Heterocercal vs. Homocercal

Heterocercal (adjective)

Of a fish’s tail, such that the vertebral column bends and extends upwards into the upper lobe of the tail, making it larger than the lower lobe; as in sharks, rays, and skates.

Homocercal (adjective)

Describing the symmetric tail of a fish that has two lobes extending from the end of the vertebral column.