How do skeleton types and temperature regulation classify animals?

When it comes to temperature regulation we can classify animals into two different groups, the endotherms, and the ectotherms.
Most mammals and birds are endotherms, which means they can alter their body temperature through their metabolic processes and be independent of the external sources of heat.
On the other sides, many reptiles are ectotherms, which means that they have to rely on external sources of heat, such as the sunlight, to maintain their body temperature

Animals also can be classified into three different groups based on the type of their skeletons. Vertebrates possess an inner skeletal system called the endoskeleton, the arthropods possess external skeleton called the exoskeleton and many soft-bodied marine animals possess hydroskeletons, bodily support systems made out of fluid-filled coelom.

The answer is one amu.