Nemo's sub in USA, until wrecked (8)
I believe the answer is:
nautilus
'nemo's sub' is the definition.
(I've seen this in another clue)
'usa until wrecked' is the wordplay.
'wrecked' is an anagram indicator.
'usa'+'until'='usauntil'
'usauntil' with letters rearranged gives 'NAUTILUS'.
'in' acts as a link.
(Other definitions for nautilus that I've seen before include "Spiral-shelled mollusc" , "Mollusc and first nuclear-powered submarine" , "Sea creature - literary submarine" , "Sea creature to be found in the usual tin, unusually" , "Cephalopod mollusc" .)