one of many classes of Arthropoda See Illustration in Appendix
- a large course of arthropods including spiders and ticks and scorpions and daddy longlegs; have actually four pairs of walking feet with no wings
- among courses of Arthropoda. See Example in Appendix.
The Arachnida are divisible into two grades of structure - according to the fixity or non-fixity of the number of somites building up the body: - Grade A (of the Arachnida).