What is an arachnid?

Arachnids are a class of arthropods that includes spiders, scorpions, harvestmen, ticks, and mites. Most adult arachnids have four pairs of legs, simple eyes rather than compound eyes, and bodies divided into two main sections, though some groups are less obviously segmented. They are distinct from insects, which have six legs and three main body regions. Arachnids live in many habitats on land and, in the case of some mites, in water or on other organisms. The group is ancient and has a fossil record extending hundreds of millions of years.