Crossword Genius

What mollusc inhabits ocean’s lower regions? (8)

Ross

I believe the answer is:

seashell

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'what mollusc inhabits' is the definition.
I can't judge whether this definition defines the answer.

'ocean's lower regions?' is the wordplay.
'ocean's' becomes 'seas' ('sea' can be a synonym of 'ocean').
'lower regions?' becomes 'hell' (I have seen 'Infernal regions' mean 'hell' so perhaps 'regions' could also mean 'hell'. I am not sure about the 'lower' bit.).
'seas'+'hell'='SEASHELL'

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(Other definitions for seashell that I've seen before include "Hard remains of marine mollusc" , "periwinkle?" , "scallop?" , "Empty covering of marine mollusc" , "Case of mollusc" .)

I've seen this clue in The Times.
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