Definitions
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- noun Plural form of
placozoan .
Etymologies
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Examples
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Last year Signorovitch also spied some egglike structures, and when she did genetic tests on her placozoans, she found evidence of sex as incontrovertible as a stain on a blue dress.
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Sexual reproduction always mixes up DNA, and, as Signorovitch reports in a recent Proceedings of the National Academy of Sciences, placozoans have jumbled genes.
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Many marine invertebrates reproduce by budding, and since scientists never observed placozoans in coitus, they assumed the creatures were asexual, too.
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It is not clear whether p53 has the same function in placozoans.
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Philippe (Université de Montréal, Canada), Gert Wörheide (LMU Munich, Germany) and Michael Manuel (University of Paris, France) performed the most comprehensive study to date and investigated 128 genes from a total of 55 species - including nine poriferans, eight cnidarians, three ctenophores and the single known species of placozoans.
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Yet placozoans have a version of p53, also known as TP53, that is strikingly similar to ours, says
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"Since the comb jellies already have nerve and muscle cells, this would suggest that these features developed several times independently in animal history, or that they were lost in sponges and placozoans."
Latest Articles 2009
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"Since the comb jellies already have nerve and muscle cells, this would suggest that these features developed several times independently in animal history, or that they were lost in sponges and placozoans," explains the LMU researcher.
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Hence The complex history of cnidarian Hox genes and its bearing on early Hox evolution concerning the presence of true Hox genes in cnidarians and bilaterians and their probable absence from sponges, ctenophores and placozoans, leading to the conclusion that this gene family originated in an exclusive cnidarian / bilaterian ancestor, or was lost in other metazoan lineages
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After comparing the sequences of 104 Trichoplax genes with their counterparts in other organisms, they concluded that placozoans aren't the oldest animals; they branched off after sponges but before cnidaria.
Darwiniana 2008
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