In Arthropoda, head and thorax are often fused to form cephalothorax, but in which one of the following classes, is the body divided into head, thorax and abdomen ?

In class Insecta, the body is clearly divided into three parts: head, thorax and abdomen. The thorax bears three pairs of legs and usually two pairs of wings.
In Crustacea (e.g. prawn) and Arachnida (e.g. spider, scorpion), the head and thorax are fused to form a cephalothorax, so the body has only two parts.
In Myriapoda (centipedes, millipedes), the body has a head and a long trunk of many similar segments.
So the body is divided into head, thorax and abdomen in the class Insecta.