The class arachnida includes spiders (order Araneae) and scorpions (order Scorpiones). The class is part of the phylum Arthropoda, which also includes insects and crustaceans. Spiders and scorpions are characterized by having four pairs of walking legs; a pair of pincerlike mouthparts called chelicerae; another pair of frontal appendages called pedipalps, which are sensory in spiders but used for grasping in scorpions; and a body divided into two sections (a combined head and thorax called a cephalothorax or prosoma, and an abdomen or opisthosoma). Unlike other arthropods, spiders and
scorpions lack antennae. Spiders and scorpions are carnivorous. Spiders poison prey by biting with the fanged chelicerae, scorpions by stinging with the end of the metasoma (tail).
