arachno-, arachn- +

(Greek: spider; the arachnoidea; when used in medicine this Greek element refers to a membrane, veins, or any web-like structure in the body)

arachnophagous (adjective) (not comparable)
Referring to the consumption of spiders: Many bird, reptiles, fish, centipedes, scorpions, and other spiders are arachnophagous animals that eat spiders!
arachnophobia, arachnephobia, arachneophobia (s) (noun); arachnophobias, arachnephobias, arachneophobias (pl)
An excessive fear of spiders: Many people suffer from the dread of experiencing arachnephobia, especially when seeing a tarantula or black widow in their homes!
Scribe is frightened by the shadow of a spider
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Spiders, Spiders Everywhere

Currently, about 30,000 species of spiders have been recognized, although it is certain that many more have yet to be discovered in all parts of the world.

The spiders are known to occupy nearly every terrestrial habitat, from the peaks of the highest mountain ranges into the depth of the largest caves and holes, from damp marshes to dry deserts. Anywhere in fact that they can find other arthropods to provide them with meals.

—Rod & Ken Preston-Mafham Spiders of the World
arachnopia (s) (noun), arachnopias (pl)
Now known as "leptomeninges" which are the two innermost layers of tissues that cover the brain and spinal cord: The arachnopias are called the arachnoid mater and pia mater (the delicate innermost membranes enveloping the brain and spinal cord).

piarachnoid (s) (noun) (no pl)
The two delicate layers of the meninges: The arachnoid mater and pia mater, considered as one unit, comprise the piarachnoid.
spider (s) (noun), spiders (pl)
1. A predatory invertebrate creature of the order Araneae: A spider has four pairs of legs and two or more abdominal spinnerets used for spinning webs that serve as nests and traps for prey.

A spider is popularly thought to be an insect, although it is an arachnid of the order Araneae.

2. A computer program that searches the internet for newly accessible information to be added to the index examined by a standard search tool: When Jack bought his new computer, he made sure that it had a spider in order to gather new facts and knowledge for his classes at school.

Spiders are every where in abundance

Currently, about 30,000 species of spiders have been recognized, although it is certain that many more have yet to be discovered from all parts of the world.

Spiders are known to occupy nearly every terrestrial habitat, from the peaks of the highest mountain ranges to the depths of the largest caves and pot-holes; from damp marsh to dry desert, anywhere in fact that they can find other arthropods to provide them with a meal.

Some spend at least part of their lives running around on the surface of the freshwater lakes and ponds and a few of these can dive to safety and survive below the surface of the water for a short time, although only the true water spider, Argyroneta, has perfected this ability to the extent that it is able to live a wholly aquatic existence.

All spiders are carnivorous and feed almost exclusively on prey which they have caught for themselves, although a few species take advantage of food which has been taken by other spiders and one family feeds exclusively on other spiders.

Although many species of spiders have a fairly wide distribution both within and between the continents of the world, the majority tend to be found within a fairly restricted habitat because they are specifically adapted to live in that particular area.

A spider adapted for living in a damp, marshy habitat, for example, would find it impossible to live in the hot, dry conditions that exist within deserts.

Spiders of the World by Rod & Ken Preston-Mafham;
Facts On File Publication; New York; 1984; page 11.
subarachnoid, subarachnoidal (adjective) (not comparable)
Regarding the place beneath the arachnoid, the middle of three membranes that cover the central nervous system.

In practice, subarachnoid usually refers to the space between the arachnoid and the pia mater, the innermost membrane surrounding the central nervous system.

The subarachnoid space normally contains cerebrospinal fluid. A subarachnoid hemorrhage is a bleeding into this space.

The arachnoid is named for its delicate, spider-web-like filaments that extend from its undersurface through the cerebrospinal fluid in the subarachnoid space to the pia mater (delicate and highly vascular membrane immediately covering, or enveloping, the brain and spinal cord).

subarachoidean (adjective) (not comparable)
A reference to being situated under the arachnoid membrane: Beneath the arachnoid is the subarachoidean part containing the cerebrospinal fluid, which acts as a soft support and is important for protecting the brain.

Cross references of word families that are related directly, or indirectly, to: "spider; arachnoidea": acaro-; arano-; mite, mites.