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Topic: Bilateria

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	Bilateria - Wikipedia, the free encyclopedia
		The Bilateria, having bilateral symmetry, are a subregnum (a major group) of animals, including the majority of phyla; the most notable exceptions are the sponges and cnidarians.
		For the most part, Bilateria have bodies that develop from three different germ layers, called the endoderm, mesoderm, and ectoderm.
		Most Bilateria also have an internal body cavity, called a coelom when it lies within the mesoderm, and a pseudocoelom otherwise.
	en.wikipedia.org /wiki/Bilateria (279 words)

	Bilateria
		The Bilateria are those animals which have a body composed of three different germ layers, called the endoderm[?], mesoderm, and ectoderm[?].
		Basically, the Bilateria include all animals that are (more or less) bilaterally symmetrical and, except for a few flatworms, have an internal body cavity (coelom or pseudocoelom) with a mouth at one end and an anus at the other.
		The two divisions of the Bilateria are Deuterostomes (echinoderms, chordates, hemichordates, Chaetognatha and Vetulicolia) and Protostomes (arthropods, annelid worms, molluscs and many more groups).
	www.ebroadcast.com.au /lookup/encyclopedia/bi/Bilateria.html (175 words)

	Bilateria (Site not responding. Last check: 2007-10-21)
		Metazoans are divided into two basic groups: Radiata (organisms with radial symmetry, including jellyfish and their relatives) and Bilateria (organisms with twofold symmetry that gives them definite front and rear, and left and right, body surfaces).
		Whereas Radiata develop from two embryonic tissue layers (an inner endoderm and outer ectoderm), the Bilateria have a third tissue layer, the mesoderm, between the endo- and ectoderm.
		Most bilaterians also show cephalization: the evolutionary trend toward the concentration of sensory structures (such as the mouth, nerves, etc.) at the anterior end of the body -- the end of a moving animal that is usually first to encounter food, danger, or other stimuli.
	www.sciencemag.org /feature/data/tol/bilateria.html (159 words)

	Bilateria -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-21)
		The most notable exception is the (Marine invertebrates with tube feet and calcite-covered five-part radially symmetrical bodies) echinoderms, which are radially symmetrical as adults, but are bilaterally symmetrical as larvae.
		Most Bilateria also have an internal body cavity, called a (A cavity in the mesoderm of an embryo that gives rise in humans to the pleural cavity and pericardial cavity and peritoneal cavity) coelom when it lies within the mesoderm, and a (Click link for more info and facts about pseudocoelom) pseudocoelom otherwise.
		It was previously thought that acoelomates gave rise to the other group, but it now appears that in the main acoelomate phyla ((Parasitic or free-living worms having a flattened body) flatworms and (Click link for more info and facts about gastrotrich) gastrotrichs) the absence is secondary.
	www.absoluteastronomy.com /encyclopedia/B/Bi/Bilateria.htm (293 words)

	Rieger (1986): Origin of Bilateria (Site not responding. Last check: 2007-10-21)
		On the other hand, with an acoelomate stem form, fiber-form muscle cells analogous to those of recent turbellarians would be the original form, and a myoepithelial organization of the musculature would have had to have arisen secondarily in individual coelomate groups.
		The consequences of such an interpretation are (1) the plesiomorphy of myoepithelial musculature in adult bilaterians and (2) a sister-group relationship of Bilateria and Cnidaria.
		Rather, these two extremes of body form are special adaptations in the course of ontogeny: acoelomate or pseudocoelomate in the case of millimeter-sized larvae and juveniles moving by cilia, coelomate in the case of centimeter- to decimeter-sized adult forms.
	www.umesci.maine.edu /biology/labs/origin (3987 words)

	Archived Data for Collins 98: Bilateria (Site not responding. Last check: 2007-10-21)
		Collins, A. Evaluating multiple alternative hypotheses for the origin of Bilateria: An analysis of 18S rRNA molecular evidence.
		Bilateria is not likely to be the sister group of Radiata or Ctenophora, nor is it likely that Bilateria gave rise to Cnidaria or Ctenophora.
		The endomesodermal muscles of bilaterians may be homologous to the endodermal muscles of cnidarians, implying that the original bilaterian mesodermal muscles were myoepithelial.
	www.ucmp.berkeley.edu /archdata/Collins98/bilateria.html (333 words)

	Animal - Wikipedia, the free encyclopedia (Site not responding. Last check: 2007-10-21)
		There are exceptions to each of these characteristics, however - for instance adult echinoderms are radially symmetric, and certain parasitic worms have extremely simplified body structures.
		The Myxozoa, single-celled parasites that were originally considered Protozoa, are now believed to have developed from the Bilateria as well.
		These were originally considered some of the most primitive Bilateria, but it now appears they developed from more complex ancestors.
	www.secaucus.us /project/wikipedia/index.php/Animal (1800 words)

	The origins of axial patterning in the metazoa: how old is bilateral symmetry? (Site not responding. Last check: 2007-10-21)
		ABSTRACT Bilateral symmetry is a hallmark of the Bilateria.
		It is achieved by the intersection of two orthogonal axes of polarity: the anterior-posterior (A-P) axis and the dorsal-ventral (D-V) axis.
		It is widely thought that bilateral symmetry evolved in the common ancestor of the Bilateria.
	www.ijdb.ehu.es /abstract.03078/a523.htm (199 words)

	Learn more about Animal in the online encyclopedia. (Site not responding. Last check: 2007-10-21)
		The Myxozoa, a group of microscopic parasites, have been considered reduced cnidarians but may instead be derived from the Bilateria.
		The remaining forms comprise a group called the Bilateria, since they are bilaterally symmetric (at least to some degree), and are triploblastic.
		The blastula invaginates without filling in first, so the endoderm is simply its inner lining, and the interior then fills in to become a third layer (mesoderm) between the others.
	www.onlineencyclopedia.org /a/an/animal.html (1497 words)

	Hox and Rocks
		The old view was that the Bilateria also started simple and gained complexity over the course of hundreds of millions of years.
		These are all branches just in the Bilateria, animals that display bilateral symmetry during their life.Each level down describes animals that are simpler, with less complex body morphologies and more similarities to non-Bilaterians.
		Obviously a major difference between a radially symmetrical organism and a bilateral one is the possession of a head and a tail.
	radio.weblogs.com /0100187/gems/NEWSLETTER/hox.html (1969 words)

	FOSSILS, MOLECULAR CLOCKS AND THE CAMBRIAN EXPLOSION (Site not responding. Last check: 2007-10-21)
		Recent inquiries into the relationships among the animal phyla have demonstrated that Bilateria can be subdivided into two groups, the protostomes and the deuterostomes, the latest common ancestor of which is referred to as PDA (Protostome-Deuterostome Ancestor).
		However, all molecular clock analyses estimate that PDA is minimally 100 Ma older, and most analyses estimate that it is 300-500 Ma older, than the first appearance of bilaterians in the fossil record.
		Analyzing the concatenated sequence from three different proteins (900 amino acids) from seven taxa (demosponge, polychaete and five echinoderms) and three calibration points we find that the minimum age of PDA is 540 Ma ago, and the minimum age of crown-group Metazoa is just over 600 Ma ago.
	gsa.confex.com /gsa/2001AM/finalprogram/abstract_26837.htm (425 words)

	Survey of the Animal Kingdom (Site not responding. Last check: 2007-10-21)
		Bilateria breaks into 3 groups: Grade Coelomata (pronounced "Seelomata"), Grade Pseudocoelomata, and Grade Acoelomata.
		The anatomical structures of all the organisms is Branch Bilateria come from three layers of cells during development:
		They have bilateral symmetry so they are in Branch Bilateria, they have body cavities not lined with mesodermal tissue so they are in Grade Pseudocoelamata.
	www.bio200.buffalo.edu /labs/SAK.html (495 words)

	Palaeos Invertebrates: Bilateria
		The Bilateria are sometimes divided into three groups or grades: Grade Acoelomata, Grade Pseudocoelomata, and Grade Coelomata (note that the correct pronunciation "Seelomata").
		The following diagram [1] lists 18S ribosomal RNA mutations, which indicates not only the distinctness of the Bilateria, but also the close relationship between the coelomate phyla, indicating that they all evolved from a common ancestor within a very short time (confirmation of the existence of the so-called "Cambrian explosion").
		A series of new discoveries challenge this view and raise the possibility that the whole cluster with numerous genes appeared in a single genetic radiation and that the history of the cluster since has been dominated by gene divergence and extinction.
	www.palaeos.com /Invertebrates/Bilateria.htm (1270 words)

	Rieger (1986): Footnotes (Site not responding. Last check: 2007-10-21)
		According to these concepts, planktonic organisms, similar to the larvae of the Protostomia or Deuterostomia and which are transformed into adult benthic vermiform organisms, stand at the base of the Bilateria.
		The "ectomesodermal" part of tissue, which concerns the structuring of tissue between the epidermis and intestine to various extents in many bilaterians (e.g., the spiralians), I distinguish here as "ectomesenchyme" and, in reference to Salvini-Plawen & Splechtna (1978) and Salvini-Plawen (1982), equate it with ectomesenchymal tissue of coelenterates.
		On this point, it should be noted that the body cavity of almost all larval forms of the Bilateria corresponds in large part to Hyman's (1951) definition of a pseudocoel.
	www.umesci.maine.edu /biology/labs/origin/coelfoot.htm (595 words)

	New developments concerning the evolutionary tree of animals. A clue to the Cambrian explosion
		The origin of animals with a very simple structure, such as sponges, jellyfish and sea anemones — ancient species, which are at the root of the genealogical tree of animals —; has been clearly identified.
		The hypothesis of a complex ancestor of Bilateria could provide an answer to the question of the "Cambrian explosion", the sudden appearance, 540 million years ago, in the Cambrian period, of almost all the modern bilateral phyla.
		According to researchers, the extraordinary diversification of organizational plans was made possible, in the right ecological conditions, by the existence, in these ancestors, of complex networks of genes which regulate development.
	www.cnrs.fr /cw/en/pres/compress/mist250699.html (762 words)

	Eumetazoa - Wikispecies
		Superphylum: Radiata - Bilateria: Protostomia - Bilateria: Deuterostomia
		Alternative Superphylum: Radiata - Bilateria: Deuterostomia - Lophotrochozoa/Spiralia - Platyzoa/Spiralia - Ecdysozoa
		Bilateria are bilaterally symmetric animals and have three germ layers, like humans or worms.
	species.wikipedia.org /wiki/Eumetazoa (138 words)

	Conservation of Brachyury, Mef2, and Snail in the myogenic lineage of jellyfish: a connection to the mesoderm of ... (Site not responding. Last check: 2007-10-21)
		Conservation of Brachyury, Mef2, and Snail in the myogenic lineage of jellyfish: a connection to the mesoderm of bilateria.
		Conservation of Brachyury, Mef2, and Snail in the myogenic lineage of jellyfish: a connection to the mesoderm of bilateria.The terms diploblasts and triploblasts are therefore, often used to group prebilaterian and bilaterian animals, respectively.
		We investigated the hypothesis, that the entocodon could be homologous to the third germ layer of bilaterians by analyzing the structures and expression patterns of the homologues of Brachyury, Mef2, and Snail in the jellyfish Podocoryne carnea.
	www.pdg.cnb.uam.es /UniPub/iHOP/gp/9203400.html (233 words)

	Bilateria - Wikipédia
		Em zoologia, chama-se Bilateria a um clade que inclui os animais do sub-reino Metazoa que apresentam simetria bilateral, em contraposição com os Radiata, que têm simetria radial).
		Geralmente há uma cavidade ao redor do intestino, chamada celoma, surgindo como uma divisão da mesoderme, ou ao menos uma versão reduzida disso - o pseudoceloma - onde a divisão ocorre entre a mesoderme e a endoderme, fenómeno comum em formas microscópicas.
		Fazem parte deste grupo, todos os metazoários, com exceção dos Cnidaria e dos Ctenophora (águas vivas, anémonas, corais, etc); os Myxozoa, um grupo de parasitas microscópicos por vezes incluídos nos Radiata, têm sido considerados cnidários reduzidos, porém, podendo ser derivados dos Bilateria.
	pt.wikipedia.org /wiki/Bilateria (298 words)

	Pharyngula (Site not responding. Last check: 2007-10-21)
		Together, these sets of genes establish the front-back and top-bottom axes of the animal, which in turn establishes bilaterality—this specifically laid out three-dimensional organization is a hallmark of the lineage Bilateria, to which we and 99% of all the other modern animal species belong.
		There are some animals that don't belong to the Bilateria, though: members of the phylum Cnidaria, the jellyfish, hydra, sea anemones, and corals, which are typically radially symmetric.
		That some members of the Cnidaria exhibit precisely the same molecular organization to their body plan suggests that the function for these molecules arose early in the origin of multicellular animals, and that the radially symmetrical cnidarians have secondarily lost them.
	pharyngula.org /index/bilateral_symmetry_in_a_sea_anemone (872 words)

	The last common bilaterian ancestor -- Erwin and Davidson 129 (13): 3021 -- Development
		of the Bilateria predates the PDA, as illustrated in Fig.
		Holland, L. Z., Kene, M., Williams, N. and Holland, N. Sequence and embryonic expression of the amphioxus engrailed gene (AmphiEn): the metameric pattern of transcription resemples that of its segment-polarity homolog in Drosophila.
		Holland, L. Body-plan evolution in the Bilateria: early antero-posterior patterning and the deuterostome-protostome dichotomy.
	dev.biologists.org /cgi/content/full/129/13/3021 (7483 words)

	Bilateria - Wikipedia
		Zu den Bilateria gehören alle spiegelsymmetrischen (spiegelbildlich gebauten) vielzelligen Stämme sowie die von solchen Tieren abstammenden Stämme (beispielsweise Stachelhäuter).
		Im Gegensatz zu den Bilateria sind die Hohltiere primär radiärsymmetrisch gebaut.
		Aufgrund des Spermienaufbaus sowie der Organisation der Muskelzellen werden die Bilateria in der Phylogenetik mit den Rippenquallen (Ctenophora) als Taxon Acrosomata zusammengefasst.
	de.wikipedia.org /wiki/Bilateria (129 words)

	Bilateria
		Bilateria: Most animals exhibit bilateral symmetry and are triploblastic
		Most of the diversity of animals is found in 2 big lineages of Bilateria (604-606)
		Bilateria can have a cavity for organs between gut and body wall, but many
	www.sci.sdsu.edu /classes/bio201/Flatworms.html (358 words)

	Shankland.abs
		We suggest that this head/trunk distinction is a synapomorphy of the Bilateria as a whole, and that it reflects some sort of regional or temporal distinction within the body plan of an early bilaterian ancestor.
		A model will be discussed in which the bilaterian body plan is derived from a radically organized prebilaterian ancestor by the addition of a discrete 'trunk domain' that was situated anisotropically with respect to the axis of radial symmetry.
		If this is the case, then AP organization would have been secondarily imposed onto the bilaterian head domain by its functional integration with the elongating trunk domain.
	www.mbl.edu /CASSLS/Shankland.abs.html (290 words)

	Palaeos Invertebrates: Metazoa (Site not responding. Last check: 2007-10-21)
		"Procoelomates": sometimes bizarre worms near the root of the Bilateria.
		In addition to a more complex inside-outside pattern of tissues and the ancestral front-to-back organization, Bilateria have a separate top and bottom.
		There are three groups of Bilateria which show some internal cohesion.
	www.palaeos.com /Invertebrates (1516 words)

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