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Class Arachnida encompasses a diverse group of arthropods commonly known as arachnids, characterized by their distinctive body structure with two main segments, the cephalothorax and the abdomen. This class includes animals such as spiders, scorpions, mites, and ticks, as well as lesser-known groups like pseudoscorpions. These creatures are typically terrestrial and exhibit a variety of lifestyles, from free-living predators to parasites. They possess four pairs of legs, lack antennae, and have simple eyes or none at all. The class Arachnida is defined by unique features such as specialized mouthparts called chelicerae, pedipalps that serve various functions including feeding and mating, and book lungs or tracheae for respiration.