Anomalocaris

Anomalocaris ("abnormal shrimp") or ("odd shrimp") was a marine arthropod that lived in the Middle Cambrian. Its strange appearance caused much confusion to its discoverers. It was the world's first top predator.

Description
Anomalocaris looks like something out of a 50s alien movie. It averaged a length of 1 meter, which was a large size for its time compared to other forms of life such as Hallucigenia. The lobes on the sides of its body acted like a single fin, and were used to propel itself through the water. It had compound eyes, a strange ring-shaped mouth, and two appendages on the front of the head that were used to catch prey (as Anomalocaris was almost certainly a predator).

Discovery
The history of Anomalocaris is just as confusing as its appearance. Its "arms" were first found in 1892, and assigned to a crustacean. The mouth was later discovered in the Burgess Shale by Charles Walcott, and given to a species of jellyfish. Then the body was discovered, but that was named for a sponge! Later it was realized that they all came from the same animal and so was given its first name, Anomalocaris, as the "arms" were discovered first and that was the name given to them.