Chowder mollusk (4)
I believe the answer is:
clam
'chowder mollusk' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for clam that I've seen before include "ringing noise produced by > very reticent type" , "Mollusc, one proverbially reticent" , "One is as uncommunicative as a mollusc" , "Burrowing marine mollusc living in sand or mud" , "Large marine bivalve" .)