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Proarticulata
Proarticulata is an extinct phylum of very early, superficially bilaterally symmetrical animals known from fossils found in the Ediacaran (Vendian) marine deposits, and dates to approximately .
The name from Greek ''προ'' (pro-) = "before" and Articulata, i.e. prior to animals with true segmentation such as annelids and arthropods. This phylum was established by Mikhail A. Fedonkin in 1985 for such animals as ''Dickinsonia'', ''Vendia'', ''Onega'', ''Praecambridium''〔M. A. Fedonkin (1985). "Systematic Description of Vendian Metazoa". In Sokolov, B. S. and Iwanowski, A. B., eds., "Vendian System: Historical–Geological and Paleontological Foundation, Vol. 1: Paleontology". Moscow: Nauka, pp. 70–106.〕 and currently many other Proarticulata are described (see list).
The transverse articulation (division) of the Proarticulata body into isomers is distinct from the transverse articulation segments in annelids and arthropods, as their individual isomers occupy only half the width of their bodies, and are organized in an alternating pattern along the longitudinal axis of their bodies. In other words, one side is not the direct mirror image of its opposite (''chirality''). Opposite isomers of left and right side are located with displacement of half of their width. This phenomenon is described as the symmetry of gliding reflection.〔〔
== Morphology ==
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