One of the classes of Arthropoda. See Illustration in Appendix.
The class of invertebrates that includes spiders, scorpions, and ticks. Arachnids differ from insects in that they have only two body parts, instead of three; they have no antennae and no wings; and they have four pairs of legs, instead of three.
a large class of arthropods including spiders and ticks and scorpions and daddy longlegs; have four pairs of walking legs and no wings