A class of chelicerate arthropods that includes spiders, scorpions, mites, and ticks. They have become adapted for a terrestrial life and possess book lungs and tracheae, and many have silk or poison glands.
- The Arachnida include the terrestrial chelicerates that everyone is familiar with, and that nearly everyone would rather not be too familiar with: spiders, ticks and mites, and scorpions (Scorpiones).
- Ticks belong to the class Arachnida, which counts mites, spiders and scorpions among its members.
- However, they were not true spiders, nor necessarily ancestral to them, but represented independent offshoots of the Arachnida.
Modern Latin (plural), from Greek arakhnē 'spider'.
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