Which of the following is an incorrect pair?

Which of the following classes of protozoa is exclusively endoparasite?

What is the meaning of the term $Protozoa$?

$A$ stiff cell wall and biflagellate cells are characteristic features of which group?

Two species of Amoeba $X$ and $Y$ were kept in fresh water and adapted to it. Species $X$ developed a contractile vacuole. When both were transferred to sea water and adapted,both $X$ and $Y$ lost their contractile vacuole. From these observations,we conclude that:

In which animal phylum is the organism $Opalina$ classified?