centipedes, insects, and spiders pairwise have the arthropods as their common lineage, and spiders have 4 pairs? EDIT: but what about palps? crustaceans also c

centipedes, insects, and spiders pairwise have the arthropods as their common lineage, and spiders have 4 pairs? EDIT: but what about palps? crustaceans also can have even pairs of walking legs, but odd numbers of leg-like structures...