Presence of claspers is an important character in

Which of the following statements are not true about shark?
$a$. The skin is tough and covered with placoid scales
$b$. They possess a swim bladder which regulates buoyancy
$c$. The tail of shark is heterocercal
$d$. Ampulla of Lorenzini present in the snout of shark is a thermoreceptor.
$e$. It has five pairs of gill slits covered by operculum

Identify the figure.

In which of the following is a single-circuit heart found?

Which of the following has a cartilaginous and fibrous endoskeleton?

In males,pelvic fins bear claspers in: