Cartilaginous fishes possess which type of scales?

Which of the following is known as a living fossil?

Match the following:

Column-$I$	Column-$II$
$(1)$ $Scoliodon$	$(p)$ $Saw$ $fish$
$(2)$ $Pristis$	$(q)$ $Sting$ $ray$
$(3)$ $Carcharodon$	$(r)$ $Dog$ $fish$
$(4)$ $Trygon$	$(s)$ $Great$ $white$ $shark$

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.

The heart of a fish is different from other vertebrate groups because:

What is the location and function of claspers?