Undeveloped creature right inside molten rock (5)

I believe the answer is:

larva

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'undeveloped creature' is the definition.
'larva' can be an answer for 'creature' (larva is a kind of animal). I am not certain of the 'undeveloped' bit.

'right inside molten rock' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' indicates putting letters inside.
'molten rock' becomes 'lava' (I've seen this in another clue).
'r' placed into 'lava' is 'LARVA'.

Can you help me to learn more?

(Other definitions for larva that I've seen before include "Volcanic outpouring" , "Maggots" , "Insect's immature form" , "Grub; insect" , "Tadpole or caterpillar, say" .)

I've seen this clue in The Times.

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