Mutualism is a type of relationship in which:
one organism is and the other is neither nor harmed
one organism is and the other is harmed < --i think this one
both organisms benefit
neither organism benefits

one characteristic that is shared by all is a soft body. many

of these invertebrate animals also have an outer shell to protect their

body. oysters, clams, snails, and mussels are all mollusks. so are octopuses, squids, and slugs. mollusks live on land and in freshwater.