Notes from NEET topper
Class – Chondrichthyes
These marine animals are characterized by their streamlined bodies and possess a cartilaginous endoskeleton. Their mouths are situated on the ventral side, and they maintain a persistent notochord throughout their entire lives. These creatures have separate gill slits without an operculum (gill cover), and their skin is tough, featuring minute placoid scales. Their teeth are modified placoid scales that are backwardly directed, and they have powerful jaws, making them predatory animals.
To stay afloat, they must continuously swim as they lack an air bladder. Their hearts consist of two chambers, one auricle and one ventricle. Some species, like the Torpedo, possess electric organs, while others, like the Trygon, have poison stings. They are cold-blooded, meaning they are unable to regulate their body temperature (poikilothermic). These animals have separate sexes, with males having claspers on their pelvic fins. They reproduce through internal fertilization, and many of them are viviparous, giving birth to live young.
Notable examples of these creatures include Scoliodon (Dogfish), Pristis (Sawfish), Carcharodon (Great White Shark), and Trygon (Stingray).
