Plenocaris plena is a genus of extinct bivalved hymenocarine arthropod that lived in the Cambrian aged Burgess Shale[1] and Chengjiang.

Unlike waptiids, but similar to Synophalos, the tail flukes lack segmentation.

[5] It has been suggested to be a member of Hymenocarina, which contains numerous other Cambrian bivalved arthropods.

[6] Some specimens have been found with sediment within the gut tract, suggesting it was a deposit feeder.

(1983), "Affinities and early evolution of the Crustacea: the evidence of the Cambrian fossils", Crustacean Issues