Start to bite one tube mollusc (7)

I believe the answer is:

bivalve

I'm a little stuck... Click here to teach me more about this clue!

'mollusc' is the definition.
(I know that bivalve is a type of mollusc)

'start to bite one tube' is the wordplay.
'start to' indicates taking the first letters.
'one' becomes 'i' (Roman numeral).
'tube' becomes 'valve' (I can't explain this - if you can you should believe this answer much more).
The initial letter of 'bite' is 'b'.
'b'+'i'+'valve'='BIVALVE'

Can you help me to learn more?

(Other definitions for bivalve that I've seen before include "Shellfish with hinged double shell" , "Mollusc with two shells" , "Eg, oyster or mussel" , "Oyster, perhaps" .)

I've seen this clue in the Sydney Morning Herald.

Want a hint initially instead of a full solution? Install my app