Flame cells are also called $A$ and they are found in animals like $B$.

• A
  $A$ - Salt excreting glands,$B$ - marine birds
• B
  $A$ - Protonephridia,$B$ - rotifers
• C
  $A$ - Metanephridia,$B$ - Echinoderms
• D
  $A$ - Nephrons,$B$ - Crustaceans