Woodlice, crabs, shrimps and lobsters are all crustaceans. They have a hard exoskeleton and seven or more pairs of legs but no wings. Lots of crustaceans live in water. Woodlice do not live in water but need a dark, damp habitat to prevent their exoskeleton from drying out.
Myriapod means 'many-legged one'. Centipedes and millipedes are myriapods. They can have anything between about 10 and 200 pairs of legs. Most of them live in dark, damp places like in soil, dead leaves, or under stones and wood. Some myriapods are so tiny you need a microscope to see them whereas others can be 30cm long!
Centipedes have lots of segments to their body and each segment has one pair of legs attached to it. Millipedes have two pairs of legs to each body segment.
Centipedes are predators but millipedes are vegetarians.
Snails, shellfish, octopus and slugs are all molluscs. Many molluscs live in water and some have shells but none have wings.