Creature mainly living from fir nuts collected by squirrel (8)
I believe the answer is:
starfish
'creature mainly living' is the definition.
('the main' can mean the sea)
'fir nuts collected by squirrel' is the wordplay.
'nuts' is an anagram indicator (nuts can mean crazy).
'collected by' indicates putting letters inside.
'squirrel' becomes 'stash' (I've seen this in another clue).
'fir' is an anagram of 'rfi'.
'rfi' placed within 'stash' is 'STARFISH'.
'from' is the link.
(Other definitions for starfish that I've seen before include "Asteroid (in the sea)" , "Rock pool creature with five arms" , "Astral aquatic animal" , "Heavenly marine animal?" , "Sea creature with five arms coming from central disk" .)