Arachnids have eight legs, scissors-like mouthparts (chelicerae), arm-like

appendages (pedipalps), book-lungs or tracheae for breathing, and 

usually a two-part body plan (prosoma and opisthosoma). Nearly all are

predators except some harvestmen, which scavenge, and many mites

and ticks, which are parasitic or even plant feeders. Many mites are free-

living, however.

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