- Sea cows (which include manatees and dugongs) are aquatic mammals belonging to the order Sirenia. - Sea horses are small marine fish belonging to the genus Hippocampus. They are a type of fish, not a mammal. - Sea lions are marine mammals characterized by external ear flaps, long foreflippers, the ability to walk on all four flippers on land, and short, thick hair. They belong to the family Otariidae.