May be herbivores, carnivores, filter feeders or detritivores.
They have a coelom, a complete digestive system and specialised organs for excretion.
Bivalve molluscs can filter-feed fine particles from the water.
Single-shelled molluscs (limpets) possess a ribbon-shaped tongue (radula), covered with rasping teeth to scrape algae from the rock.
Whelks have a radula on a stalk that can be used to bore into the shells of other molluscs and suck out the flesh.
Cone-shells have a stalked radula which is modified into a type of harpoon with which they secure their prey before injecting it with poison.
In still more active carnivores, the heavy shell is reduced in size and may even be lost (slugs).
Sea-slugs which have an upper surface covered with tentacles.