How are insects (Class Insecta) primarily distinguished from other arthropods like arachnids?

Answer

By having a body divided into three distinct sections and possessing three pairs of legs

Insects are distinguished from other arthropods primarily by having a body divided into three distinct sections (head, thorax, abdomen) and possessing exactly three pairs of legs attached to the thorax.

How are insects (Class Insecta) primarily distinguished from other arthropods like arachnids?
taxonomyanimalinsectclassificationmoth