Plenocaris

{{Short description|Extinct genus of arthropods}}

{{Speciesbox

| display_parents = 4

| fossil_range = {{fossil range|Chengjiang|Burgess shale}}

| image = USNM PAL 57700 Plenocaris plena Image 04.jpg

| image_caption = Fossil of Plenocaris plena from the Burgess shale

| image2 = Plenocaris.png

| image2_caption = Life restoration

| genus = Plenocaris

| parent_authority = Whittington, 1974

| species = plena

| authority = (Walcott, 1912)

| synonyms = * Yohoia plena Walcott, 1912

}}

Plenocaris plena is a genus of extinct bivalved hymenocarine arthropod that lived in the Cambrian aged Burgess Shale{{citation

| year = 1974

| last = Whittington

| first = Harry B.

| title = Yohoia Walcott and Plenocaris n. Gen., arthropods from the Burgess Shale, Middle Cambrian, British Columbia

| journal = Geological Survey of Canada Bulletin

| pages = 1–21

}} and Chengjiang.{{citation

| last1 = Hou | first1 = Xian-Guang

| last2 = Bergström | first2 = J.

| year = 1997

| title = Arthropods of the Lower Cambrian Chengjiang fauna, southwest China

| publisher = Scandinavian University Press

| journal = Fossils & Strata

| volume = 45

| pages = 116

}} Originally described as a species of Yohoia by Walcott in 1912, it was placed into its own genus in 1974.

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.{{Cite web |title=Plenocaris plena |url=https://burgess-shale.rom.on.ca/fossils/plenocaris-plena/ |access-date=2022-09-08 |website=The Burgess Shale |publisher=Royal Ontario Museum |language=en-US}} The body terminates with paired tail flukes. Unlike waptiids, but similar to Synophalos, the tail flukes lack segmentation.{{Cite journal |last1=Yang |first1=Jie |last2=Ortega-Hernández |first2=Javier |last3=Lan |first3=Tian |last4=Hou |first4=Jin-bo |last5=Zhang |first5=Xi-guang |date=2016-06-10 |title=A predatory bivalved euarthropod from the Cambrian (Stage 3) Xiaoshiba Lagerstätte, South China |journal=Scientific Reports |language=en |volume=6 |issue=1 |pages=27709 |doi=10.1038/srep27709 |pmid=27283406 |pmc=4901283 |bibcode=2016NatSR...627709Y |issn=2045-2322|doi-access=free }} 106 specimens of Plenocaris are known from the Greater Phyllopod bed, where they comprise 0.20% of the community.{{cite journal |last1=Caron |first1=Jean-Bernard |last2=Jackson |first2=Donald A. |date=October 2006 |title=Taphonomy of the Greater Phyllopod Bed community, Burgess Shale |journal=PALAIOS |volume=21 |issue=5 |pages=451–65 |doi=10.2110/palo.2003.P05-070R |jstor=20173022|bibcode=2006Palai..21..451C |s2cid=53646959 }} It has been suggested to be a member of Hymenocarina, which contains numerous other Cambrian bivalved arthropods.{{Cite journal |last1=Vannier |first1=Jean |last2=Aria |first2=Cédric |last3=Taylor |first3=Rod S. |last4=Caron |first4=Jean-Bernard |date=June 2018 |title=Waptia fieldensis Walcott, a mandibulate arthropod from the middle Cambrian Burgess Shale |journal=Royal Society Open Science |language=en |volume=5 |issue=6 |pages=172206 |doi=10.1098/rsos.172206 |issn=2054-5703 |pmc=6030330 |pmid=30110460|bibcode=2018RSOS....572206V }} 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.