Silly story about English mollusc (6)
I believe the answer is:
oyster
'mollusc' is the definition.
(oyster is a kind of mollusc)
'silly story about english' is the wordplay.
'silly' is an anagram indicator.
'about' indicates putting letters inside.
'english' becomes 'E' (abbreviation).
'story' anagrammed gives 'oystr'.
'oystr' going around 'e' is 'OYSTER'.
(Other definitions for oyster that I've seen before include "Capital card" , "Bivalve native" , "It produces pearls" , "very uncommunicative person" , "Storey (anag)" .)