Class Chondrichthyes :
• Have cartilagenous endoskeleton.
• Mouth ventral.
• Gill slits without operculum.
• Skin has placoid scales.
• Usually oviparous, fertilisation internal.
• No air bladder, so swim constantly to avoid sinking.
• Teeth are backwardly directed, modified placoid scales.
• Notochord is persistent throughout life. Males have claspers on pelvicfins.
• e.g., Torpedo, Trygon, Scoliodon.
Class Osteichthyes :
• Have bony endoskeleton.
• Mouth is usually terminal.
• Four pairs of gill slits covered by operculum.
• Skin has cycloid/ctenoid scales.
• Usually viviparous, fertilisation external.
• Have air bladder which regulates buoyancy.
• e.g., Hippocampus, Labeo, Catla, Betta.
