You can tell the difference between the five groups if you count the body parts. Body parts are called anatomy . Each group of arthropods has a different anatomy. Count the number of legs, antennae , and body sections that an arthropod has. That will tell you what group it belongs to.
Insects have six legs, two antennae, and three body sections.
That's always true. A centipede has over thirty legs, two antennae, and only two body parts. Here is a chart that shows the differences in the arthropod groups. All insects have three body sections, the head , thorax , and abdomen. Each part has its own name.