Protozoan (6)
I believe the answer is:
amoeba
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">protozoan</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I know that amoeba is a type of rhizopod)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for amoeba that I've seen before include "Unicellular creature" , "Basic life form" , "Unicellular form" , "cell for life" , "Protozoon" .)