There are over 100,000 species of amazing arachnids. The name arachnid comes from the Greek aráchnē, meaning spider. But this is more than just a group of spiders. There are 11 orders within the class arachnida, and only one of these orders, araneae, includes spiders. Explore four common types of arachnids in this study including harvestmen, spiders, scorpions and ticks.