(d) : Order Cetacea includes whales, dolphins and porpoises. These are the most highly modified mammals. They have a fish-like body with smooth, hairless skin devoid of sweat and oil glands, far posterior nares, small eyes, minute ear openings without pinnae, paddle-like forelimbs, no hind limbs, abdominal testes and flattened tail ending in two horizontal flaps or flukes.