchhaus, I. |author3=Hausdorf, B. |date=22 August 2008|title=Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept|journal=Proceedings of the Royal Society B |volume=275|pages=1927–1933|doi=10.1098/rspb.2008.0372|pmid=18495619|issue=1645|pmc=2593926}}</ref>

The consensus of studies from 1996 onwards has been that entoprocts are part of the [[Trochozoa]], a [[protostome]] "superphylum" whose members are united in having as their most basic larval form the [[trochophore]] type. The trochozoa also include [[mollusc]]s, [[annelid]]s, [[flatworm]]s, [[nemertine]]s and others. However, scientists disagree about which phylum is mostly closely related to enctoprocts within the trochozoans.<ref>{{cite book|last=Haszprunar|first=G.|author2=Schander, C. |author3=Halanych, K.M. |title=Phylogeny and evolution of the Mollusca|editor=Ponder, W.F. |editor2=Lindberg, D.R.|publisher=University of California Press|year=2008|pages=19–22|chapter=Relationships of Higher Molluscan Taxa|isbn=978-0-520-25092-5|chapter-url=https://books.google.com/books?id=nm0IZAQQ6S0C&q=Entoprocta+kamptozoa+phylogeny&pg=RA1-PA6-IA15|access-date=13 Sep 2009}}</ref> An analysis in 2008 re-introduced the pre-1869 meaning of the term "Bryozoa", for a group in which entoprocts and ectoprocts are each other's closest relatives.<ref name="HausdorfHelmkampfMeyer2007Spiralian Phylogenomics" />

==Ecology==

===Distribution and habitats===
All species are sessile.<ref name="RuppertFoxBarnesKamptozoa" /> While the great majority are marine, two species live in freshwater: ''[[Loxosomatoides sirindhornae]]'', reported in 2004 in central [[Thailand]], and ''[[Urnatella gracilis]]'', found in all the continents except [[Antarctica]].<ref name="Wood2005LoxosomatoidesSirindhornae" /> Colonial species are found in all the oceans, living on rocks, shells, [[alga]]e and underwater buildings.<ref name="RuppertFoxBarnesKamptozoa" /> The solitary species, which are marine,<ref name="Wood2005LoxosomatoidesSirindhornae" /> live on other animals that feed by producing water currents, such as [[sponge]]s, [[ectoproct]]s and sessile [[annelid]]s.<ref name="Nielsen2001InEncOfLifeSciEntoprocta" /> The majority of species live no deeper than 50&nbsp;meters, but a few species are found in the deep ocean.<ref>[http://www.deepseanews.com/2014/08/a-new-inside-anus-found-very-deep/ A New Inside Anus Found Very Deep]</ref>

===Interaction with other organisms===
Some species of [[nudibranch]]s ("sea slugs"), particularly those of the genus ''[[Trapania]]'', as well as [[turbellarian]] [[flatworm]]s, prey on entoprocts.<ref>{{cite journal|last= Canning|first=M.H.|author2=Carlton, J.T.|date=11 May 2005|title=Predation on kamptozoans (Entoprocta)|journal=Invertebrate Biology|volume=119|issue=4|pages=386–387|doi=10.1111/j.1744-7410.2000.tb00107.x}}</ref>

Small colonies of the freshwater entoproct ''[[Urnatella gracilis]]'' have been found living on the aquatic larvae of the [[dobsonfly]] ''[[Corydalus cornutus]]''. The ectoprocts gain a means of dispersal, protection from predators and possibly a source of water that is rich in [[oxygen]] and nutrients, as colonies often live next to the gills of the larval flies.<ref>{{cite journal|doi=10.2307/1467150|last=Tracy|first=B.H.|author2=Hazelwood, D.H.|date=November 1983|title=The phoretic association of ''Urnatella gracilis'' (Entoprocta: Urnatellidae) and ''Nanocladius downesi'' (Diptera: Chironomidae) on ''Corydalus cornutus'' (Megaloptera: Corydalidae)|journal=Freshwater Invertebrate Biology|volume=2|issue=4|pages=186–191|publisher=The North American Benthological Society|jstor=1467150|s2cid=87592771}}</ref> In the [[White Sea]], the non-colonial entoproct ''[[Loxosomella nordgaardi]]'' prefers to live attached to [[bryozoa]]n (ectoproct) colonies, mainly on the edges of colonies or in the "chimneys", gaps by which large bryozoan colonies expel water from which they have sieved food. Observation suggests that both the entoprocts and the bryozoans benefit from the association: each enhances the water flow that the other needs for feeding; and the longer [[cilia]] of the entoprocts may help them to capture different food from that caught by the bryozoans, so that the animals do not compete for the same food.<ref>{{cite journal|last=Yakovis|first=E.L.|date=December 2002|title=Substrate preferences of a non-colonial kamptozoan, and its interactions with bryozoan hosts|journal=Marine Biology|volume=141|issue=6|pages=1109–1115|doi=10.1007/s00227-002-0902-x|bibcode=2002MarBi.141.1109E |s2cid=85767673}}</ref>

Entoprocts are small and have been little studied by zoologists. Hence it is difficult to determine whether a specimen belongs to a species that already occurs in the same area or is an [[invasive species|invader]], possibly as a result of human activities.<ref>{{cite journal|last1=Wasson|first1=K.|last2=Von Holle|first2= B.|last3=Toft|first3= J.|last4=Ruiz| first4=G.|date=March 2000|title=Detecting invasions of marine organisms: kamptozoan case histories|journal=Biological Invasions|volume=2|issue=1|pages=59–74|doi=10.1023/A:1010049907067|s2cid=38120150}}</ref>

==References==
{{Reflist|30em}}

==Further reading==
*{{cite book|last=Nielsen|first=C.|title=Synopsis of the British Fauna No. 41|editor=Kermack, D.M. |editor2=Barnes, R.S.K.|publisher=Brill|location=Leiden|year=1989|chapter=Entoprocts}}

==External links==
* {{Commons category-inline|Entoprocta}}
* [http://www.earthlife.net/inverts/entoprocta.html Information on Entoprocta from earthlife.net]

{{Animalia}}
{{Life on Earth}}
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[[Category:Entoprocta| ]]
[[Category:Protostome phyla]]
[[Category:Extant Cambrian first appearances]]