why chrysophytes are known as pearls of ocean?

Solution:

Diatoms are considered as chrysophytes. 
The diatoms- the unique organisms - are sometimes called the jewels of the sea because of their distinctive cell walls. The cell wall of diatoms is chiefly composed of cellulose impregnated with glass like silica. It shows sculpturing and ornamentations. That is why, the chrysophytes are also called as 'pearls of the ocean'.