Exoskeleton and Skeletal system

Exoskeleton noun - The exterior protective or supporting structure or shell of many animals (especially invertebrates) including bony or horny parts such as nails or scales or hoofs.

Skeletal system and exoskeleton are semantically related. In some cases you can use "Skeletal system" instead a noun "Exoskeleton".

Skeletal system noun - The hard structure (bones and cartilages) that provides a frame for the body of an animal.

Exoskeleton and skeletal system are semantically related. Sometimes you can replace term "Exoskeleton" with "Skeletal system", this terms are similar.