Eg a caterpillar or tadpole (5)
I believe the answer is:
larva
<span class="explanation-format__ClueExplanation">I believe this is a double definition.<br/ ><br/ >'<span class="explanation-format__original">eg a caterpillar</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(caterpillar is a kind of larva)</span><br/ ><br/ >'<span class="explanation-format__original">tadpole</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ ></span>
(Other definitions for larva that I've seen before include "Immature form of caterpillar" , "Insect in the first post-egg stage of its life" , "Grub; insect" , "shows form of immaturity" , "early form" .)