An endoplasmic reticulum is rough or smooth, depending on the presence of
a. a nuclear membrane.
b. mitochondria.
c. ribosomes.
d. proteins.

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.