The exoskeleton is hard and it doesn't rot very fast. If there no biologist or chemistry nearby, you can imagine it's made of something similar to plastic. http

The exoskeleton is hard and it doesn't rot very fast. If there no biologist or chemistry nearby, you can imagine it's made of something similar to plastic. https://en.wikipedia.org/wiki/Arthropod_exoskeleton#Chemical_composition https://en.wikipedia.org/wiki/Arthropod_exoskeleton#Chemical... And as a sibling comment says, there is too few oxygen down there so it rots even slower.