Class Insecta contains twenty-six Orders of insects, each different from the next in some way. However, they all contain many similarities between each other. These include: 3 sets of legs, 1 pair of antennae, usually 1 or 2 pairs of wings, and 3 major body segments (head, abdomen, and thorax).
Insecta is divided into two subclasses. These subclasses are Apterygota and Pterygota. Apterygota includes the orders Protura, Thysanura, and Collembola, and they are wingless insects. The Pterygota have wings for the most parts, and those that don't evolved from winged ancestors.
There are several groups of animals that are similar to Insecta. These are: Arachnida, Diplopoda, and Annelida.