Chondrichthyes refers to a class of fish or vertebrates that feature paired fins and an internal skeleton composed of cartilage. Noticeable characteristics of cartilaginous fish include the capability of numerous species to breathe through gills and spiracles, skin dressed in dermal denticles to give protection, a small brain with several sensory organs, and an adaptive immune system. Additionally, these fish lack swim bladders, are often predatory, and show jaws and paired appendages. They are likewise an excellent source of food for humans. Chondrichthyes are further divided into Elasmobranchii and Holocephali and can be found both in freshwater and marine environments.