Ocean sunfish

Ocean sunfish have a very peculiar appearance.

An excerpt from the article 20 facts about Ocean sunfish
The body is tall, laterally flattened with a crescent-shaped tail that replaced the caudal fin in the course of evolution. Ocean sunfish tail is called clavus. Dorsal and anal fins are elongated and almost vertically oriented. The pectoral fins are relatively small and have a fan-like shape.