Class 1. Chondrichthys or Elasmobranchi

• Generally found in seawater and include largest fishes that over lived.
• The exoskeleton is in the form of placoid scales.
• Endoskeleton is cartilaginous (with some calcification but no ossification in living forms).
• Placoid scales on the body or the skin is naked.
• There are 5 to 7 pairs of gills and gill clefts without operculum.
• There is no air bladder.
• A cloaca is present.
• External gill openings are separate. They are not covered by operculum.
• Heterocercal caudal fin is seen.
• Males show claspers for copulation.