The molluscs, the snails and their relatives make a natural group, based on their body plan and general anatomy and their mode of reproduction.
Snails live in water and on land, and even in the most unlikely places, including a number of deserts. Some snails are very efficient at conserving water.
Some snails eat plants, grinding tissue with a radula, while others are carnivorous. Tropical cone shells are dangerously venomous, hunting and catching prey.
Normal shelled snails can be found with both right-handed (normal thread) and left-handed (reverse or gas thread) shells. Most species have just one form.
Snails can be cultivated fairly easily, and are worth careful observation for their methods of eating and locomotion, as seen when they move across glass.
Slugs are shell-less snails with a somewhat different body plan, but they also possess asymmetrical arrangements left over from when they had shells.
Octopuses are highly intelligent, and can be trained to perform a variety of complex tricks. They will also solve problems involving travelling through mazes.
Some octopuses lay out items on the sandy sea floor in a pattern that probably assist them in finding the way back to their shelter when danger threatens.
Some octopuses, particularly the blue-ringed octopus, carry a powerful toxin that can kill humans. This is tetrodotoxin, which they probably get from microbes.