Chelicerates have appendages called pedipalps, which aid in reproduction and feeding. Scorpians were the first group, but spiders are the most common, with 30,000 species. Crustaceans Inlcudes Crayfish, Crabs and Shrimp. They usually have compound eyes with multiple lenses. Creyfish have mandibles, used for feeding.
Insects have mandibles, un-branched appendages, and highly specialized mouthparts.