You can sort arthropods into four main categories: chelicerates, crustaceans, hexapods, and myriapods. (All are magnificent.)
ALT Chelicerates identification guide with photos of spiders, scorpions, ticks, and mites. Key features: 8 legs, no antennae, two body segments
ALT Crustaceans identification guide with photos of crabs, lobsters, shrimp, and isopods. Key features: two pairs of antennae, 5 pairs of legs, often aquatic
ALT Hexapods identification guide with photos of various insects. Key features: 6 legs, three body segments, one pair of antennae, most have wings
ALT Myriapods identification guide with photos of centipedes and millipedes. Key features: many body segments, 1-2 pairs of legs per segment