Chelicerates (Arachnids - including spiders, scorpions, pseudoscorpions harvestmen, ticks and mites)

Arachnids have a head which is fused to their thorax forming a cephalothorax. The cephalothorax has sensory organs, mouthparts, limbs and stomach. The remaining body segments are fused to form an abdomen. The abdomen contains the heart, lungs, gut, reproductive organs and anus. This means that the body of an arachnid is only divided into 2 sections whereas insects have 3 body sections.
Arachnids use their sensory hairs, sensory organs and simple eyes to detect and analyse their surroundings. Arachnids are cold-blooded animals that get warmth from their environment.
Arachnids are diverse in size ranging from a few millimetres to 20 centimetres in length. They have a strong exoskeleton made of calcium and carbohydrates which protects them from predators. Arachnids do not possess teeth and most cannot digest solid foods, this is why they suck fluids from their preys body.
A scorpion has a tail that extends from their abdomen bearing a painful stinger on the end. At the front are 2 pincer-like chelicerae which are used to consume prey and a pair of limb-like pedipalps. They have 4 pairs of walking legs. Psuedoscorpions are not really scorpions although they have a similar appearance.
Pseudoscorpions do not have the extended tail with the stinging end, instead they produce venom from their pincer-like pedipalps. Pseudoscorpions also produce silk from silk glands which are located on the jaws or chelicerae. The silk is used to construct cocoons in which they molt and live during the winter. They usually range from 2 to 8 millimetres in length. The largest known species is Garypus titanius of Ascension Island at up to 12 millimetres.
Ticks are parasites that feed upon the blood of mammals such as humans, dogs, cows and sheep. Ticks are tiny arachnids, about the size of a grain of rice. They climb onto their host, gripping tightly with their legs and feed by sinking their mouthparts into the hosts skin and gorges itself on blood. Once the ticks body is full, it swells like a tiny balloon and falls off its host.
Most spiders are predatory arachnids that inject venom to catch their prey. Some spiders spin webs in order to catch their prey, others like the Brazilian Wandering spider walks the jungle floors in search of prey instead of residing in a lair or maintaining a web.