Possessed by lanneret, a long hooked claw (5)
I believe the answer is:
talon
'hooked claw' is the definition.
(I've seen this before)
'possessed by lanneret a long' is the wordplay.
'possessed by' indicates the answer is hidden within the clue.
'TALON' is hidden within 'lanneret a long'.
(Other definitions for talon that I've seen before include "The stock" , "Raptor's claw" , "Bird's claw" , "Eg, an eagle's claw" , "ogee moulding" .)