Assertion: whelk's foot | /r/MadeOf | tough material
Facets:
value: very
type: DEGREE
Source sentences:
text: Body parts are often hidden as the snail withdraws into its shell and closes it's aperture with a 'trap door' called an operculum, a dark plate carried on top of the foot made of very tough material that protects the snail's body when retracted into the shell.