Four pairs of legs. Examples are spiders and scorpions.
More than four pairs of legs. Examples are shrimps, crabs, centipedes and millipedes.
Invertebrates without joined legs
This group of invertebrates includes animals which are wormlike and animals which are not wormlike.
Wormlike animals
Some of these animals have segmented bodies (ie bodies divided into segments) others do not have segmented segmented bodies.
Non wormlike animals
Some of these animals have shells others do not have shells.