Muscular System:
All mollusks have a foot that allows them to do different tasks.
Gastropods:
Gastropod’s have their foot at the their ventral side which allows them to move around. Their foot is also able to be retracted through a retractor muscle.
Bivalvia:
Clams use their feet to dig into the ground. It can be located inside their shells.
Cephalopoda:
For squids and octupus’ , their foot are at the ends of their 2 tentacles. They are able to squeeze through any hole or crevice as long as it’s larger than their beak.
Skeletal System:
Mollusks skeleton are practically their shell which is made out of calcium carbonate. Their shells can be those shells on snails or the 2-part shells of clams.
Cephalopods instead have an internal skeletal structure called “a pen” which helps them to keep their shape. This is only found on cuttlefish and squid.
A Study In Biology 