Which of the following is $NOT$ a characteristic of $Cyclostomata$?

What is found in the skin of Cyclostomata?

Petromyzon belongs to

The jawless vertebrate is

Animals of this class are marine,but migrate to freshwater for spawning.

Select the incorrect statements with respect to Cyclostomes:
$(a)$ They lack scales and paired fins.
$(b)$ They have a circular mouth with jaws.
$(c)$ They bear $6-15$ pairs of gills.
$(d)$ They migrate to deep sea for spawning.
Choose the most appropriate answer from the options given below: