Arachnid is on crop unfortunately (8)
I believe the answer is:
scorpion
'arachnid' is the definition.
(scorpion is a kind of arachnid)
'is on crop unfortunately' is the wordplay.
'unfortunately' indicates an anagram.
'is'+'on'+'crop'='isoncrop'
'isoncrop' with letters rearranged gives 'SCORPION'.
(Other definitions for scorpion that I've seen before include "Small spider with pincers and stinging tail" , "Stinging arachnid - constellation" , "Venomous creature" , "Arachnid with venomous sting" , "can sting one" .)