Shellfish offering you something that's eaten raw for starters (6)
I believe the answer is:
oyster
'shellfish' is the definition.
(I know that oyster is a type of bivalve)
'offering you something that's eaten raw for starters' is the wordplay.
'for starters' says to take the initial letters.
The initial letters of 'offering you something that eaten raw' is 'OYSTER'.
(Other definitions for oyster that I've seen before include "Shellfish - colour" , "Pearl-yielding shellfish" , "Storey (anag)" , "Pearl-producing bivalve" , "One eaten by Walrus and Carpenter" .)