Part of tortoise arguably shell-like (3)
I believe the answer is:
ear
'shell-like' is the definition.
(I've seen this before)
'part of tortoise arguably' is the wordplay.
'part of' indicates a hidden word.
'EAR' is hidden within 'tortoise arguably'.
(Other definitions for ear that I've seen before include "one hears" , "Hearing aid?" , "Aural organ" , "Discernment musicians need" , "See 8" .)