Heard inside the shell-like (3)
I believe the answer is:
ear
'shell-like' is the definition.
(I've seen this before)
'heard inside' is the wordplay.
'inside' indicates a hidden word.
'EAR' is hidden within 'heard'.
'the' acts as a link.
(Other definitions for ear that I've seen before include "Sensory organ" , "Heed" , "Ability to recognise sounds" , "Part of a cereal plant containing the seeds" , "Sense organ" .)