Seahorse is the name given to 54 species of small marine fishes in the genus Hippocampus. "Hippocampus" comes from the Ancient Greek word hippos meaning "horse" and kampos  meaning "sea monster". Having a head and neck suggestive of a horse, seahorses also feature segmented bony armor, an upright posture and a curled prehensile tail. Seahorses, along with pipefish, belong to the family Synathidae. Common features include elongated bodies, protruding bony rings and a skinny tubular snout tipped with a tiny toothless mouth; seahorses feed primarily on plankton and tiny benthic animals. 

The male of the species caries the babies and delivers them. The dorsal fin on the seahorse's back is its most powerful means of propulsion; fluttering up to 70 times per second. A pair of pectoral fins behind the seahorse's head help with steering and braking. Because of their inability to move quickly, seahorses live a relatively stationary existence, typically inhabiting regions of the reef where there is little or no current.

They are often territorial and stay in the same location making it easy for a dive master to remember where one was last seen. 

They do not spook easily so if you are fortunate enough to find one they are relatively easy to photograph. 

Good luck hunting.