Arachnoid

Arachnoid is a term in anatomy for a fine delicate membrane that derived its name from arachnoides, literally 'like a cobweb' in Latin. This membrane surround the brain and spinal cord. It is the middle one of the three membranes or meninges. It lies between the dura mater and the pia mater.

Anything like a spider or arachnid is also called arachnoid.