How To Use Metazoa In A Sentence
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The typical embryonic form of the metazoa, as it is presented for a time by this simple structure of the two-layered body, is called the gastrula; it is to be conceived as the hereditary reproduction of some primitive common ancestor of the metazoa, which we call the gastraea.
The Evolution of Man — Volume 1
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To understand the origins of complexity in metazoan body plans, then, we must find where these tissues came from; that is, how epithelia and mesenchyme arose.
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On the basis of this information it has been proposed that the earliest metazoans were probably wormlike organisms, similar to the larvae of modern cnidarians and developed from flagellate protists.
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One widely-mooted suggestion is that planktotrophic larvae, typified by the annelidan trochophore and echinoid pluteus, existed long before the metazoan radiations evident in the Cambrian fossil record.
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Surprisingly complex T-box gene complement in diploblastic metazoans
As Expected
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The ancestral metazoan gene structure gives the most parsimonious derivation of its descendant genes.
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These genetic techniques will clarify the evolutionary and phylogenetic importance of segmentation in metazoan evolution.
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The ovum is now what has been called a gastrula; and it is of importance to observe that probably all the Metazoa pass through this stage.
Darwin, and After Darwin (Vol. 1 and 3, of 3) An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions
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Fossils of the Twitya Formation are generally presumed to be cnidarians, or at least metazoans of cnidarian grade.
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They are just the simplest, barest kind of metazoan we can find now.
Mysterious Trichoplax - The Panda's Thumb
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But even if in such cases it does not occur -- i.e. if failure to detect its occurrence be not due merely to still remaining imperfections of our histological methods, -- the large number of cases in which it has been seen to occur in the formation of sundry tissues are of themselves sufficient to indicate some important difference between cells derived from ova (metazoal), and cells which have not been so derived (protozoal).
Darwin, and After Darwin (Vol. 1 and 3, of 3) An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions
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The main assumption was that the neural or blastoporal surface must be homologous throughout the Metazoa, though it was dorsal in the Chordata, ventral in the Annelida and Arthropoda.
Form and Function A Contribution to the History of Animal Morphology
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This marine worm, first described in 1949 as an acoel flatworm and later claimed as either an early metazoan offshoot or a primitive deuterostome, has recently been affiliated with primitive bivalve molluscs, based upon a study of gamete development oogenesis and an analysis of sequence data from both 18S rRNA and mitochondrial genes.
Strange worm, Xenoturbella - The Panda's Thumb
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We shall make use of it later on for our monophyletic theory of descent -- the hypothesis of a common descent of man and all the metazoa from the gastraea.
The Evolution of Man — Volume 1
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Current revision as of 06: 20, 8 February 2010 taxonomic Kingdom Animalia (also called Metazoa heterotrophs (i.e. they rely directly or indirectly on other organisms for their nourishment).
Conservapedia - Recent changes [en]
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If I were a FLID supporter, I would propose that the homeobox regulatory mechanism for body regions was a "front-loaded design element" that, once it was in place, could be modified extensively via standard evolutionary mechanisms to produce the various metameric metazoan bauplans.
Ancient Predator Revealed!
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As far as we are aware, this unusual structural organization is unique among higher metazoans, although interesting comparisons can be made with the multipartite mitochondrial genome organizations of plants and fungi.
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In the context of this thread, the homeobox regulatory mechanism of non-metameric ancestral metazoans (such as flatworms) would qualify as an exaptation for the homeobox regulatory mechanism of their metameric descendants.
Ancient Predator Revealed!
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Of course, above the level of the domains, Woese's thinking is (more or less) conventional evolution — the vertical descent of familiar monophyletic groups (the eukaryotes, the Metazoa, etc).
A Disclaimer for Behe?
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They remain the most mysterious parts of metazoan history.
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I then would run my ancestry lines from Chordata (3) down to Metazoa (2) and from Metazoa to the ground line (1).
A Disclaimer for Behe?
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I think this is very subjective; I was quite happy with Merriam Webster's definition of "metazoan," for example.
Languagehat.com: COELOM.
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Dashed lines represent an amalgam of three conservative estimates of the inferred metazoan phylogeny.
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For example, most metazoans go through a developmental stage called a gastrula - a ball of cells with an infolding that later forms the gut.
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The natural occurrence of ethanol within ripe and fermenting fruit suggests that low-level ethanol exposure via dietary ingestion is characteristic of all frugivorous metazoans.
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Li and Ding interpreted such structures as metazoan trace fossils.
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Proof of such genes would require complete genome sequences of representatives from each of the basal metazoan phyla.
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Extrapolating from these studies and from comparisons of the morphology of epithelia in lower metazoans, I propose how epithelia arose in the stem metazoan.
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The album, "Metazoa," was recorded with and produced by Billy Anderson (NEUROSIS, MELVINS, SLEEP, PRIMORDIAL), mixed by Anderson, and mastered by Justin Weis (HAMMERS OF MISFORTUNE, LUDICRA, SLOUGH FEG).
Metal Underground .com
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That is, a simple alga like Volvox and a complex metazoan like an octopus both occupy the same sublevel.
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Comparisons of the roles of homeobox genes in metazoan development are playing a pivotal role in the current resynthesis of developmental and evolutionary biology.
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Hobmayer B, Rentzsch F, Kuhn K, Happel CM, von Laue CC, et al. (2000) WNT signalling molecules act in axis formation in the diploblastic metazoan Hydra.
PLoS ONE Alerts: New Articles
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It's the adjective of coelom SEE-lum, which Merriam-Webster said is "the usually epithelium-lined space between the body wall and the digestive tract of metazoans above the lower worms," which told me basically nothing.
Languagehat.com: COELOM.
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In addition to their relevance as model organisms for understanding metazoan evolution, anthozoans are ecologically important.
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In other words, much of metazoan evolution was cryptic, bound up in tiny animals devoid of skeletons and perhaps surviving as interstitial benthic microfauna.
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I conceived the embryonic form, in which the whole structure consists of only two layers of cells, and is known as the gastrula, to be the ontogenetic recapitulation, maintained by tenacious heredity, of a primitive common progenitor of all the Metazoa, the Gastraea.
Evolution in Modern Thought
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However, given that H1 is not essential in simple metazoans, such as filamentous fungi and also in specialized protozoa, we have good reason to suspect it might likewise be nonessential for less specialized protozoa.
Another Protozoan and Front-Loading
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A metazoan body develops as the egg cleaves into cells that then proliferate in a branching pattern of mitoses to produce a cell tree.
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According to Haeckel, the gastrula stage can be found in the development of all animals, and represents the recapitulation of the ancestral metazoan, the Gastraea, a diploblastic animal with a ciliated gut.
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The mitochondrial genome of this animal is multipartite and exists as a population of small circular DNAs of different sizes and gene contents, a unique organization among studied metazoans.
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You then cited publications where Woese, Doolittle, and others, affirm their faith in the monophyly of Eukarya, Metazoa, chimps and humans, whatever.
A Disclaimer for Behe?
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Another oceanic resident, the quahog clam (Arctica islandica), is thought to be one of the longest lived metazoans of all.
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Consider two classes of transcription factors that are known to play crucial roles in metazoan development: the T-box proteins and the SOX proteins.
2008 April - Telic Thoughts
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Haeckel maintained that the "gastrula" stage occurred in the development of all Metazoa, and that it was typically formed, by invagination, from
Form and Function A Contribution to the History of Animal Morphology
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The late Neoproterozoic is an important period of biological evolution; and the emergence of metazoa is a representative event, which marked the history of biology evolution having entered a new era.
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In recent years, much progress has been made in understanding of the evolution of metazoan developmental mechanisms.
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We have a common ancestor that evolved intercellular signalling (for e.g. colonialism, mating), a function which was expanded in certain lineages, (esp. metazoans that used those signally functions to coordinate across specialized tissues).
Biomolecular Networks
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The specific process of apoptosis first appeared with the evolution of metazoan animals and has been well conserved in all animal phyla.
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Planula" theory, according to which the ancestral form of the Metazoa was a two-layered closed sac formed typically by delamination, less often by invagination.
Form and Function A Contribution to the History of Animal Morphology
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As in the case of sexual propagation, so in that of karyokinesis, processes which are common to all the Metazoa are not wholly without their foreshadowings in the
Darwin, and After Darwin (Vol. 1 and 3, of 3) An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions
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There is a treasure trove in China: the well-preserved phosphatized embryos of the Doushantuo formation, a sampling of the developmental events in ancient metazoans between 551 and 635 million years ago.
Dissecting embryos from half a billion years ago - The Panda's Thumb
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The early metazoans, the hypothetical Urmetazoa, lived in an aquatic environment and consequently were exposed to a massive load of both pro- and eukaryotic organisms trying to invade and destruct them.
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Still others may belong to poorly known metazoan taxa that may or may not belong in any known phyla, and others are probably too poorly preserved to be informative.
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If cloning by fission is viewed more generally as a form of tissue modeling seen in all metazoans, in which some cells proliferate and others die, knowledge from other organisms can suggest candidate genes.
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Yet it is evident that the fact of all the processes above described being so similar in the case of sexual (or metazoal) reproduction among the innumerable organisms where it occurs, constitutes in itself a strong argument in favour of evolution.
Darwin, and After Darwin (Vol. 1 and 3, of 3) An Exposition of the Darwinian Theory and a Discussion of Post-Darwinian Questions
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Early metazoan evolution, prior to the emergence of the clade that gave rise to crown taxa, involved a number of innovations.
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One widely-mooted suggestion is that planktotrophic larvae, typified by the annelidan trochophore and echinoid pluteus, existed long before the metazoan radiations evident in the Cambrian fossil record.
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Thus, characters shared by chaetognaths and chordates are only those shared by all triploblastic metazoans and resolution of affinities depends upon adopting a preferred hypothesis of relationship.
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Halkieriids were sluglike metazoans armored with a coat of mineralized sclerites and two prominent shells at either end.
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The genes have an arrangement relatable to those of coelomate metazoans, but not to those of secernentean nematodes.
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Halkieriids were sluglike metazoans armored with a coat of mineralized sclerites and two prominent shells at either end.
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If I were a FLID supporter, I would propose that the homeobox regulatory mechanism for body regions was a "front-loaded design element" that, once it was in place, could be modified extensively via standard evolutionary mechanisms to produce the various metameric metazoan bauplans.
Ancient Predator Revealed!
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Given the likelihood that the ctenophore lineage is the deepest branch among metazoans, let's have a closer look at the toolkit contained by these creatures to determine if the basic theme of front-loading evolution continues to hold up.
As Expected
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Complete mtDNA nucleotide sequences are available for a total of 76 species, of which 58 are metazoan.
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He briefly discusses a recent paper where "The authors concluded that gene loss had been a substantial factor in evolution, and that" the ancestral metazoan is likely to have been much more complex than was previously imagined.
Circus of the Spineless
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You didn't answer this question, but said that molecular homology does indicate vertical descent (common ancestry from an actual cell) in Metazoa, “the group located above the Darwinian threshold.”
A Disclaimer for Behe?
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The dicyemid mesozoans, once hypothesized to be non-bilaterian metazoans, have since been shown to possess central class Hox genes indicating that these enigmatic parasites are secondarily simplified bilaterians.
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Autophagy is commonly observed in metazoan organisms during programmed cell death (PCD), but its function in dying cells has been unclear.
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A data dump now about problems with metazoan (or chordate or mammalian) phylogeny would be getting ahead of the discussion.
A Disclaimer for Behe?
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If so, the oldest traces of locomotory activities of the metazoans should be connected with their infaunal life.
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Metazoans inherited a genome of some still undetermined size, but certainly numbering many thousands of genes, from their protistan ancestor.
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In metazoans, the bulk of the cohesin complex is displaced at prophase, but a subset of cohesin complexes is maintained at the centromere and perhaps other sites.
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The first seems to have occurred before the split between poriferans and the other metazoans.
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A data dump now about problems with metazoan (or chordate or mammalian) phylogeny would be getting ahead of the discussion.
A Disclaimer for Behe?
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We have found that appendicularians, the most abundant microphagous metazoans, strongly stimulate the magnitude of experimentally induced blooms and that this effect can be scaled to any appendicularian density.
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We can repeat the exercise if you like for Metazoa, Chordata, etc.
A Disclaimer for Behe?
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Although we cannot completely exclude a nonbiological or nonmetazoan origin, we identified what appear to be modern cnidarian developmental stages, including both anthozoan planula larvae and hydrozoan embryos.
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The Cambrian fossil record suggests that many metazoans were macroscopic and adapted for life in the macrobenthos.
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The important point for us is that, just as all Metazoa were considered by Haeckel to be descended from the Gastræa, so all Coelomati were held by the Hertwigs to be derived from an original coelomate _Urform_.
Form and Function A Contribution to the History of Animal Morphology
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So the monophylic clade of metazoa contains only multicellular liveforms, this also defines the mentioned outgroups of taxa from protozoa and prokaryota.
A Disclaimer for Behe?
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These proteins play essential roles in metazoan development and are considered part of the developmental toolkit as outlined by biologist Sean Carroll.
2007 September - Telic Thoughts
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The main assumption was that the neural or blastoporal surface must be homologous throughout the Metazoa, though it was dorsal in the Chordata, ventral in the Annelida and Arthropoda.
Form and Function A Contribution to the History of Animal Morphology
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Sponges and diploblasts (cnidarians and ctenophores) are basal to the triploblastic metazoans.
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It even remained unclear if Porifera share one common ancestor with other metazoan phyla.
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Conflicting evidence on the position of brachiopods in metazoan phylogeny exists.
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Some said that the original embryonic form of the metazoa was not the gastrula, but the "planula" -- a double-walled vesicle with closed cavity and without mouth-aperture; the latter was supposed to pierce through gradually.
The Evolution of Man — Volume 1
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A consensus is beginning to emerge regarding many key nodes in basal metazoan and cnidarian phylogeny, but many important questions remain.
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As compared to metazoans, the development of these unicellular organisms is likely less affected by dissociated heterochrony, which is considered a common phenomenon in metazoans.