The hypocampus is a mythical crature with the upper body or head of a horse and the lower body or tail of a fish.
target: http://www.bellaonline.com/articles/art35491.asp
Also hippocampus In Greek mythology, the hippocampus (horse-like sea monster") was a mythical monster, half-horse, half-sea-monster. One of them pulled Poseidon's chariot. It looked like a horse with the rear part resembling a fish or dolphin.
target: http://www.websters-online-dictionary.org/definition/hippocampus
The hippocampus was a fabled sea animal from Greek mythology. It was found in classical myth. It resembles a horse with the hind parts of a fish or dolphin. The chariot of Poseidon was drawn by a hippocampus. The name comes from the Greek hippos, horse; and kampos, sea monster.