Examples of representing beings: sharks, rays, sardines, tuna, salmons. Basic morphology: hydrodynamic body, fins; cartilaginous skeleton in chondrichthyes, bony skeleton in osteichthyes. Skin: with scales in osteichthyes and placoid scales in chondrichthyes. Respiration: branchial. Circulation: closed, incomplete, heart with two chambers. Nitrogen waste: urea in chondrichthyes, ammonia in osteichthyes. Thermal control: heterothermic. Types of reproduction: **, internal fecundation in chondrichthyes, external in osteichthyes.
