Young frog (7)
I believe the answer is:
tadpole
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">young frog</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for tadpole that I've seen before include "Larval form" , "immature sea squirt" , "Frog in formation" , "Larval toad" , "Immature amphibian" .)