Simplify the following text for a Grade 10 native English-speaking person.
Original: Edible cephalopods such as squid , octopus , and cuttlefish and terrestrial snails , though all molluscs , are sometimes considered to be shellfish and sometimes not .
Simplified: Cephalopods ( squid , octopus , cuttlefish ) and bivalves ( clams , oysters ) are molluscs , as are snails and slugs .