Plenocaris

Plenocaris plena is a genus of extinct bivalved hymenocarine arthropod that lived in the Cambrian aged Burgess Shale^[1] and Chengjiang.^[2] Originally described as a species of Yohoia by Walcott in 1912, it was placed into its own genus in 1974.

Plenocaris Temporal range: Chengjiang–Burgess shale PreꞒ Ꞓ O S D C P T J K Pg N
Fossil of Plenocaris plena from the Burgess shale
Life restoration
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Clade:	Mandibulata
Order:	†Hymenocarina
Family:	†Waptiidae
Genus:	†Plenocaris Whittington, 1974
Species:	†P. plena
Binomial name
†Plenocaris plena (Walcott, 1912)
Synonyms
Yohoia plena Walcott, 1912

The head has a pair of simple antennae. The body has 13 tergites, with trunk tergites 2 to 4 having pairs of elongate and uniramous appendages, with appendages absent from the other body segments.^[3] The body terminates with paired tail flukes. Unlike waptiids, but similar to Synophalos, the tail flukes lack segmentation.^[4] 106 specimens of Plenocaris are known from the Greater Phyllopod bed, where they comprise 0.20% of the community.^[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. The lack of swimming appendages means that swimming was likely primarily accomplished with movement of the trunk and tail fan.^[3]