Primary succession
a. is caused solely by human events
b. occurs on preexisting soil
c. occurs in areas without soil
d. becomes normalized by climax species

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.