What is the defining anatomical feature of a spider's body plan, contrasting with the pond skater?

Answer

Two primary body segments: the cephalothorax and the abdomen

Spiders, belonging to Arachnida, exhibit a body divided into two main parts: the cephalothorax (a fusion of the head and thorax) and the abdomen, unlike the three-part structure of insects.

What is the defining anatomical feature of a spider's body plan, contrasting with the pond skater?
spiderinsectclassificationarachnidpond skater