In the mallee, chanced to see an annelid worm (5)
I believe the answer is:
leech
'an annelid worm' is the definition.
(leech is a kind of annelid worm)
'in the mallee chanced to' is the wordplay.
'in' says the answer is hidden in the clue.
'LEECH' is hidden in the letters of 'mallee chanced to'.
'see' is the link.
(Other definitions for leech that I've seen before include "and one of his remedies" , "Small worm once used for blood-letting, or a parasitical person" , "Blood-sucking worm or parasitic person" , "Annelid worm, used in medicine of old" , "Old medicinal sucker" .)