Osteichthyes includes both marine and fresh water fishes with a bony endoskeleton. Their body is streamlined and the mouth is mostly terminal. They have four pairs of gills which are covered by an operculum on each side. The skin is covered with cycloid or ctenoid scales. An air bladder is present, which regulates buoyancy. The heart is two-chambered, with one auricle and one ventricle. They are cold-blooded animals. Sexes are separate. Fertilisation is usually external, and they are mostly oviparous with direct development. Examples include marine fishes such as Exocoetus (flying fish) and Hippocampus (sea horse); freshwater fishes such as Labeo (rohu), Catla (katla) and Clarias (magur); and aquarium fishes such as Betta (fighting fish) and Pterophyllum (angel fish). In the broad classification, Osteichthyes and Chondrichthyes together form super class Pisces because both bear fins for locomotion. The decisive points for the exam are the bony skeleton, the operculum covering four pairs of gills, the air bladder for buoyancy, cycloid or ctenoid scales, external fertilisation and direct development, all of which contrast directly with cartilaginous fishes and appear very often in comparison questions.