When many types of organisms become extinct at the same time

The vast majority of species that have ever lived went extinct sometime other than during one of the great mass extinction events.

Explanation:

Since the Cambrian Explosion, there have been five mass extinctions, each of which is named for the geological period in which it occurred, or for the periods that immediately preceded and followed it. The first mass extinction is called the Ordovician-Silurian Extinction.

Explanation:

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.