General Description
Arachnids (Class Arachnida) are invertebrate animals in the Phylum Arthropoda that have an exoskeleton, a two-part segmented body, and eight jointed legs. The body is divided into the prosoma (cephalothorax) and the opisthosoma (abdomen). The prosoma contains the mouth and acts as the site of attachment for the chelicerae (mouthparts), pedipalps (variously modified appendages), and four pairs of legs and associated musculature. It also contains the brain (neural ganglia), pharynx, stomach, and eyes (when present). The opisthosoma contains most of the organs of the digestive, circulatory, reproductive, and respiratory systems including the midgut, heart, ovaries or testes, and book lungs. They are ectothermic (cold-blooded).
The Class Arachnida contains the following orders:
Araneae: True Spiders, Tarantulas, Trapdoor Spiders
Thelyphonida: Whip Scorpions, Vinegaroons
Amblypygi: Tailless Whip Scorpions
Solifugae: Sun Spiders, Wind Scorpions, Camel Spiders
Opiliones: Harvestmen, "Daddy Longlegs"
Schizomida: Whip Scorpions with divided exoskeletons
Acari: Ticks and Mites
Palpigradi: Micro Whip Scorpions
Ricinulei: Hooded Tickspiders
 Arachnids as Pets
Arachnids are gaining in popularity and availability as pets. Many are low maintenance and inexpensive to keep. Many can be captured around the house or yard, depending on location, while a growing assortment of native and exotic arachnids can be found at many local pet stores. Most of the arachnids kept as pets come from the orders in bold print the above section. Occasionally, someone will capture and attempt to keep species from some other orders (especially Solifugae) with limited success. On the other hand, mites from Order Acari can become a very difficult pest to exterminate from an owner's prized collection of tarantulas and scorpions.