any of a genus (Hippocampus) of small, semitropical, marine bony fishes of the same family (Syngnathidae order Gasterosteiformes) as the pipefishes, having a slender prehensile tail, plated body, and a head and foreparts somewhat suggestive of those of a horse, and the male of which incubates the eggs in a pouch in his abdomen; a sea horse.

a sea horse - a) a massive, arctic sea carnivore (Odobenus rosmarus) of the same family (Otariidae) as the eared seals, having two tusks projecting from the upper jaw, a thick mustache, a very thick hide, and a heavy layer of blubber; a walrus; b) any of various fishes of the genus Hippocampus of the pipefish family (esp. Hippocampus hudsonius) having a prehensile tail, an elongated snout, and a head bent at right angles to the body; c) (myth.) a sea monster with the head and forequarters of a horse and the tail of a dolphin or fish; a hippocampus.