(138 species)
The class Arachnida entails an enormous diversity of arthropods, the most familiar orders being spiders (Araneae) and harvestmen (order Opiliones). Ticks (Ixodida) and mites (e.g. Sarcoptiformes, Trombidiformes, among others) belong to the subclass Acari within the arachnids, where common parasitic species are placed. While the scorpions (Scorpiones) are another well-known order of arachnids, several small groups also belong to this class. Pseudoscorpions (Pseudoscorpiones) look similar to scorpions, but lack the tail that holds the toxic sting.
The remaining orders are whipscorpions (Uropygi), tailless whipscorpions (Amblypygi), short-tailed whipscorpions (Schizomida), windscorpions (Solifugae), hooked tickspiders (Ricinulei), and microscorpions (Palpigradi).
A common morphologic feature of arachnids are the four pairs of legs.
