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Trichoplax
''Trichoplax adhaerens'' is the only extant representative of phylum Placozoa, which is a basal group of multicellular animals (metazoa). ''Trichoplax'' are very flat organisms around a millimetre in diameter, lacking any organs or internal structures. They have two cellular layers: the top epitheloid layer is made of ciliated "cover cells" flattened toward the outside of the organism, and the bottom layer is made up of cylinder cells that possess cilia used in locomotion, and gland cells that lack cilia.〔(【引用サイトリンク】 accessdate = 2015-10-04 )〕 Between these layers is the fibre syncytium, a liquid-filled cavity strutted open by star-like fibres.
''Trichoplax'' feed by absorbing food particles—mainly microbes—with their underside. They generally reproduce asexually, by dividing or budding, but can also reproduce sexually. Though ''Trichoplax'' has a small genome in comparison to other animals, nearly 87% of its 11,514 predicted protein-coding genes are identifiably similar to known genes in other animals.
==Discovery==
Trichoplax was discovered in 1883 by the German zoologist Franz Eilhard Schulze, in a seawater aquarium at the Zoological Institute in Graz, Austria. The generic name is derived from the classical Greek ('), "hair", and ('), "plate". The specific epithet ''adhaerens'' comes from Latin "adherent", reflecting its propensity to stick to the glass slides and pipettes used in its examination.
Although from the very beginning most researchers who studied ''Trichoplax'' in any detail realized that it had no close relationship to other animal phyla, the zoologist Thilo Krumbach published a hypothesis that ''Trichoplax'' is a form of the planula larva of the anemone-like hydrozoan ''Eleutheria krohni'' in 1907. Although this was refuted in print by Schulze and others, Krumbach's analysis became the standard textbook explanation, and nothing was printed in zoological journals about ''Trichoplax'' until the 1960s. In the 1960s and 1970s a new interest among researchers led to acceptance of Placozoa as a new animal phylum. Among the new discoveries was study of the early phases of the animals' embryonic development and evidence that the animals that people had been studying are adults, not larvae. This newfound interest also included study of the organism in nature (as opposed to aquariums).
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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