Pisces is a subclass in the subphylum Vertebrata of the Phylum Chordata, and thus contain all of the characteristics of both of these groups in addition having skin covered in scales, being ectothermic, laying soft shelled eggs that must be laid in water, and needing to perform external fertilization. As well as this, all members are fully aquatic, their limbs modified into fins, and gas is exchanged through gills.