Practice question

Chelicerata represents arthropod subphylum containing arachnids, merostomes and pycnogonids, united by absence of antennae and presence of chelicerae as first appendage pair. Chelicerae may be jackknife or pincer-like for grasping or fang-like injecting venom as in spiders. Lacking antennae contrasts with Mandibulata which possess antennae for sensory functions, mandibles for biting and second antennae in crustaceans. Chelicerates rely on pedipalps and leg sensory hairs for chemoreception. Antennal absence therefore serves as key diagnostic character separating chelicerates from insects, crustaceans and myriapods in systematics and evolutionary morphology.