Chelicerates are a group of arthropods that include spiders, scorpions, ticks, and horseshoe crabs. They are characterized by having chelicerae, which are specialized mouthparts used for feeding. Unlike insects, chelicerates do not have antennae and typically have two main body segments: the cephalothorax and the abdomen. This diverse group is primarily divided into two main classes: Arachnida, which includes spiders and scorpions, and Merostomata, which includes horseshoe crabs. Chelicerates play important roles in ecosystems, often serving as predators or parasites, and they have adapted to a wide range of environments, from deserts to oceans.