What is the name for organisms that belong to the class Insecta and are characterized by three body regions?

The organisms that belong to the class Insecta are specifically characterized by having three distinct body regions: the head, thorax, and abdomen. This trisection is a defining feature of insects, setting them apart from other arthropods. Insects also possess other unique characteristics, such as compound eyes, antennae, and typically, six legs.

The other groups mentioned do not share this specific classification. Myriapods, for instance, include organisms like centipedes and millipedes, which have elongated bodies with numerous segments and many legs but do not conform to the three-body-region structure. Crustaceans, which include crabs and lobsters, have a different body plan with a cephalothorax and an abdomen rather than the three distinct regions found in insects. Arachnids, such as spiders and scorpions, typically have two main body segments: the cephalothorax and the abdomen, which again differs from the typical structural arrangement of insects.