The spider, ticks and mites belong to the Arthropod class

The spider, ticks and mites belong to the Arthropod class Arachnida.
Arachnida is a class of joint-legged invertebrate animals, in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroons.
The term is derived from the Greek word (Arachne, 'spider'), from the myth of the hubristic human weaver Arachne, who was turned into a spider.
Adult arachnids have eight legs attached to the cephalothorax, although the frontmost pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs.