A-rāch'ni-dā, n. pl.

n. pl. (Zoöl.) The class of spiders. See ANIMAL KINGDOM.

Like the insects, and unlike the crustacea, they are air-breathing; but like the crustacea, and unlike the insects, they have no distinction of head and thorax, the two being united into what is called a cephalo-thorax. They undergo no metamorphosis, and have no antennae, and no wings. The order includes, with spiders, the scorpions, and mites, or acari.

Dana.

Mygale fod'iens.