Creature written about in Italian sonnet (5)
I believe the answer is:
snail
'creature' is the definition.
(snail is a kind of animal)
'written about in italian sonnet' is the wordplay.
'written about' says the letters should be written in reverse.
'in' indicates a hidden word.
'lians' is hidden in the letters of 'italian sonnet'.
'lians' written backwards gives 'SNAIL'.
(Other definitions for snail that I've seen before include "Slow slithery mollusc" , "Edible terrestrial mollusc" , "Mollusc with spiral shell" , "trailer" , "Slow-moving garden pest" .)