Which Of The Following Statements About Bilaterian Animals Is False?

The primary body crenel in most animals

Coelom
Cross-department of an oligochaete worm. The worm's body cavity surrounds the central typhlosole.
Details
Pronunciation	( Come across-ləm, plural coeloms or coelomata meet-LOH-mə-tə)
Identifiers
Greek	koilōma
Anatomical terminology [edit on Wikidata]

The coelom (or celom)^[ane] is the chief body crenel in about animals^[ii] and is positioned inside the torso 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 applied purposes, coelom characteristics have been used to classify bilaterian animal phyla into informal groups.

Etymology [edit]

The term coelom derives from the Ancient Greek word κοιλία ( koilía ), significant 'cavity'.^{[3] [iv] [five]}

Construction [edit]

Development [edit]

The coelom is the mesodermally lined crenel betwixt the gut and the outer trunk wall.

During the development of the embryo, coelom germination begins in the gastrulation phase. The developing digestive tube of an embryo forms as a blind pouch chosen the archenteron.

In Protostomes, the coelom forms past a process known every bit schizocoely.^[six] The archenteron initially forms, and the mesoderm splits into 2 layers: the first attaches to the torso 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 torso crenel.

In Deuterostomes, the coelom forms by enterocoely.^[6] 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 (vertebrates, tunicates, and lancelets), echinoderms (starfish, body of water urchins, body of water cucumbers), and hemichordates (acorn worms and graptolites).

Origins [edit]

The evolutionary origin of the coelom is uncertain. The oldest known animal to have had a body crenel was the Vernanimalcula. Electric current hypothesis include:^{[ citation needed ] [7]}

• The acoelomate theory, which states that coelom evolved from an acoelomate antecedent.
• The enterocoel theory, which states that coelom evolved from gastric pouches of cnidarian ancestors. This is supported by research on flatworms^{[ commendation needed ]} and small worms recently discovered^{[ description needed ]} in marine brute^{[ citation needed ]} ("coelom"^[8]).

Functions [edit]

A coelom can absorb shock or provide a hydrostatic skeleton. It tin too back up an immune system in the class of coelomocytes that may either be attached to the wall of the coelom or may float virtually in information technology freely. The coelom allows muscles to abound independently of the body wall — this feature can be seen in the digestive tract of tardigrades (water bears) which is suspended within the torso in the mesentery derived from a mesoderm-lined coelom.

Coelomic fluid [edit]

The fluid within the coelom is known equally coelomic fluid. This is circulated by mesothelial cilia or by contraction of muscles in the body wall which are themselves of mesin.^{[ description needed ] [nine]} The coelomic fluid serves several functions: information technology acts as a hydroskeleton; it allows complimentary move and growth of internal organs; it serves for ship of gases, nutrients and waste material products around the body; it allows storage of sperm and eggs during maturation; and it acts as a reservoir for waste product.^[10]

Classification in zoology [edit]

In the by, some zoologists grouped bilaterian animal phyla based on characteristics related to the coelom for practical purposes, knowing, and explicitly stating, that these groups were non phylogenetically related. Animals were classified in three informal groups according to the type of torso cavity they possess, in a non-taxonomic, utilitarian manner, as the Acoelomata, Pseudocoelomata, and Coelomata. These groups were never intended to represent related animals, or a sequence of evolutionary traits.

All the same, although this scheme was followed by a number of college textbooks and some general classifications, information technology is at present about totally abandoned as a formal classification. Indeed, as late as 2010, 1 author of a molecular phylogeny study mistakenly chosen this classification scheme the "traditional, morphology-based phylogeny".^[xi]

Nomenclature 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 consummate lining called peritoneum derived from mesoderm (i of the three principal tissue layers). The complete mesoderm lining allows organs to be attached to each other so that they tin can exist suspended in a item lodge while even so being able to move freely inside the crenel. About bilateral animals, including all the vertebrates, are coelomates.

Pseudocoelomate animals have a pseudocoelom (literally "false crenel"), which is a fluid filled body crenel. 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 equally in a coelomate. All pseudocoelomates are protostomes; however, non all protostomes are pseudocoelomates. An case of a Pseudocoelomate is the roundworm. Pseudocoelomate animals are also referred to as Blastocoelomate.

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

Coelomates [edit]

Coeloms developed in triploblasts just were subsequently lost in several lineages. The lack of a coelom is correlated with a reduction in torso size. Coelom is sometimes incorrectly used to refer to any developed digestive tract. Some organisms may non possess a coelom or may have a false coelom (pseudocoelom). Animals having coeloms are called coelomates, and those without are chosen acoelomates. There are also subtypes of coelom:^{[ citation needed ]}

• schizocoelom: develops from divide in mesoderm establish in annelids, arthropods and molluscs
• haemocoelom: true coelom reduced and crenel filled with claret plant from arthropoda to mollusca
• enterocoelom: develops from wall of embryonic gut found from echinodermata to chordata

Coelomate phyla [edit]

According to Brusca and Brusca,^[12] the post-obit bilaterian phyla possess a coelom:

• Nemertea, traditionally viewed as acoelomates
• Priapulida
• Annelida
• Onychophora
• Tardigrada
• Arthropoda
• Mollusca
• Phoronida
• Ectoprocta
• Brachiopoda
• Echinodermata
• Chaetognatha
• Hemichordata
• Chordata

Pseudocoelomates [edit]

In some protostomes, the embryonic blastocoele persists as a trunk cavity. These protostomes have a fluid filled main body crenel 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 pseudocoelomate or blastocoelomate is any invertebrate creature with a 3-layered body and a pseudocoel. The coelom was apparently lost or reduced every bit a upshot of mutations in sure types of genes that affected early development. Thus, pseudocoelomates evolved from coelomates.^[xiii] "Pseudocoelomate" is no longer considered a valid taxonomic group, since it is not monophyletic. Nevertheless, information technology is even so used every bit a descriptive term.

Important characteristics:

• lack a vascular claret system
  • diffusion and osmosis circulate nutrients and waste products throughout the body.
• lack a skeleton
  • hydrostatic pressure level gives the trunk a supportive framework that acts equally a skeleton.
• no partition
• body wall
  • epidermis and muscle
  • frequently syncytial
  • normally 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

Pseudocoelomate phyla [edit]

Co-ordinate to Brusca and Brusca,^[12] bilaterian pseudocoelomate phyla include:

• Rotifera
• Kinorhyncha
• Nematoda
• Nematomorpha
• Acanthocephala
• Loricifera

Some authors listing the following phyla as pseudocoelomates:^{[ citation needed ]}

Ecdysozoan pseudocoelomates

• Nematoda (roundworms)
• Nematomorpha (nematomorphs or horsehair worms)
• Loricifera
• Priapulida
• Kinorhyncha

Spiralian pseudocoelomates

• Gastrotricha
• Entoprocta
• Rotifera (rotifers)
• Acanthocephala (spiny-headed worms)

Acoelomates [edit]

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 volition compress. Therefore, acoelomate organs are not protected from crushing forces practical to the beast's outer surface. The coelom tin can exist used for diffusion of gases and metabolites etc. These creatures do not have this need, equally the surface expanse to volume ratio is large enough to permit absorption of nutrients and gas exchange past improvidence lone, due to dorso-ventral flattening.

• Platyhelminthes
• Gastrotricha, traditionally viewed equally blastocoelomates
• Entoprocta, traditionally viewed equally blastocoelomates
• Gnathostomulida, traditionally viewed as blastocoelomates
• Cycliophora^[14]

According to others, acoelomates include the cnidarians (jellyfish and allies), and the ctenophores (comb jellies), platyhelminthes (flatworms including tapeworms, etc.), Nemertea, and Gastrotricha.^{[ citation needed ]}

• [1]*

See also [edit]

• Intestinal crenel

References [edit]

1. ^ "celom". Merriam-Webster Dictionary.
2. ^ "coelom" – via The Free Dictionary.
3. ^ Bailly, Anatole (1981-01-01). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN2010035283. OCLC 461974285.
4. ^ Bailly, Anatole. "Greek-french dictionary online". www.tabularium.exist . Retrieved 2018-01-14 .
5. ^ Chisholm, Hugh, ed. (1911). "Coelom and Serous Membranes". Encyclopædia Britannica. Vol. six (11th ed.). Cambridge Academy Press. p. 642.
6. ^ ^{a b} Lüter, Carsten (2000-06-01). "The origin of the coelom in Brachiopoda and its phylogenetic significance". Zoomorphology. 120 (1): 15–28. doi:x.1007/s004359900019. ISSN 1432-234X. S2CID 24929317.
7. ^ "Origins and Development 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.; Play tricks, Richard, Southward.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 205. ISBN978-81-315-0104-7.
10. ^ Dorit, R. 50.; Walker, Westward. F.; Barnes, R. D. (1991). Zoology . Saunders College Publishing. p. 190. ISBN978-0-03-030504-7.
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. ^ Evers, Christine A., Lisa Starr. Biology:Concepts and Applications. 6th ed. United States:Thomson, 2006. ISBN 0-534-46224-3.
14. ^ R.C.Brusca, G.J.Brusca 2003, p. 379.

Farther reading [edit]

• Dudek, Ronald West.; Prepare, James D. (2004). "Body Cavities". Embryology. Lippincott Williams & Wilkins. ISBN978-0-7817-5726-3.
• Hall, B.1000.; 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. ISBN978-0-7637-0066-9.
• Overhill, Raith, ed. (2006). "What are the advantages of the coelem and metamarism?". An introduction to the invertebrates (2nd ed.). Cambridge Academy Press. ISBN978-0-521-85736-nine.

Source: https://en.wikipedia.org/wiki/Coelom

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