What are the major groups of arthropods?

The phylum Arthopoda is divided among four extant subphyla:

• Chelicerata: spiders, scorpions, ticks, mites, horseshoe crabs, and sea spiders.
• Crustacea: crabs, shrimp, krill, lobsters, copepods, and barnacles.
• Myriapoda: centipedes, millipedes, symphylids, and pauropods.
• Hexapoda: insects

Additionally, the extinct subphylum Trilobitomorpha consisted of trilobites, which were dominant in early Paleozoic seas.