Eg a caterpillar or tadpole (5)
I believe the answer is:
larva
I believe this is a double definition.
'eg a caterpillar' is the first definition.
(caterpillar is a kind of larva)
'tadpole' is the second definition.
(I've seen this before)
(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" .)