Sugar found in bone and lobster (occasionally) (6)
I believe the answer is:
ribose
'sugar' is the definition.
(I know that ribose is a type of sugar)
'bone and lobster occasionally' is the wordplay.
'bone' becomes 'rib' (rib is a type of bone).
'and' is a charade indicator (letters next to each other).
'occasionally' indicates alternate letters (letters taken at regular intervals or occasions).
The alternate letters of 'lobster' are 'ose'.
'rib'+'ose'='RIBOSE'
'found in' is the link.
(Another definition for ribose that I've seen is " Kind of sugar - be or is (anag)".)