Deuterostomes (taxonomic term: Deuterostomia; from the Greek: "second mouth") are a superphylum of animals Animals are a major group of mostly multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and independently. All animals are also. They are a subtaxon A taxon is a group of (one or more) organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a taxonomic group is done by a taxonomist. It is not uncommon for one taxonomist to disagree with another on what exactly belongs to of the Bilateria The bilateria are all animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside. Radially symmetrical animals like jellyfish have a topside and downside, but no front and back. The bilateralia are a subregnum (a major group) of animals, including the majority of phyla; the most notable exceptions branch of the subregnum Eumetazoa Eumetazoa is a clade comprising all major animal groups except sponges, placozoa and several other little known animals. Characteristics of eumetazoans include true tissues organized into germ layers, and an embryo that goes through a gastrula stage. The clade is usually held to contain at least Ctenophora, Cnidaria, and Bilateria. Whether, and are opposed to the protostomes Protostomia are a clade of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development. Deuterostomes are distinguished by their embryonic development Embryogenesis is the process by which the embryo is formed and develops. It starts with the fertilization of the ovum (or egg) which, after fertilization, is referred to as a zygote. The zygote undergoes rapid mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of an; in deuterostomes, the first opening (the blastopore A blastopore is an opening into the archenteron during the embryonic stages of an organism. The distinction between protostomes and deuterostomes is based on the direction in which the mouth develops in relation to the blastopore. Protostome derives from the Greek word protostoma meaning "first mouth"(πρώτος + στόμα) whereas) becomes the anus, while in protostomes it becomes the mouth The mouth is the first portion of the alimentary canal that receives food and begins digestion by mechanically breaking up the solid food particles into smaller pieces and mixing them with saliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth. Deuterostomes are also known as enterocoelomates because their coelom The coelom is a fluid filled cavity formed within the mesoderm. Coeloms developed in triploblasts but were subsequently lost in several lineages. Loss of coelom is correlated with reduction in body size. Coeloms are only ever present in triploblastic animals, though coelom is sometimes (incorrectly) used to refer to any developed digestive tract develops through enterocoely.

There are four extant phyla of deuterostomes:

The phylum Chaetognatha Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic and can attach to algae or rocks. They are found in all marine waters from surface tropical waters and shallow tide pools to the deep sea and polar (arrow worms) may also belong here. Extinct groups may include the phylum Vetulicolia. Echinodermata, Hemichordata and Xenoturbellida form the clade Ambulacraria.[1]

In both deuterostomes and protostomes, a zygote first develops into a hollow ball of cells, called a blastula The blastula (from Greek βλαστός , meaning "sprout") is an early stage of embryonic development in animals. It is also called blastosphere. It is produced by cleavage of a fertilized ovum and consists of a spherical layer of around 128 cells with a large fluid filled space called the blastocoel in the animal pole of the embryo. In deuterostomes, the early divisions occur parallel or perpendicular to the polar axis. This is called radial cleavage, and also occurs in certain protostomes, such as the lophophorates. Most deuterostomes display indeterminate cleavage, in which the developmental fate of the cells in the developing embryo are not determined by the identity of the parent cell. Thus if the first four cells are separated, each cell is capable of forming a complete small larva, and if a cell is removed from the blastula the other cells will compensate.

In deuterostomes the mesoderm A germ layer, occasionally referred to as a germinal epithelium, is a group of cells, formed during animal embryogenesis. Germ layers are particularly pronounced in the vertebrates; however, all animals more complex than sponges produce two or three primary tissue layers (sometimes called primary germ layers). Animals with radial symmetry, like forms as evaginations of the developed gut that pinch off, forming the coelom By the broadest definition, a body cavity is any fluid filled space in a multicellular organism. However, the term usually refers to the space, located between an animal’s outer covering and the outer lining of the gut cavity, where internal organs develop. "The body cavity" of the human body cavities normally refers to the ventral. This is called enterocoely.

Both the Hemichordata and Chordata have gill slits, and primitive fossil echinoderms also show signs of gill slits. A hollow nerve cord is found in all chordates, including tunicates Tunicates, also known as urochordates, are members of the subphylum Tunicata or Urochordata, a group of underwater saclike filter feeders with incurrent and excurrent siphons that is classified within the phylum Chordata. While most tunicates live on the ocean floor and are commonly known as sea squirts and sea pork, others – such as salps, (in the larval stage). Some hemichordates also have a tubular nerve cord. In the early embryonic stage it looks like the hollow nerve cord of chordates. Because of the degenerated nervous system of echinoderms, it is not possible to discern much about their ancestors in this matter, but based on different facts it is quite possible that all the present deuterostomes evolved from a common ancestor that had gill slits, a hollow nerve cord and a segmented body. It could have resembled the small group of Cambrian deuterostomes named Vetulicolia.

Contents

Formation of mouth and anus

All chordates, such as birds and mammals, are deuterostomes. Shown here is a Barred Owl The Barred Owl is a large typical owl. It goes by many other names, including eight hooter, rain owl, wood owl, and striped owl, but is probably known best as the hoot owl. Main article: Embryological origins of the mouth and anus

Deuterostome means "secondary mouth", and related to the fact that after the anus forms, a secondary opening forms in deuterostome embryos that goes on to be the mouth; the gut tunnels down from the mouth to anus to connect the two.[verification needed]

Origins

The majority of animals more complex than jellyfish Jellyfish are free-swimming members of the phylum Cnidaria. Jellyfish have several different morphologies that represent several different cnidarian classes including the Scyphozoa (over 200 species), Staurozoa (about 50 species), Cubozoa (about 20 species), and Hydrozoa (about 1000–1500 species that make jellyfish and many more that do not) and other Cnidarians Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic, mostly marine, environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are are split into two groups, the protostomes Protostomia are a clade of animals. Together with the deuterostomes and a few smaller phyla, they make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development and deuterostomes, and chordates are deuterostomes.[2] It seems very likely that 555 million years old Kimberella was a member of the protostomes.[3][4] If so, this means that the protostome and deuterostome lineages must have split some time before Kimberella appeared — at least 558 million years ago, and hence well before the start of the Cambrian 542 million years ago.[2] The Ediacaran The Ediacaran Period is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon. Its status as an official geological period was ratified in 2004 by the International Union of Geological Sciences (IUGS), making it fossil Ernietta, from about 549 to 543 million years ago, may represent a deuterostome animal.[5]

Fossils of one major deuterostome group, the echinoderms Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. Aside from the problematic Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian period (whose modern members include sea stars Starfish or sea stars are echinoderms belonging to the class Asteroidea. The names "starfish" and "sea star" essentially refer to members of the Class Asteroidea. However, common usage frequently finds "starfish" and "sea star" also applied to ophiuroids which are correctly referred to as "brittle stars&, sea urchins Sea urchins or urchins are small, spiny, globular animals which, with their close kin, such as sand dollars, constitute the class Echinoidea of the echinoderm phylum. They inhabit all oceans. Their shell, or "test", is round and spiny, typically from 3 to 10 centimetres across. Common colors include black and dull shades of green, olive, and crinoids Crinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms . Crinoidea comes from the Greek word krinon, "a lily", and eidos, "form". They live both in shallow water and in depths as great as 6,000 meters.[citation needed]) are quite common from the start of the Cambrian, 542 million years ago.[6] The Mid Cambrian The Cambrian is the first geological period of the Paleozoic Era, lasting from 542 ± 0.3 million years ago to 488.3 ± 1.7 million years ago(ICS, 2004,; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the classical name for fossil Rhabdotubus johanssoni has been interpreted as a pterobranch hemichordate.[7] Opinions differ about whether the Chengjiang fauna The Maotianshan Shales area a series of lower Cambrian deposits, famous for their Konservat Lagerstätten, or high number of fossils. They take their name from Maotianshan Hill (simplified Chinese: 帽 fossil Yunnanozoon, from the earlier Cambrian, was a hemichordate or chordate.[8][9] Another Chenjiang fossil, Haikouella lanceolata, also from the Chengjiang fauna, is interpreted as a chordate and possibly a craniate, as it shows signs of a heart, arteries, gill filaments, a tail, a neural chord with a brain at the front end, and possibly eyes — although it also had short tentacles round its mouth.[9] Haikouichthys Haikouichthys is an extinct genus of craniate (creatures with backbones and distinct heads) believed to have lived c. 530 million years ago, during the Cambrian explosion. Haikouichthys had a defined skull and other characteristics that have led paleontologists to label it a true craniate, and even to be popularly characterized as one of the and Myllokunmingia Myllokunmingia is a chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high, also from the Chenjiang fauna, are regarded as fish A fish is any aquatic vertebrate animal that is covered with scales, and equipped with two sets of paired fins and several unpaired fins. Most fish are "cold-blooded", or ectothermic, allowing their body temperatures to vary as ambient temperatures change. Fish are abundant in most bodies of water. They can be found in nearly all aquatic.[10][11] Pikaia Pikaia gracilens is an extinct animal known from the Middle Cambrian Burgess Shale of British Columbia. 16 specimens of Pikaia are known from the Greater Phyllopod bed, where they comprise 0.03% of the community, discovered much earlier but from the Mid Cambrian Burgess Shale The Burgess Shale Formation — located in the Canadian Rockies of British Columbia — is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils. It is 505 million years old, one of the earliest soft-parts fossil beds, is also regarded as a primitive chordate.[12] On the other hand fossils of early chordates are very rare, since non-vertebrate chordates have no bones or teeth, and none have been reported for the rest of the Cambrian.

References

  1. ^ S. J. Bourlat, T. Juliusdottir, C. J. Lowe, R. Freeman, J. Aronowicz, M. Kirschner, E. S. Lander, M. Thorndyke, H. Nakano, A. B. Kohn, A. Heyland, L. L. Moroz, R. R. Copley, M. J. Telford (2006). "Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida". Nature 444: 85–88.
  2. ^ a b Erwin, Douglas H.; Eric H. Davidson (1 July 2002). "The last common bilaterian ancestor". Development 129 (13): 3021–3032. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 12070079. http://dev.biologists.org/cgi/content/full/129/13/3021.
  3. ^ New data on Kimberella, the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications (2007), "Fedonkin, M.A.; Simonetta, A; Ivantsov, A.Y.", in Vickers-Rich, Patricia; Komarower, Patricia, The Rise and Fall of the Ediacaran Biota, Special publications, 286, London: Geological Society, pp. 157–179, doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1144/SP286.12, ISBN The International Standard Book Number is a unique numeric commercial book identifier based upon the 9-digit Standard Book Numbering (SBN) code created by Gordon Foster, now Emeritus Professor of Statistics at Trinity College, Dublin, for the booksellers and stationers W.H. Smith and others in 1966 9781862392335, OCLC OCLC Online Computer Library Center, Inc. is "a nonprofit, membership, computer library service and research organization dedicated to the public purposes of furthering access to the world’s information and reducing information costs". It was incorporated on July 6, 1967 as the not-for-profit Ohio College Library Center. More than 72,00 191881597 156823511 191881597
  4. ^ Butterfield, N.J. (2006). "Hooking some stem-group "worms": fossil lophotrochozoans in the Burgess Shale". Bioessays 28 (12): 1161–6. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1002/bies.20507. PMID A PMID is a unique number assigned to each PubMed citation of life sciences and biomedical scientific journal articles. The related Pubmed Central archive may additionally assign a separate number, a PMCID (PubMed Central Identifier), normally written with a PMC prefix 17120226.
  5. ^ Dzik , J. (June 1999). "Organic membranous skeleton of the Precambrian metazoans from Namibia". Geology 27 (6): 519–522. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1130/0091-7613(1999)027<0519:OMSOTP>2.3.CO;2. http://geology.geoscienceworld.org/cgi/content/abstract/27/6/519. Retrieved 2008-09-22. Ernietta is from the Kuibis formation, approximate date given by Waggoner, B. (2003). "The Ediacaran Biotas in Space and Time". Integrative and Comparative Biology 43 (1): 104–113. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1093/icb/43.1.104. http://icb.oxfordjournals.org/cgi/content/full/43/1/104. Retrieved 2008-09-22.
  6. ^ Bengtson, S. (2004). Early skeletal fossils. in Lipps, J.H., and Waggoner, B.M.. "Neoproterozoic–Cambrian Biological Revolutions" (PDF). Palentological Society Papers 10: 67–78. http://www.cosmonova.org/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf. Retrieved 2008-07-18.
  7. ^ Bengtson, S., and Urbanek, A. (October 2007). "Rhabdotubus, a Middle Cambrian rhabdopleurid hemichordate". Lethaia 19 (4): 293–308. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1111/j.1502-3931.1986.tb00743.x. http://www3.interscience.wiley.com/journal/120025616/abstract. Retrieved 2008-09-23.
  8. ^ Shu, D., Zhang, X. and Chen, L. (April 1996). "Reinterpretation of Yunnanozoon as the earliest known hemichordate". Nature 380: 428–430. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1038/380428a0. http://www.nature.com/nature/journal/v380/n6573/abs/380428a0.html. Retrieved 2008-09-23.
  9. ^ a b Chen, J-Y., Hang, D-Y., and Li, C.W. (December 1999). "An early Cambrian craniate-like chordate". Nature 402: 518–522. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1038/990080. http://www.nature.com/nature/journal/v402/n6761/abs/402518a0.html. Retrieved 2008-09-23.
  10. ^ Shu, D-G., Conway Morris, S., and Han, J., et al. (January 2003). "Head and backbone of the Early Cambrian vertebrate Haikouichthys". Nature 421 (6922): 526–529. doi A digital object identifier is a character string used to uniquely identify an electronic document or other object. Metadata about the object is stored in association with the DOI name and this metadata may include a location, such as a URL, where the object can be found. The DOI for a document is permanent, whereas its location and other metadata:10.1038/nature01264. PMID 12556891. http://www.nature.com/nature/journal/v421/n6922/abs/nature01264.html. Retrieved 2008-09-21.
  11. ^ Shu, D-G., Conway Morris, S., and Zhang, X-L. (November 1999). "Lower Cambrian vertebrates from south China" (PDF). Nature 402: 42. doi:10.1038/46965. http://www.bios.niu.edu/davis/bios458/Shu1.pdf. Retrieved 2008-09-23.
  12. ^ Shu, D-G., Conway Morris, S., and Zhang, X-L. (November 1996). "A Pikaia-like chordate from the Lower Cambrian of China". Nature 384: 157–158. doi:10.1038/384157a0. http://www.nature.com/nature/journal/v384/n6605/abs/384157a0.html. Retrieved 2008-09-23.

External links

Wikispecies has information related to: Deuterostomia
Extant phyla of kingdom Animalia by subkingdom
Parazoa Porifera (Calcarea, Demospongiae, Hexactinellida) · Placozoa (Trichoplax)
Mesozoa Orthonectida · Rhombozoa
Eumetazoa
Radiata Ctenophora · Cnidaria (Anthozoa, Hydrozoa, Scyphozoa, Cubozoa, Staurozoa, Myxozoa)
Bilateria
Protostomia
Ecdysozoa

Cycloneuralia: Scalidophora (Kinorhyncha, Loricifera, Priapulida) · Nematoida (Nematoda, Nematomorpha)

Panarthropoda: Onychophora · Tardigrada · Arthropoda
Spiralia
Platyzoa

Platyhelminthes · Gastrotricha

Gnathifera: Rotifera · Acanthocephala · Gnathostomulida · Micrognathozoa · Cycliophora
Lophotrochozoa Trochozoa (Sipuncula, Nemertea, Mollusca, Annelida) Lophophorata (Bryozoa, Entoprocta, Phoronida, Brachiopoda)
Deuterostomia
Ambulacraria Hemichordata · Echinodermata · Xenoturbellida
Chordata Craniata (Vertebrata, Myxini) · Cephalochordata · Tunicata
Basal/disputed Acoelomorpha (Acoela, Nemertodermatida) · Chaetognatha

Categories: Animals

 

The above information uses material from Wikipedia and is licensed under the GNU Free Documentation License.
Some facts may not have been fully verified for accuracy. [Disclaimers]
This page was last archived by our server on Fri Jul 30 19:29:49 2010. [ refresh local cache ]
Displaying this page or its contents does not use any Wikimedia Foundation's resources.
The owners of this site proudly support the Wikimedia Foundation.

[Hide]▼
[Hide]▲