Spiny lobster could be gelatinous without one (9)
I believe the answer is:
langouste
'spiny lobster' is the definition.
('langouste' can be a synonym of 'spiny lobster')
'could be gelatinous without one' is the wordplay.
'could be' indicates anagramming the letters.
'without' indicates named letters should be taken away.
'one' becomes 'i' (Roman numeral).
'gelatinous' with 'i' taken away is 'gelatnous'.
'gelatnous' with letters rearranged gives 'LANGOUSTE'.
(Other definitions for langouste that I've seen before include "something to eat" , "Sea creature" , "One in the sea" , "Seafood is possibly" , "It may be eaten roasted" .)