Creature identified by duke on small low-lying island (6)
I believe the answer is:
donkey
'creature' is the definition.
(type of animal)
'duke on small low-lying island' is the wordplay.
'duke' becomes 'd' (abbreviation).
'small low lying island' becomes 'key' (I can't justify this - if you can you should give a lot more credence to this answer).
'd'+'on'+'key'='DONKEY'
'identified by' acts as a link.
Can you help me to learn more?
(Other definitions for donkey that I've seen before include "Ass; stupid person" , "- Jacket, - work" , "Garment associated with building workers" , "Domesticated animal" , "Burro" .)