With three pairs of legs. Often with wings insects
N.B. Newly hatched mites also have three pairs of legs, but they are extremely small, under 1 mm.
With four pairs of legs spiders, mites, scorpions etc.
With more than four pairs of legs.
It may be a slug slugs
It may be a worm worms.
It may be a maggot-like insect larva insect larvae.
With three pairs of true legs, and prolegs on abdomen certain insect larvae.
With 7 pairs of legs woodlice.
With many legs, more than 14 pairs
Flat animals, legs protruding laterally centipedes.
Cylindrical animals, legs attached ventrally millipedes.