Final answer:
The primary function of chelicerae in arthropods is as specialized mouthparts used for feeding and defense, which may include venomous fangs in spiders and gripping appendages in scorpions.
Step-by-step explanation:
The primary function of chelicerae in arthropods, specifically within the subphylum Chelicerata, is to serve as specialized mouthparts for feeding and defense. Chelicerae, which are modified first pair of appendages, are used for grasping prey in many chelicerates like scorpions, and in the case of spiders, they are often equipped with fangs that can inject venom into their prey. In addition to feeding, chelicerae may also have roles in locomotion, as seen with aquatic versions, or in reproductive processes, as is the case with male sea spiders that use a similar appendage known as ovigers to carry eggs.
Instead of mandibles, which are found in other arthropod groups like insects and crustaceans, chelicerates have evolved chelicerae and pedipalps to carry out the tasks of manipulating and sensing their environment. The prosoma, or cephalothorax, houses the chelicerae and helps in forming a preoral cavity, which is used by many chelicerates to ingest food, sometimes pre-digesting it with secreted enzymes. It's worth noting that terrestrial chelicerates, such as spiders, have adapted internal breathing systems such as tracheae or book lungs to cope with life on land.