In which of the following animals,the heart does not have the left and right auricles?

Which of the following statements are not true?
$a$. Dermal scales of fishes form the exoskeleton.
$b$. Cycloid and ctenoid scales have distinct lines of growth which aid in determining the age of the fish.
$c$. Fish scales are never shed.
$d$. The skin in elasmobranchs is covered with placoid scales.
$e$. The development of a placoid scale is not like the development of a tooth.

Which of the following animal groups correctly matches its characteristic without any exceptions?

Which of the following is a true fish?

Which sensory organ is found as a unique feature in fishes?

Which one of the following groups of animals is correctly matched with its characteristic feature without any exception?