A sea horse is a small ocean fish with a head shaped like a horse's head, a curled tail, and a body covered in bony plates instead of scales. Sea horses swim upright, using a tiny fin on their back that flutters up to 35 times per second. They steer with small fins near their heads and use their curled tails to grip onto seaweed or coral, anchoring themselves so ocean currents don't sweep them away.

Sea horses are unusual fish in many ways. Unlike most fish that dart through water, sea horses move slowly and carefully, almost hovering in place. They hunt by ambushing tiny shrimp and plankton, sucking them up through their long snouts like living straws. Most remarkably, male sea horses carry the babies: the female deposits eggs into a special pouch on the male's belly, where he keeps them safe until they're ready to be born.

Sea horses range from half an inch to over a foot long, depending on the species. They live in shallow tropical and temperate waters around the world, camouflaging themselves among seagrasses and coral. Some can change color to blend in with their surroundings. Because they swim so slowly and live in delicate coastal habitats, sea horses are vulnerable to pollution and habitat loss.