Nereocaris is an extinct genus of bivalved hymenocarine arthropod that lived in the Cambrian aged Burgess Shale in what is now British Columbia around 506 million years ago.

The holotype and paratype were found in the Burgess Shale Lagerstätte, in the Tulip Beds; it was later described in 2012, by Legg et al, as a basal hymenocarine, naming the type species Neroecaris exilis.

The specific name exilis comes from Latin, meaning slim; while the second species' name briggsi means "of Briggs", referring to professor Derek Briggs, an expert on Cambrian arthropods.

[2] Nereocaris exilis was relatively large sized arthropod for the era, with the largest specimen measuring up to 142 millimetres (0.466 feet).

The shape of its armor made it so the legs had a very limited range of movement, barely being able to reach whatever was directly under them.