Caterpillar perhaps showing some cellular variation (5)
I believe the answer is:
larva
'caterpillar perhaps' is the definition.
(caterpillar is a kind of larva)
'some cellular variation' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'LARVA' can be found hidden inside 'cellular variation'.
'showing' acts as a link.
(Other definitions for larva that I've seen before include "Juvenile form of insect" , "Worm-like insect before metamorphosis" , "Woodworm" , "Caterpillar, for example" , "Animal in immature state" .)