Sanctarcaris was a 4" predatory arthropod that hunted on the Cambrian sea floor of what is now the Burgess Shale. It fed on creatures such as Opabinia, Marrella, and trilobites.
Sanctacaris had a wide, flattened head, ten finger-like limbs that forced food into its mouth, and a powerful tail called a telson. Sanctacaris, like other swimming arthropods of the Cambrian seas, had undulating fins along its side which helped it swim.
Sanctacaris also had predators. Its predators were Hurdia Victoria,
probably Leanchoilia, and all species of Anomalcaris,