1.  hippocampus(n = noun.body) - a complex neural structure (shaped like a sea horse) consisting of grey matter and located on the floor of each lateral ventricle; intimately involved in motivation and emotion as part of the limbic system; has a central role in the formation of memories;
is a kind of neural structure
is a part of limbic brain, limbic system, visceral brain

2.  hippocampus(n = noun.animal) genus hippocampus - seahorses;
is a kind of fish genus
is a member of family syngnathidae, syngnathidae

1.  A fabulous monster, with the head and fore quarters of a horse joined to the tail of a dolphin or other fish (Hippocampus brevirostris), -- seen in Pompeian paintings, attached to the chariot of Neptune. Fairholt. [1913 Webster]

2.  A genus of lophobranch fishes of several species in which the head and neck have some resemblance to those of a horse; -- called also sea horse. [1913 Webster]
" They swim slowly, in an erect position, and often cling to seaweeds by means of the incurved prehensile tail. The male has a ventral pouch, in which it carries the eggs till hatched." [1913 Webster]

3.  A name applied to either of two ridges of white matter in each lateral ventricle of the brain. The larger is called hippocampus major or simply hippocampus. The smaller, hippocampus minor, is called also ergot and calcar. [1913 Webster]

hippocampus, n. (pl. hippocampi)
1 any marine fish of the genus Hippocampus, swimming vertically and with a head suggestive of a horse; a sea horse.
2 Anat. the elongated ridges on the floor of each lateral ventricle of the brain, thought to be the centre of emotion and the autonomic nervous system.

Etymology:
L f. Gk hippokampos f. hippos horse + kampos sea monster

genus hippocampus