clam-shell (n.)youdaoicibaDictYouDict
c. 1500; see clam (n.) + shell (n.). As "hinged iron box or bucket used in dredging," from 1877.
dredge (n.)youdaoicibaDictYouDict
late 15c., in Scottish dreg-boat "boat for dredging," perhaps ultimately from root of drag (possibly via Middle Dutch dregghe "drag-net"). The verb is attested from c. 1500 in Scottish. Related: Dredged; dredging.