Jump to content

Coelom: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
OAbot (talk | contribs)
Bots
430,849 edits
m Open access bot: pmc updated in citation with #oabot.
œ
Tag: Reverted
Line 1: Line 1:
{{Short description|The main body cavity in many animals}}
{{Short description|The main body cavity in many animals}}
{{Infobox anatomy
{{Infobox anatomy
|Name = Coelom
|Name = Cœlom
|Greek = koilōma
|Greek = koilōma
|Image = Annelid redone w white background.svg
|Image = Annelid redone w white background.svg
|Caption = Cross-section of an [[oligochaete worm]]. The worm's '''body cavity''' surrounds the central [[typhlosole]].
|Caption = Cross-section of an [[oligochaete worm]]. The worm's '''body cavity''' surrounds the central [[typhlosole]].
| pronunciation = ({{IPAc-en|ˈ|s|iː|l|əm}} {{respell|SEE|ləm}}, plural '''coeloms''' or '''coelomata''' {{IPAc-en|s|iː|ˈ|l|oʊ|m|ə|t|ə}} {{respell|see|LOH|mə-tə}})
| pronunciation = ({{IPAc-en|ˈ|s|iː|l|əm}} {{respell|SEE|ləm}}, plural '''cœloms''' or '''cœlomata''' {{IPAc-en|s|iː|ˈ|l|oʊ|m|ə|t|ə}} {{respell|see|LOH|mə-tə}})
}}
}}


The '''coelom''' (or '''celom''')<ref>{{cite Merriam-Webster|celom}}</ref> is the main [[body cavity]] in many animals<ref>{{cite web |url=http://encyclopedia2.thefreedictionary.com/coelom |title=coelom |via=[[The Free Dictionary]]}}</ref> and is positioned inside the [[Body (biology)|body]] to surround and contain the [[digestive tract]] and other [[Organ (biology)|organs]]. In some [[animal]]s, it is lined with [[mesothelium]]. In other animals, such as [[molluscs]], it remains undifferentiated. In the past, and for practical purposes, coelom characteristics have been used to classify [[bilaterian]] animal phyla into informal groups.
The '''cœlom''' (or '''celom''')<ref>{{cite Merriam-Webster|celom}}</ref> is the main [[body cavity]] in many animals<ref>{{cite web |url=http://encyclopedia2.thefreedictionary.com/coelom |title=coelom |via=[[The Free Dictionary]]}}</ref> and is positioned inside the [[Body (biology)|body]] to surround and contain the [[digestive tract]] and other [[Organ (biology)|organs]]. In some [[animal]]s, it is lined with [[mesothelium]]. In other animals, such as [[molluscs]], it remains undifferentiated. In the past, and for practical purposes, cœlom characteristics have been used to classify [[bilaterian]] animal phyla into informal groups.


== Etymology ==
== Etymology ==
The term ''coelom'' derives from the [[Ancient Greek]] word {{wikt-lang|grc|κοιλία}} ({{grc-transl|κοιλία}}) 'cavity'.<ref>{{Cite book | title=Abrégé du dictionnaire grec français | last=Bailly | first=Anatole | date=1981-01-01 | publisher=Hachette | isbn=2010035283 | location=Paris | oclc=461974285}}</ref><ref>{{Cite web | url=http://www.tabularium.be/bailly/ | title=Greek-french dictionary online | last=Bailly | first=Anatole | website=www.tabularium.be | access-date=2018-01-14}}</ref><ref>{{cite EB1911|wstitle=Coelom and Serous Membranes|volume=6|page=642}}</ref>
The term ''cœlom'' derives from the [[Ancient Greek]] word {{wikt-lang|grc|κοιλία}} ({{grc-transl|κοιλία}}) 'cavity'.<ref>{{Cite book | title=Abrégé du dictionnaire grec français | last=Bailly | first=Anatole | date=1981-01-01 | publisher=Hachette | isbn=2010035283 | location=Paris | oclc=461974285}}</ref><ref>{{Cite web | url=http://www.tabularium.be/bailly/ | title=Greek-french dictionary online | last=Bailly | first=Anatole | website=www.tabularium.be | access-date=2018-01-14}}</ref><ref>{{cite EB1911|wstitle=Cœlom and Serous Membranes|volume=6|page=642}}</ref>


== Structure ==
== Structure ==


=== Development ===
=== Development ===
The coelom is the mesodermally lined cavity between the gut and the outer body wall.
The cœlom is the mesodermally lined cavity between the gut and the outer body wall.


During the [[embryogenesis|development of the embryo]], coelom formation begins in the [[gastrulation]] stage. The developing digestive tube of an [[embryo]] forms as a blind pouch called the [[archenteron]].
During the [[embryogenesis|development of the embryo]], cœlom formation begins in the [[gastrulation]] stage. The developing digestive tube of an [[embryo]] forms as a blind pouch called the [[archenteron]].


In [[protostomes]], the coelom forms by a process known as [[schizocoely]].<ref name="Lüter2000">{{Cite journal |last=Lüter |first=Carsten |date=2000-06-01 |title=The origin of the coelom in Brachiopoda and its phylogenetic significance |journal=Zoomorphology |language=en |volume=120 |issue=1 |pages=15–28 |doi=10.1007/s004359900019 |s2cid=24929317 |issn=1432-234X}}</ref> The [[archenteron]] initially forms, and the [[mesoderm]] splits into two layers: the first attaches to the body wall or [[ectoderm]], forming the [[parietal layer]] and the second surrounds the [[endoderm]] or [[alimentary canal]] forming the [[visceral layer]]. The space between the parietal layer and the visceral layer is known as the coelom or body cavity.
In [[protostomes]], the cœlom forms by a process known as [[schizocoely]].<ref name="Lüter2000">{{Cite journal |last=Lüter |first=Carsten |date=2000-06-01 |title=The origin of the cœlom in Brachiopoda and its phylogenetic significance |journal=Zoomorphology |language=en |volume=120 |issue=1 |pages=15–28 |doi=10.1007/s004359900019 |s2cid=24929317 |issn=1432-234X}}</ref> The [[archenteron]] initially forms, and the [[mesoderm]] splits into two layers: the first attaches to the body wall or [[ectoderm]], forming the [[parietal layer]] and the second surrounds the [[endoderm]] or [[alimentary canal]] forming the [[visceral layer]]. The space between the parietal layer and the visceral layer is known as the cœlom or body cavity.


In [[deuterostomes]], the coelom forms by [[enterocoely]].<ref name="Lüter2000"/> The archenteron wall produces buds of [[mesoderm]], and these mesodermal [[diverticula]] hollow to become the coelomic cavities. Deuterostomes are therefore known as ''enterocoelomates''. Examples of deuterostome coelomates belong to three major clades: [[chordates]] ([[vertebrate]]s, [[tunicate]]s, and [[lancelet]]s), [[echinoderms]] ([[starfish]], [[sea urchin]]s, [[Holothuroidea|sea cucumber]]s), and [[hemichordates]] ([[acorn worm]]s and [[graptolite]]s).
In [[deuterostomes]], the cœlom forms by [[enterocoely]].<ref name="Lüter2000"/> The archenteron wall produces buds of [[mesoderm]], and these mesodermal [[diverticula]] hollow to become the cœlomic cavities. Deuterostomes are therefore known as ''enterocœlomates''. Examples of deuterostome cœlomates belong to three major clades: [[chordates]] ([[vertebrate]]s, [[tunicate]]s, and [[lancelet]]s), [[echinoderms]] ([[starfish]], [[sea urchin]]s, [[Holothuroidea|sea cucumber]]s), and [[hemichordates]] ([[acorn worm]]s and [[graptolite]]s).


=== Origins ===
=== Origins ===
The [[evolution]]ary origin of the coelom is uncertain. The oldest known animal to have had a body cavity was the ''[[Vernanimalcula]]''. Current hypothesis include:{{citation needed|date=November 2018}}<ref>{{Cite web|url=http://faculty.college-prep.org/~bernie/sciproject/project/Kingdoms/Animal%20Kingdom%20-%205/Local%20copy/evolution.html |title=Origins and Evolution of Animals |archive-url=https://web.archive.org/web/20181112211737/http://faculty.college-prep.org/~bernie/sciproject/project/Kingdoms/Animal%20Kingdom%20-%205/Local%20copy/evolution.html#coelomates |archive-date=2018-11-12}}</ref>
The [[evolution]]ary origin of the cœlom is uncertain. The oldest known animal to have had a body cavity was the ''[[Vernanimalcula]]''. Current hypothesis include:{{citation needed|date=November 2018}}<ref>{{Cite web|url=http://faculty.college-prep.org/~bernie/sciproject/project/Kingdoms/Animal%20Kingdom%20-%205/Local%20copy/evolution.html |title=Origins and Evolution of Animals |archive-url=https://web.archive.org/web/20181112211737/http://faculty.college-prep.org/~bernie/sciproject/project/Kingdoms/Animal%20Kingdom%20-%205/Local%20copy/evolution.html#coelomates |archive-date=2018-11-12}}</ref>
* The acoelomate theory, which states that coelom evolved from an acoelomate ancestor.
* The acœlomate theory, which states that cœlom evolved from an acœlomate ancestor.
* The enterocoel theory, which states that coelom evolved from gastric pouches of [[cnidaria]]n ancestors. This is supported by research on [[flatworm]]s{{citation needed|date=March 2021}} and small worms recently discovered{{clarification needed|date=March 2021}} in marine fauna{{citation needed|date=March 2021}} ("coelom"<ref>{{Cite web|url=http://www.answers.com/body%20cavity |title=McGraw-Hill Dictionary of Scientific and Technical Terms |website=[[Answers.com]] |archive-url=https://web.archive.org/web/20141220091027/http://www.answers.com/topic/body-cavity-1 |archive-date=2014-12-20}}</ref>).
* The enterocoel theory, which states that cœlom evolved from gastric pouches of [[cnidaria]]n ancestors. This is supported by research on [[flatworm]]s{{citation needed|date=March 2021}} and small worms recently discovered{{clarification needed|date=March 2021}} in marine fauna{{citation needed|date=March 2021}} ("coelom"<ref>{{Cite web|url=http://www.answers.com/body%20cavity |title=McGraw-Hill Dictionary of Scientific and Technical Terms |website=[[Answers.com]] |archive-url=https://web.archive.org/web/20141220091027/http://www.answers.com/topic/body-cavity-1 |archive-date=2014-12-20}}</ref>).


== Functions ==
== Functions ==
A coelom can absorb shock or provide a [[hydrostatic skeleton]]. It can also support an [[immune system]] in the form of [[coelomocyte]]s that may either be attached to the wall of the coelom or may float about in it freely. The coelom allows muscles to grow independently of the body wall — this feature can be seen in the digestive tract of [[tardigrade]]s (water bears) which is suspended within the body in the [[mesentery]] derived from a mesoderm-lined coelom.
A cœlom can absorb shock or provide a [[hydrostatic skeleton]]. It can also support an [[immune system]] in the form of [[cœlomocyte]]s that may either be attached to the wall of the cœlom or may float about in it freely. The cœlom allows muscles to grow independently of the body wall — this feature can be seen in the digestive tract of [[tardigrade]]s (water bears) which is suspended within the body in the [[mesentery]] derived from a mesoderm-lined cœlom.


== Coelomic fluid ==
== Cœlomic fluid ==
The fluid inside the coelom is known as coelomic fluid. This is circulated by mesothelial [[cilia]] or by contraction of muscles in the body wall.{{clarify|date=June 2018|reason=http://www.citycollegekolkata.org/online_course_materials/Evolution_of_Coelom.pdf}}<ref name=Ruppert>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |page=205 }}</ref> The coelomic fluid serves several functions: it acts as a hydroskeleton; it allows free movement and growth of internal organs; it serves for transport of gases, nutrients and waste products around the body; it allows storage of sperm and eggs during maturation; and it acts as a reservoir for waste.<ref name=Dorit>{{cite book |title=Zoology |url=https://archive.org/details/zoology0000dori |url-access=registration |last1=Dorit |first1=R. L. |last2=Walker |first2=W. F. |last3=Barnes |first3=R. D. |year=1991 |publisher=Saunders College Publishing |isbn=978-0-03-030504-7 |page=[https://archive.org/details/zoology0000dori/page/190 190] }}</ref>
The fluid inside the cœlom is known as cœlomic fluid. This is circulated by mesothelial [[cilia]] or by contraction of muscles in the body wall.{{clarify|date=June 2018|reason=http://www.citycollegekolkata.org/online_course_materials/Evolution_of_Cœlom.pdf}}<ref name=Ruppert>{{cite book |title=Invertebrate Zoology, 7th edition |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard, S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |page=205 }}</ref> The cœlomic fluid serves several functions: it acts as a hydroskeleton; it allows free movement and growth of internal organs; it serves for transport of gases, nutrients and waste products around the body; it allows storage of sperm and eggs during maturation; and it acts as a reservoir for waste.<ref name=Dorit>{{cite book |title=Zoology |url=https://archive.org/details/zoology0000dori |url-access=registration |last1=Dorit |first1=R. L. |last2=Walker |first2=W. F. |last3=Barnes |first3=R. D. |year=1991 |publisher=Saunders College Publishing |isbn=978-0-03-030504-7 |page=[https://archive.org/details/zoology0000dori/page/190 190] }}</ref>


== Classification in zoology ==
== Classification in zoology ==
{{Further|Body cavity}}
{{Further|Body cavity}}
In the past, some zoologists grouped [[bilaterian]] animal phyla based on characteristics related to the coelom for practical purposes, knowing, and explicitly stating, that these groups were ''not'' [[Phylogenetics|phylogenetically]] related. Animals were classified in three informal groups according to the type of body cavity they possess, in a non-taxonomic, utilitarian way, as the Acoelomata, Pseudocoelomata, and Coelomata. These groups were never intended to represent related animals, or a sequence of evolutionary traits.
In the past, some zoologists grouped [[bilaterian]] animal phyla based on characteristics related to the cœlom for practical purposes, knowing, and explicitly stating, that these groups were ''not'' [[Phylogenetics|phylogenetically]] related. Animals were classified in three informal groups according to the type of body cavity they possess, in a non-taxonomic, utilitarian way, as the Acœlomata, Pseudocœlomata, and Cœlomata. These groups were never intended to represent related animals, or a sequence of evolutionary traits.


However, although this scheme was followed by a number of college textbooks and some general classifications, it is now almost totally abandoned as a formal classification. Indeed, as late as 2010, one author of a [[molecular phylogeny]] study mistakenly called this classification scheme the "traditional, morphology-based phylogeny".<ref>Nielsen, C. (2010). "[http://www.palaeodiversity.org/pdf/03Suppl/Supplement_Nielsen.pdf The 'new phylogeny'. What is new about it?]" ''Palaeodiversity'' 3, 149–150.</ref>
However, although this scheme was followed by a number of college textbooks and some general classifications, it is now almost totally abandoned as a formal classification. Indeed, as late as 2010, one author of a [[molecular phylogeny]] study mistakenly called this classification scheme the "traditional, morphology-based phylogeny".<ref>Nielsen, C. (2010). "[http://www.palaeodiversity.org/pdf/03Suppl/Supplement_Nielsen.pdf The 'new phylogeny'. What is new about it?]" ''Palaeodiversity'' 3, 149–150.</ref>
[[File:Figure 27 02 05.jpg|thumb|right|upright=2|alt=An illustration describing the classification of tripoblasts.|Classification of tripoblasts based on body cavities]]
[[File:Figure 27 02 05.jpg|thumb|right|upright=2|alt=An illustration describing the classification of tripoblasts.|Classification of tripoblasts based on body cavities]]


'''Coelomate''' animals or '''Coelomata''' (also known as eucoelomates – "true coelom") have a body cavity called a coelom with a complete lining called [[peritoneum]] derived from mesoderm (one of the three [[germ layer|primary tissue layers]]). The complete mesoderm lining allows organs to be attached to each other so that they can be suspended in a particular order while still being able to move freely within the cavity. Most bilateral animals, including all the [[vertebrate]]s, are coelomates.
'''Cœlomate''' animals or '''Cœlomata''' (also known as eucœlomates – "true cœlom") have a body cavity called a cœlom with a complete lining called [[peritoneum]] derived from mesoderm (one of the three [[germ layer|primary tissue layers]]). The complete mesoderm lining allows organs to be attached to each other so that they can be suspended in a particular order while still being able to move freely within the cavity. Most bilateral animals, including all the [[vertebrate]]s, are cœlomates.


'''Pseudocoelomate''' animals have a '''pseudocoelom''' (literally "false cavity"), which is a fluid filled body cavity. Tissue derived from mesoderm partly lines the fluid filled body cavity of these animals. Thus, although organs are held in place loosely, they are not as well organized as in a coelomate. All pseudocoelomates are [[protostome]]s; however, not all protostomes are pseudocoelomates. An example of a pseudocoelomate is the roundworm. pseudocoelomate animals are also referred to as [[Blastocoele|blastocoelomate]].
'''Pseudocœlomate''' animals have a '''pseudocœlom''' (literally "false cavity"), which is a fluid filled body cavity. Tissue derived from mesoderm partly lines the fluid filled body cavity of these animals. Thus, although organs are held in place loosely, they are not as well organized as in a cœlomate. All pseudocœlomates are [[protostome]]s; however, not all protostomes are pseudocœlomates. An example of a pseudocœlomate is the roundworm. pseudocœlomate animals are also referred to as [[Blastocoele|blastocœlomate]].


'''Acoelomate''' animals, like [[flatworm]]s, have no body cavity at all. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.
'''Acœlomate''' animals, like [[flatworm]]s, have no body cavity at all. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.


== Coelomates ==
== Cœlomates ==
Coeloms developed in [[triploblast]]s but were subsequently lost in several lineages. The lack of a coelom is correlated with a reduction in body size. Coelom is sometimes incorrectly used to refer to any developed digestive tract. Some organisms may not possess a coelom or may have a false coelom ([[Body cavity#Pseudocoelom|pseudocoelom]]). Animals having coeloms are called [[coelomate]]s, and those without are called [[acoelomate]]s. There are also subtypes of coelom:{{citation needed|date=February 2015}}
Cœloms developed in [[triploblast]]s but were subsequently lost in several lineages. The lack of a cœlom is correlated with a reduction in body size. Cœlom is sometimes incorrectly used to refer to any developed digestive tract. Some organisms may not possess a cœlom or may have a false cœlom ([[Body cavity#Pseudocoelom|pseudocœlom]]). Animals having cœloms are called [[cœlomate]]s, and those without are called [[acœlomate]]s. There are also subtypes of cœlom:{{citation needed|date=February 2015}}


* schizocoelom: develops from split in [[mesoderm]] found in [[annelids]], [[arthropods]] and [[molluscs]]
* schizocœlom: develops from split in [[mesoderm]] found in [[annelids]], [[arthropods]] and [[molluscs]]
* haemocoelom: true coelom reduced and cavity filled with blood found from [[arthropoda]] to [[mollusca]]
* haemocœlom: true cœlom reduced and cavity filled with blood found from [[arthropoda]] to [[mollusca]]
* enterocoelom: develops from wall of embryonic gut found from [[echinodermata]] to [[chordata]]
* enterocœlom: develops from wall of embryonic gut found from [[echinodermata]] to [[chordata]]


===Coelomate phyla===
===Cœlomate phyla===
According to [[Taxonomy of invertebrates (Brusca & Brusca, 2003)|Brusca and Brusca]],<ref name=Brusca>R. C. Brusca, G. J. Brusca. ''Invertebrates''. Sunderland, Massachusetts: Sinauer Associates, 2003 (2nd ed.), p.&nbsp;47, {{ISBN|0-87893-097-3}}.</ref> the following [[bilaterian]] [[phylum|phyla]] possess a coelom:
According to [[Taxonomy of invertebrates (Brusca & Brusca, 2003)|Brusca and Brusca]],<ref name=Brusca>R. C. Brusca, G. J. Brusca. ''Invertebrates''. Sunderland, Massachusetts: Sinauer Associates, 2003 (2nd ed.), p.&nbsp;47, {{ISBN|0-87893-097-3}}.</ref> the following [[bilaterian]] [[phylum|phyla]] possess a coelom:


*[[Nemertea]], traditionally viewed as acoelomates. Its coelom, called a rhynchocoel, lies above the digestive tract instead of around it like in other coelomate animals.<ref>[https://encyclopediaofarkansas.net/entries/nemertea-12880/ Nemertea]</ref>
*[[Nemertea]], traditionally viewed as acœlomates. Its cœlom, called a rhynchocœl, lies above the digestive tract instead of around it like in other cœlomate animals.<ref>[https://encyclopediaofarkansas.net/entries/nemertea-12880/ Nemertea]</ref>
*[[Priapulida]] appears to belong to the pseudocoelomate animals, but the possibility of it having a true coelom has still not been completely dismissed.<ref>[https://www.diva-portal.org/smash/get/diva2:1679890/FULLTEXT01.pdf Coelom development in the priapulid worm Priapulus caudatus]</ref>
*[[Priapulida]] appears to belong to the pseudocœlomate animals, but the possibility of it having a true cœlom has still not been completely dismissed.<ref>[https://www.diva-portal.org/smash/get/diva2:1679890/FULLTEXT01.pdf Cœlom development in the priapulid worm Priapulus caudatus]</ref>
*[[Onychophora]]
*[[Onychophora]]
*[[Tardigrada]]
*[[Tardigrada]]
Line 73: Line 73:
*[[Chordata]]
*[[Chordata]]


== Pseudocoelomates ==
== Pseudocœlomates ==
In some [[protostome]]s, the embryonic [[blastocoele]] persists as a body cavity. These protostomes have a fluid filled main body cavity unlined or partially lined with tissue derived from mesoderm.
In some [[protostome]]s, the embryonic [[blastocoele]] persists as a body cavity. These protostomes have a fluid filled main body cavity unlined or partially lined with tissue derived from mesoderm.


This fluid-filled space surrounding the internal [[organ (anatomy)|organ]]s serves several functions like distribution of nutrients and removal of waste or supporting the body as a [[hydrostatic skeleton]].
This fluid-filled space surrounding the internal [[organ (anatomy)|organ]]s serves several functions like distribution of nutrients and removal of waste or supporting the body as a [[hydrostatic skeleton]].


A '''pseudocoelomate''' or '''blastocoelomate''' is any [[invertebrate]] [[animal]] with a three-layered body and a [[Body cavity|pseudocoel]]. The coelom was apparently lost or reduced as a result of [[mutation]]s in certain types of [[gene]]s that affected early development. Thus, pseudocoelomates evolved from coelomates.<ref>Evers, Christine A., Lisa Starr. ''Biology:Concepts and Applications.'' 6th ed. United States:Thomson, 2006. {{ISBN|0-534-46224-3}}.</ref> "Pseudocoelomate" is no longer considered a valid [[Taxonomy (biology)|taxonomic group]], since it is not [[monophyletic]]. However, it is still used as a descriptive term.
A '''pseudocœlomate''' or '''blastocœlomate''' is any [[invertebrate]] [[animal]] with a three-layered body and a [[Body cavity|pseudocœl]]. The cœlom was apparently lost or reduced as a result of [[mutation]]s in certain types of [[gene]]s that affected early development. Thus, pseudocœlomates evolved from cœlomates.<ref>Evers, Christine A., Lisa Starr. ''Biology:Concepts and Applications.'' 6th ed. United States:Thomson, 2006. {{ISBN|0-534-46224-3}}.</ref> "Pseudocœlomate" is no longer considered a valid [[Taxonomy (biology)|taxonomic group]], since it is not [[monophyletic]]. However, it is still used as a descriptive term.


Important characteristics:
Important characteristics:
Line 96: Line 96:
* possibly [[pedomorphism]]
* possibly [[pedomorphism]]


===Pseudocoelomate phyla===
===Pseudocœlomate phyla===
Bilaterian pseudocoelomate phyla according to Brusca and Brusca,:<ref name=Brusca />
Bilaterian pseudocœlomate phyla according to Brusca and Brusca,:<ref name=Brusca />


*[[Nematoda]] (roundworms)
*[[Nematoda]] (roundworms)
Line 106: Line 106:
*[[Rotifera]], including [[Acanthocephala]] (spiny-headed worms)<ref>{{cite journal | url=https://www.sciencedirect.com/science/article/abs/pii/S105579031500370X | doi=10.1016/j.ympev.2015.11.017 | title=Phylogeny of Syndermata (Syn. Rotifera): Mitochondrial gene order verifies epizoic Seisonidea as sister to endoparasitic Acanthocephala within monophyletic Hemirotifera | date=2016 | last1=Sielaff | first1=Malte | last2=Schmidt | first2=Hanno | last3=Struck | first3=Torsten H. | last4=Rosenkranz | first4=David | last5=Mark Welch | first5=David B. | last6=Hankeln | first6=Thomas | last7=Herlyn | first7=Holger | journal=Molecular Phylogenetics and Evolution | volume=96 | pages=79–92 | bibcode=2016MolPE..96...79S }}</ref><ref>[https://web.archive.org/web/20180410121327id_/http://biosoc.pk/wp-content/uploads/2015/12/5-50-15-Rotifers-Safari.pdf Study of Rotifers of Safari Zoo Lake Lahore in Relation to Physico-chemical Parameters]</ref>
*[[Rotifera]], including [[Acanthocephala]] (spiny-headed worms)<ref>{{cite journal | url=https://www.sciencedirect.com/science/article/abs/pii/S105579031500370X | doi=10.1016/j.ympev.2015.11.017 | title=Phylogeny of Syndermata (Syn. Rotifera): Mitochondrial gene order verifies epizoic Seisonidea as sister to endoparasitic Acanthocephala within monophyletic Hemirotifera | date=2016 | last1=Sielaff | first1=Malte | last2=Schmidt | first2=Hanno | last3=Struck | first3=Torsten H. | last4=Rosenkranz | first4=David | last5=Mark Welch | first5=David B. | last6=Hankeln | first6=Thomas | last7=Herlyn | first7=Holger | journal=Molecular Phylogenetics and Evolution | volume=96 | pages=79–92 | bibcode=2016MolPE..96...79S }}</ref><ref>[https://web.archive.org/web/20180410121327id_/http://biosoc.pk/wp-content/uploads/2015/12/5-50-15-Rotifers-Safari.pdf Study of Rotifers of Safari Zoo Lake Lahore in Relation to Physico-chemical Parameters]</ref>


==Acoelomates==
==Acœlomates==
Acoelomates lack a fluid-filled body cavity between the body wall and digestive tract. This can cause some serious disadvantages. Fluid compression is negligible, while the tissue surrounding the organs of these animals will compress. Therefore, acoelomate organs are not protected from crushing forces applied to the animal's outer surface. The coelom can be used for diffusion of gases and metabolites etc. These creatures do not have this need, as the surface area to volume ratio is large enough to allow absorption of nutrients and gas exchange by diffusion alone, due to dorso-ventral flattening.
Acœlomates lack a fluid-filled body cavity between the body wall and digestive tract. This can cause some serious disadvantages. Fluid compression is negligible, while the tissue surrounding the organs of these animals will compress. Therefore, acœlomate organs are not protected from crushing forces applied to the animal's outer surface. The cœlom can be used for diffusion of gases and metabolites etc. These creatures do not have this need, as the surface area to volume ratio is large enough to allow absorption of nutrients and gas exchange by diffusion alone, due to dorso-ventral flattening.


*[[Flatworm]]s
*[[Flatworm]]s
* [[Limnognathia|Micrognathozoa]]
* [[Limnognathia|Micrognathozoa]]
*[[Mesozoa]]<ref>{{cite book | url=https://books.google.com/books?id=ss5ADwAAQBAJ&dq=seven+acoelomate+phyla&pg=PA156 | title=Biology of Non-Chordates | date=November 2017 | publisher=PHI Learning Pvt. | isbn=978-93-87472-01-3 }}</ref><ref>[https://core.ac.uk/download/pdf/234765327.pdf Comparative genomic studies on Dicyema japonicum: the phylogenetic position of dicyemids and the genomic adaptations to parasitic lifestyle]</ref>
*[[Mesozoa]]<ref>{{cite book | url=https://books.google.com/books?id=ss5ADwAAQBAJ&dq=seven+acoelomate+phyla&pg=PA156 | title=Biology of Non-Chordates | date=November 2017 | publisher=PHI Learning Pvt. | isbn=978-93-87472-01-3 }}</ref><ref>[https://core.ac.uk/download/pdf/234765327.pdf Comparative genomic studies on Dicyema japonicum: the phylogenetic position of dicyemids and the genomic adaptations to parasitic lifestyle]</ref>
*[[Xenacoelomorpha]]<ref>{{cite journal | url=https://www.nature.com/articles/ncomms2556 | doi=10.1038/ncomms2556 | title=Xenoturbella bocki exhibits direct development with similarities to Acoelomorpha | date=2013 | last1=Nakano | first1=Hiroaki | last2=Lundin | first2=Kennet | last3=Bourlat | first3=Sarah J. | last4=Telford | first4=Maximilian J. | last5=Funch | first5=Peter | last6=Nyengaard | first6=Jens R. | last7=Obst | first7=Matthias | last8=Thorndyke | first8=Michael C. | journal=Nature Communications | volume=4 | page=1537 | bibcode=2013NatCo...4.1537N | pmc=3586728 }}</ref><ref>[https://bioone.org/journals/zoological-science/volume-36/issue-5/zs190045/Xenacoelomorph-Specific-Hox-Peptides--Insights-into-the-Phylogeny-of/10.2108/zs190045.full Xenacoelomorph-Specific Hox Peptides: Insights into the Phylogeny of Acoels, Nemertodermatids, and Xenoturbellids]</ref>
*[[Xenacœlomorpha]]<ref>{{cite journal | url=https://www.nature.com/articles/ncomms2556 | doi=10.1038/ncomms2556 | title=Xenoturbella bocki exhibits direct development with similarities to Acœlomorpha | date=2013 | last1=Nakano | first1=Hiroaki | last2=Lundin | first2=Kennet | last3=Bourlat | first3=Sarah J. | last4=Telford | first4=Maximilian J. | last5=Funch | first5=Peter | last6=Nyengaard | first6=Jens R. | last7=Obst | first7=Matthias | last8=Thorndyke | first8=Michael C. | journal=Nature Communications | volume=4 | page=1537 | bibcode=2013NatCo...4.1537N | pmc=3586728 }}</ref><ref>[https://bioone.org/journals/zoological-science/volume-36/issue-5/zs190045/Xenacoelomorph-Specific-Hox-Peptides--Insights-into-the-Phylogeny-of/10.2108/zs190045.full Xenacoelomorph-Specific Hox Peptides: Insights into the Phylogeny of Acoels, Nemertodermatids, and Xenoturbellids]</ref>
*[[Gastrotricha]], traditionally viewed as blastocoelomates
*[[Gastrotricha]], traditionally viewed as blastocœlomates
*[[Entoprocta]], traditionally viewed as blastocoelomates
*[[Entoprocta]], traditionally viewed as blastocœlomates
*[[Gnathostomulida]], traditionally viewed as blastocoelomates
*[[Gnathostomulida]], traditionally viewed as blastocœlomates
*[[Cycliophora]]<ref>R.C.Brusca, G.J.Brusca 2003, p.&nbsp;379.</ref>
*[[Cycliophora]]<ref>R.C.Brusca, G.J.Brusca 2003, p.&nbsp;379.</ref>


Revision as of 22:21, 24 June 2024

Cœlom
Cross-section of an oligochaete worm. The worm's body cavity surrounds the central typhlosole.
Details
Pronunciation(/ˈsiːləm/ SEE-ləm, plural cœloms or cœlomata /siːˈloʊmətə/ see-LOH-mə-tə)
Identifiers
Greekkoilōma
Anatomical terminology

The cœlom (or celom)[1] is the main body cavity in many animals[2] and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, it remains undifferentiated. In the past, and for practical purposes, cœlom characteristics have been used to classify bilaterian animal phyla into informal groups.

Etymology

The term cœlom derives from the Ancient Greek word κοιλία (koilía) 'cavity'.[3][4][5]

Structure

Development

The cœlom is the mesodermally lined cavity between the gut and the outer body wall.

During the development of the embryo, cœlom formation begins in the gastrulation stage. The developing digestive tube of an embryo forms as a blind pouch called the archenteron.

In protostomes, the cœlom forms by a process known as schizocoely.[6] The archenteron initially forms, and the mesoderm splits into two layers: the first attaches to the body wall or ectoderm, forming the parietal layer and the second surrounds the endoderm or alimentary canal forming the visceral layer. The space between the parietal layer and the visceral layer is known as the cœlom or body cavity.

In deuterostomes, the cœlom forms by enterocoely.[6] The archenteron wall produces buds of mesoderm, and these mesodermal diverticula hollow to become the cœlomic cavities. Deuterostomes are therefore known as enterocœlomates. Examples of deuterostome cœlomates belong to three major clades: chordates (vertebrates, tunicates, and lancelets), echinoderms (starfish, sea urchins, sea cucumbers), and hemichordates (acorn worms and graptolites).

Origins

The evolutionary origin of the cœlom is uncertain. The oldest known animal to have had a body cavity was the Vernanimalcula. Current hypothesis include:[citation needed][7]

Functions

A cœlom can absorb shock or provide a hydrostatic skeleton. It can also support an immune system in the form of cœlomocytes that may either be attached to the wall of the cœlom or may float about in it freely. The cœlom allows muscles to grow independently of the body wall — this feature can be seen in the digestive tract of tardigrades (water bears) which is suspended within the body in the mesentery derived from a mesoderm-lined cœlom.

Cœlomic fluid

The fluid inside the cœlom is known as cœlomic fluid. This is circulated by mesothelial cilia or by contraction of muscles in the body wall.[clarification needed][9] The cœlomic fluid serves several functions: it acts as a hydroskeleton; it allows free movement and growth of internal organs; it serves for transport of gases, nutrients and waste products around the body; it allows storage of sperm and eggs during maturation; and it acts as a reservoir for waste.[10]

Classification in zoology

Further information: Body cavity

In the past, some zoologists grouped bilaterian animal phyla based on characteristics related to the cœlom for practical purposes, knowing, and explicitly stating, that these groups were not phylogenetically related. Animals were classified in three informal groups according to the type of body cavity they possess, in a non-taxonomic, utilitarian way, as the Acœlomata, Pseudocœlomata, and Cœlomata. These groups were never intended to represent related animals, or a sequence of evolutionary traits.

However, although this scheme was followed by a number of college textbooks and some general classifications, it is now almost totally abandoned as a formal classification. Indeed, as late as 2010, one author of a molecular phylogeny study mistakenly called this classification scheme the "traditional, morphology-based phylogeny".[11]

An illustration describing the classification of tripoblasts.
Classification of tripoblasts based on body cavities

Cœlomate animals or Cœlomata (also known as eucœlomates – "true cœlom") have a body cavity called a cœlom with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers). The complete mesoderm lining allows organs to be attached to each other so that they can be suspended in a particular order while still being able to move freely within the cavity. Most bilateral animals, including all the vertebrates, are cœlomates.

Pseudocœlomate animals have a pseudocœlom (literally "false cavity"), which is a fluid filled body cavity. Tissue derived from mesoderm partly lines the fluid filled body cavity of these animals. Thus, although organs are held in place loosely, they are not as well organized as in a cœlomate. All pseudocœlomates are protostomes; however, not all protostomes are pseudocœlomates. An example of a pseudocœlomate is the roundworm. pseudocœlomate animals are also referred to as blastocœlomate.

Acœlomate animals, like flatworms, have no body cavity at all. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.

Cœlomates

Cœloms developed in triploblasts but were subsequently lost in several lineages. The lack of a cœlom is correlated with a reduction in body size. Cœlom is sometimes incorrectly used to refer to any developed digestive tract. Some organisms may not possess a cœlom or may have a false cœlom (pseudocœlom). Animals having cœloms are called cœlomates, and those without are called acœlomates. There are also subtypes of cœlom:[citation needed]

Cœlomate phyla

According to Brusca and Brusca,[12] the following bilaterian phyla possess a coelom:

Pseudocœlomates

In some protostomes, the embryonic blastocoele persists as a body cavity. These protostomes have a fluid filled main body cavity unlined or partially lined with tissue derived from mesoderm.

This fluid-filled space surrounding the internal organs serves several functions like distribution of nutrients and removal of waste or supporting the body as a hydrostatic skeleton.

A pseudocœlomate or blastocœlomate is any invertebrate animal with a three-layered body and a pseudocœl. The cœlom was apparently lost or reduced as a result of mutations in certain types of genes that affected early development. Thus, pseudocœlomates evolved from cœlomates.[15] "Pseudocœlomate" is no longer considered a valid taxonomic group, since it is not monophyletic. However, it is still used as a descriptive term.

Important characteristics:

  • lack a vascular blood system
    • diffusion and osmosis circulate nutrients and waste products throughout the body.
  • lack a skeleton
    • hydrostatic pressure gives the body a supportive framework that acts as a skeleton.
  • no segmentation
  • body wall
    • epidermis and muscle
    • often syncytial
    • usually covered by a secreted cuticle
  • most are microscopic
  • parasites of almost every form of life (although some are free living)
  • eutely in some
  • loss of larval stage in some
  • possibly pedomorphism

Pseudocœlomate phyla

Bilaterian pseudocœlomate phyla according to Brusca and Brusca,:[12]

Acœlomates

Acœlomates lack a fluid-filled body cavity between the body wall and digestive tract. This can cause some serious disadvantages. Fluid compression is negligible, while the tissue surrounding the organs of these animals will compress. Therefore, acœlomate organs are not protected from crushing forces applied to the animal's outer surface. The cœlom can be used for diffusion of gases and metabolites etc. These creatures do not have this need, as the surface area to volume ratio is large enough to allow absorption of nutrients and gas exchange by diffusion alone, due to dorso-ventral flattening.

A body cavity is also absent in placozoans, cnidarians (jellyfish and allies) and the ctenophores (comb jellies), but these animals are neither bilaterians or triploblastic.

See also

References

  1. ^ "celom". Merriam-Webster.com Dictionary. Merriam-Webster.
  2. ^ "coelom" – via The Free Dictionary.
  3. ^ Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN 2010035283. OCLC 461974285.
  4. ^ Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved 2018-01-14.
  5. ^ Chisholm, Hugh, ed. (1911). "Cœlom and Serous Membranes" . Encyclopædia Britannica. Vol. 6 (11th ed.). Cambridge University Press. p. 642.
  6. ^ a b Lüter, Carsten (2000-06-01). "The origin of the cœlom in Brachiopoda and its phylogenetic significance". Zoomorphology. 120 (1): 15–28. doi:10.1007/s004359900019. ISSN 1432-234X. S2CID 24929317.
  7. ^ "Origins and Evolution of Animals". Archived from the original on 2018-11-12.
  8. ^ "McGraw-Hill Dictionary of Scientific and Technical Terms". Answers.com. Archived from the original on 2014-12-20.
  9. ^ Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 205. ISBN 978-81-315-0104-7.{{cite book}}: CS1 maint: multiple names: authors list (link)
  10. ^ Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing. p. 190. ISBN 978-0-03-030504-7.
  11. ^ Nielsen, C. (2010). "The 'new phylogeny'. What is new about it?" Palaeodiversity 3, 149–150.
  12. ^ a b R. C. Brusca, G. J. Brusca. Invertebrates. Sunderland, Massachusetts: Sinauer Associates, 2003 (2nd ed.), p. 47, ISBN 0-87893-097-3.
  13. ^ Nemertea
  14. ^ Cœlom development in the priapulid worm Priapulus caudatus
  15. ^ Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.
  16. ^ Sielaff, Malte; Schmidt, Hanno; Struck, Torsten H.; Rosenkranz, David; Mark Welch, David B.; Hankeln, Thomas; Herlyn, Holger (2016). "Phylogeny of Syndermata (Syn. Rotifera): Mitochondrial gene order verifies epizoic Seisonidea as sister to endoparasitic Acanthocephala within monophyletic Hemirotifera". Molecular Phylogenetics and Evolution. 96: 79–92. Bibcode:2016MolPE..96...79S. doi:10.1016/j.ympev.2015.11.017.
  17. ^ Study of Rotifers of Safari Zoo Lake Lahore in Relation to Physico-chemical Parameters
  18. ^ Biology of Non-Chordates. PHI Learning Pvt. November 2017. ISBN 978-93-87472-01-3.
  19. ^ Comparative genomic studies on Dicyema japonicum: the phylogenetic position of dicyemids and the genomic adaptations to parasitic lifestyle
  20. ^ Nakano, Hiroaki; Lundin, Kennet; Bourlat, Sarah J.; Telford, Maximilian J.; Funch, Peter; Nyengaard, Jens R.; Obst, Matthias; Thorndyke, Michael C. (2013). "Xenoturbella bocki exhibits direct development with similarities to Acœlomorpha". Nature Communications. 4: 1537. Bibcode:2013NatCo...4.1537N. doi:10.1038/ncomms2556. PMC 3586728.
  21. ^ Xenacoelomorph-Specific Hox Peptides: Insights into the Phylogeny of Acoels, Nemertodermatids, and Xenoturbellids
  22. ^ R.C.Brusca, G.J.Brusca 2003, p. 379.

Further reading

Retrieved from "https://en.wikipedia.org/w/index.php?title=Coelom&oldid=1230821110"