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| Xenosome
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A particle collected from the environment and cemented into the organic matrix of a wall. Typically used for foreign mineral matter incorporated into the wall of testate amoebae or other agglutinate-wall-building protists. Xenosomes are distinguished from idiosomes. The latter are secreted de novo within cytoplasmic vesicles. The chemical composition of xenosomes, collected from the environment, depends in part on the availability of particles; however, in testate amoebae, species-specific selection, based on chemical composition of the particles, has been reported. (Although not in reference to a surface structure, the word “xenosome” has recently been introduced into the evolutionary protistological literature as a name for an intracytoplasmic or intranuclear organelle or body that contains DNA and is membrane-bounded and that is, or historically is presumed to have been, an endosymbiotic entity within a given protistan cell, having invaded or been engulfed by the host organism in the recent or distant past, subsequently becoming a more or less permanent inclusion in the host body, e.g., Kappa particles in the ciliate Paramecium and the plastids and mitochondria so common in protists belonging to many taxonomic groups.) [Link to this definition]
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