Spiny creature aunt ogles in unseemly fashion (9)
I believe the answer is:
langouste
'spiny creature' is the definition.
'aunt ogles in unseemly fashion' is the wordplay.
'in unseemly fashion' is an anagram indicator.
'aunt'+'ogles'='auntogles'
'auntogles' anagrammed gives 'LANGOUSTE'.
(Other definitions for langouste that I've seen before include "Seafood is possibly" , "something to eat" , "Sea creature" , "It may be eaten roasted" , "Swimmer" .)