Final answer:
Arthropods are characterized by a segmented body, hard exoskeleton, and jointed appendages. Subgroups exhibit unique synapomorphies: Chelicerata have chelicerae, Myriapoda feature numerous legs, Crustacea possess two pairs of antennae and biramous appendages, and Hexapoda are defined by three pairs of legs and often two pairs of wings.
Step-by-step explanation:
Synapomorphies of Arthropod Subgroups
Arthropods are a highly diverse group of organisms characterized by common features such as a segmented body, hard exoskeleton, and jointed appendages. This general body plan has been modified in various ways across different arthropod subgroups to give rise to specific synapomorphies.
The subphyla Chelicerata includes organisms such as spiders, mites, and scorpions. This group is characterized by their chelicerae, which are specialized appendages used for feeding and defense, and by having bodies divided into two tagmata: the cephalothorax and the abdomen. They also typically have six pairs of appendages.
Myriapoda, which includes centipedes and millipedes, is known for having numerous body segments with one or two pairs of legs per segment, depending on the class, and a single pair of antennae.
The Crustacea subphylum, comprising crabs, lobsters, and shrimp, among others, often features two pairs of antennae, mandibles for feeding, and biramous appendages, which have both endopods and exopods.
Lastly, Hexapoda, primarily made up of insects, is distinguished by having three pairs of legs and usually two pairs of wings, a body divided into head, thorax, and abdomen, and uniramous appendages.