Muggles' Guide to Harry Potter/Magic/Hippocampus

Overview
Hippocampi are the equine equivalent of Muggle "mermaids": forequarters and head of a horse, and tail of a fish.

Extended Description
The Hippocampus is largely a Mediterranean beast, though a single example was caught off the coast of Scotland by Mermen in 1949.

Analysis
While the Hippocampus does not appear in the main story, it does appear in the stated form in Muggle mythology. The name has also been used to identify a part of the structure of the brain which is apparently somehow involved with the creation and storage of memories.