Coelom
| Coelom | |
|---|---|
oligochaete worm. The worm's body cavity surrounds the central typhlosole. | |
| Details | |
| Pronunciation | (/ˈsiːləm/ SEE-ləm, plural coeloms or coelomata /siːˈloʊmətə/ see-LOH-mə-tə) |
| Identifiers | |
| Greek | koilōma |
| Anatomical terminology] | |
The coelom (or celom)
Etymology
The term coelom derives from the Ancient Greek word κοιλία (koilía) 'cavity'.[3][4][5]
Structure
Development
The coelom is the mesodermally lined cavity between the gut and the outer body wall.
During the
In
In
Origins
The evolutionary origin of the coelom is uncertain. The oldest known animal to have had a body cavity was the Vernanimalcula. Current hypothesis include:[citation needed][7]
- The acoelomate theory, which states that coelom evolved from an acoelomate ancestor.
- The enterocoel theory, which states that coelom evolved from gastric pouches of cnidarian ancestors. This is supported by research on flatworms[citation needed] and small worms recently discovered[clarification needed] in marine fauna[citation needed] ("coelom"[8]).
Functions
A coelom can absorb shock or provide a hydrostatic skeleton. It can also support an immune system in the form of coelomocytes 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 tardigrades (water bears) which is suspended within the body in the mesentery derived from a mesoderm-lined coelom.
Coelomic fluid
The fluid inside the coelom is known as coelomic fluid. This is circulated by mesothelial
Classification in zoology
In the past, some zoologists grouped
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
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 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 coelomates.
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
Acoelomate animals, like flatworms, have no body cavity at all. Semi-solid mesodermal tissues between the gut and body wall hold their organs in place.
Coelomates
Coeloms developed in
- schizocoelom: develops from split in molluscs
- haemocoelom: true coelom reduced and cavity filled with blood found from arthropoda to mollusca
- enterocoelom: develops from wall of embryonic gut found from chordata
Coelomate phyla
According to
- Nemertea, traditionally viewed as acoelomates. Its coelom, called a rhynchocoel, lies above the digestive tract instead of around it like in other coelomate animals.[13]
- Priapulida appears to belong to the pseudocoelomate animals, but the possibility of it having a true coelom has still not been completely dismissed.[14]
- Onychophora
- Tardigrada
- Arthropoda
- Chaetognatha
- Bryozoa
- Mollusca
- Annelida
- Brachiopoda
- Phoronida
- Echinodermata
- Hemichordata
- Chordata
Pseudocoelomates
In some
This fluid-filled space surrounding the internal
A pseudocoelomate or blastocoelomate is any
Important characteristics:
- lack a vascular blood system
- 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 larvalstage in some
- possibly pedomorphism
Pseudocoelomate phyla
Bilaterian pseudocoelomate phyla according to Brusca and Brusca,[12]:
- Nematoda(roundworms)
- Nematomorpha (horsehair worms)
- Loricifera
- Priapulida
- Kinorhyncha
Acoelomates
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.
- Flatworms
- Micrognathozoa
- Mesozoa[18][19]
- Xenacoelomorpha[20][21]
- Gastrotricha, traditionally viewed as blastocoelomates
- Entoprocta, traditionally viewed as blastocoelomates
- Gnathostomulida, traditionally viewed as blastocoelomates
- Cycliophora[22]
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
- ^ "celom". Merriam-Webster.com Dictionary.
- ^ "coelom" – via The Free Dictionary.
- OCLC 461974285.
- ^ Bailly, Anatole. "Greek-french dictionary online". www.tabularium.be. Retrieved 2018-01-14.
- ^ Chisholm, Hugh, ed. (1911). . Encyclopædia Britannica. Vol. 6 (11th ed.). Cambridge University Press. p. 642.
- ^ S2CID 24929317.
- ^ "Origins and Evolution of Animals". Archived from the original on 2018-11-12.
- ^ "McGraw-Hill Dictionary of Scientific and Technical Terms". Answers.com. Archived from the original on 2014-12-20.
- ISBN 978-81-315-0104-7.)
{{cite book}}: CS1 maint: multiple names: authors list (link - ISBN 978-0-03-030504-7.
- ^ Nielsen, C. (2010). "The 'new phylogeny'. What is new about it?" Palaeodiversity 3, 149–150.
- ^ ISBN 0-87893-097-3.
- ^ Nemertea
- ^ Coelom development in the priapulid worm Priapulus caudatus
- ISBN 0-534-46224-3.
- ^ Phylogeny of Syndermata (syn. Rotifera): Mitochondrial gene order verifies epizoic Seisonidea as sister to endoparasitic Acanthocephala within monophyletic Hemirotifera
- ^ Study of Rotifers of Safari Zoo Lake Lahore in Relation to Physico-chemical Parameters
- ^ Biology of Non-chordates
- ^ Comparative genomic studies on Dicyema japonicum: the phylogenetic position of dicyemids and the genomic adaptations to parasitic lifestyle
- ^ Xenoturbella bocki exhibits direct development with similarities to Acoelomorpha
- ^ Xenacoelomorph-Specific Hox Peptides: Insights into the Phylogeny of Acoels, Nemertodermatids, and Xenoturbellids
- ^ R.C.Brusca, G.J.Brusca 2003, p. 379.
Further reading
- Dudek, Ronald W.; Fix, James D. (2004). "Body Cavities". Embryology. Lippincott Williams & Wilkins. ISBN 978-0-7817-5726-3.
- Hall, B.K.; et al. (2008). "Animals Based on Three Germ Layers and a Coelem". Strickberger's evolution: the integration of genes, organisms and populations. Jones & Bartlett Learning. ISBN 978-0-7637-0066-9.
- Overhill, Raith, ed. (2006). "What are the advantages of the coelem and metamarism?". An introduction to the invertebrates (2nd ed.). Cambridge University Press. ISBN 978-0-521-85736-9.
