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Abstract - Restudy of Yunnanopleura, Tchangsichiton, Runnegarochiton, Meishucunchiton, Yangtzechiton and Luyanhaochiton from the earliest Cambrian in the Yangtze Region of China confirms the appearance of the Polyplacophora in the earliest Cambrian. It also suggests an origin for the class in late Proterozoic. Yangtzechiton and Luyanhaochiton, represented in the study material, are typical polyplacophorans having head, intermediate and tail valves, each with a tegmentum and an articulamentum. These morphologic features establish their distinction from the non-molluscan genus Paracarinachites. The polyplacophoran character of species of the genera Yunnanopleura, Tchangsichiton, Meishucunchiton and Gotlandchiton? is demonstrated by the presence of discrete areas (central or jugal, lateral) on the mtermediate valves. Yunnanopleura is probably ancestral to the Early Ordovlclan Chelodes Davidson and King. Runnegarochiton appears to be closely related to the Middle Ordovician Priscochitan Dall.

Author(s) WEN, YU : Part 2
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