The Seahorse is a marine fish with a prehensile tail who breathes through its gills. The prehensile tail means it can attach and hang on to objects, and it is the only group of fish that has this feature. (Prehensile tails are more often associated with mammals and reptiles, such as monkeys, possums, rats, snakes, and some lizards). The seahorse is of the genus Hippocampus, the name being derived from the Ancient Greek word hippos meaning "horse" and kampos meaning "sea monster." There are 54 species of these small fish, and they usually live in shallow tropical waters.