The fixed, false belief that one’s bodily functioning, sensation, or appearance is grossly abnormal. The somatic delusion has to do with thinking that your body is diseased in some way Sometimes these delusions include things like the idea that one’s body is completely infested with parasites (clearly untrue).
Example: A psychotically depressed man believes his internal organs have become infested with and partially consumed by large purple worms.
Here is a great website about all sorts of delusions and how to tell them apart: http://www.minddisorders.com/Br-Del/Delusions.html
Fournier, G. (2010). Somatic Delusion. Psych Central. Retrieved on February 14, 2016, from http://psychcentral.com/encyclopedia/somatic-delusion/