The class Arachnida is divided into 12-13 different orders including the major groups:
- Acari (mites and ticks – often classified into a superorder and divided into two or more orders)
- Amblypygi (tailless whip scorpions)
- Araneae (spiders)
- Opiliiones (harvestmen or daddy longlegs)
- Palpigradi (micro whip scorpions)
- Pseudoscorpiones (pseudoscorpions)
- Ricinulei (hooded tick-spiders)
- Schizomida (short-tailed whip scorpions)
- Scorpiones (scorpions)
- Solifugae (camel spiders)
- Thelyphonida (whip scorpions or vinegaroons)
In addition, some recent research also places the Xiphosura (horseshoe crabs) into the class Arachnida.
The links on the left provide additional information about each of the major groups of arachnids.