Electric organ is present in

Identify the figure.

Which of the following has a cartilaginous endoskeleton?

In $Chondrichthyes$,the heart possesses:

The most poisonous fish is

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