Practice question

Phylum Arthropoda is defined by presence of paired jointed appendages composed of articulated podomeres moved by antagonistic striated muscles inserting on exoskeleton interior, allowing precise flexion and extension. Body is segmented and tagmatized into functional regions, appendages specialized into sensory antennae, feeding mandibles, maxillae, chelicerae and walking legs. Such jointed limbs contrast with unjointed parapodia of annelids, muscular foot of molluscs and hydraulic tube feet of echinoderms. Distal-less gene patterning controls limb outgrowth. Jointed appendage architecture underpins arthropod evolutionary radiation, enabling terrestrial locomotion, flight, burrowing and manipulation unparalleled among invertebrates.