In Secret Agent Clank, they appeared in Prison and had a crown on their heads, probably denoting their 'King' status.
A simple way to kill a King Amoeboid was with a shot from the Nitro Eruptor or a charged up blast from the Shock Cannon.
Spiky king amoeboid
Spiky King Amoeboids were an odd variant of the King Amoeboid. The Spiky King Amoeboids only appeared in the upper levels of Aquatos sewers accessed using the Gravity Boots. Despite being more imposing and being encountered later than King Amoeboids, theye were much weaker, as they possessed half the health of a Large Amoeboid. Like King Amoeboids and relinquished a sewer crystal once they were defeated; however, they would drop out of ceiling sections of the sewers instead of appearing from large walls of slime. They are the most silent enemies in the game and their eyes are not glowing.