Immature creature picked up from volcanic discharge (5)
I believe the answer is:
larva
'immature creature' is the definition.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for larva that I've seen before include "Insect in the first post-egg stage of its life" , "Grub of e.g. beetle" , "Immature form of an insect before metamorphosis" , "Animal in immature state" , "Immature form of caterpillar" .)