What are the four subgroups after the arthropods?

Answer 1

Under the arthropoda phylum are subphyla Chelicerata, Myriapoda, Crustacea, and Hexapoda. (There is also an extinct class Marrellomorpha and an the extinct Trilobite subphylum). The chelicerata include Spiders, scorpions, mites, etc. Myriapods include centipedes and millipedes. Crustaceans include lobsters, krill, crabs, shrimp, woodlice, etc. Hexapoda include the class Insecta, the insects.

Answer 2

Under the arthropoda phylum are subphyla Chelicerata, Myriapoda, Crustacea, and Hexapoda. There is also an the extinct Trilobite subphylum (and an extinct class Marrellomorpha). The chelicerata include spiders, scorpions, mites, etc. Myriapods include centipedes and millipedes. Crustaceans include lobsters, krill, crabs, shrimp, woodlice, etc. Hexapoda include the class Insecta, the insects.

Note that taxonomy is a somewhat fluid science with groups, levels, ranking subject to debate; some texts specify subgrouping slightly differently, or may show a subphylum as a superclass or class, etc.