From The Anomalocaris Homepage:
Over half a billion years ago, the great Cambrian diversification of life generated the majority of animal phyla that live in the world today. Among the results were the world's first great predators: Anomalocaris and related genera of large, active, swimming, visual hunters with spiny grasping appendages and weird, circular mouths lined with teeth. They include some of the largest known Cambrian animals, and their presence implies a complex ecosystem present in the early Phanerozoic.
What is most interesting about this alien-looking monstrosity are the "spiny grasping appendages" on either side of the circular tooth lined mouth. This is a body form that screams "cthulhoid".