Chondrichthyes and Osteichthyes

Chondrichthyes: Cartilaginous endoskeleton, ventral mouth, placoid scales, no air bladder (swim constantly to avoid sinking), internal fertilization (e.g., Shark/Scoliodon); Osteichthyes: Bony endoskeleton, terminal mouth, cycloid/ctenoid scales, air bladder present (regulates buoyancy), mostly external fertilization (e.g., Rohu, Catla).