Arachnoid may refer to: * Relating to

arachnid Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroon ...

s *

Arachnoid (astrogeology) In astrogeology, an arachnoid is a large geological structure resembling a spider web. They are of unknown origin, and have been found only on the surface of the planet Venus. They appear as concentric ovals surrounded by a complex network of ...

, a geological structure found only on the planet Venus *

Arachnoid (botany) Arachnoid as a descriptive term in botany, refers to organs such as leaves or stems that have an external appearance similar to cobwebs from being covered with fine white hairs, usually tangled. Such material is one common cause of plants having ...

, referring to organs with a cobwebby exterior appearance *

Arachnoid granulation Arachnoid granulations (also arachnoid villi, and pacchionian granulations or bodies) are small protrusions of the arachnoid mater (the thin second layer covering the brain) into the outer membrane of the dura mater (the thick outer layer). They ...

, small protrusions of the arachnoid mater *

Arachnoid mater The arachnoid mater (or simply arachnoid) is one of the three meninges, the protective membranes that cover the brain and spinal cord. It is so named because of its resemblance to a spider web. The arachnoid mater is a derivative of the neural c ...

, a layer of the meninges, membranes that contain the central nervous system

See also