Answer
The animals of the subphylum Chelicerata includes, spiders, scorpions, ticks, mites, harvestmen etc. They have no mandibles or antennae. But they have six pairs of other appendages: one pair of chelicerae; one pair of pedipalps, and four pairs of walking legs.
Chelicerae may vary in detailed structure among subgroups of Chelicerata, but in general, chelicerae are modified for blood feeding. In certain spiders, the chelicerae end like fangs, have muscles, and associated poison glands. These spiders attack prey and immobilize them by injecting venom into them. The muscles on the chelicerae enable the spiders to hold the pray while the venom is being injected. The spiders proceed to tear the flesh of their victims with the claw-like or fang-like ends of the chelicerae, then they pour digestive juices into the torn flesh and suck up the nourishing liquid.
Scorpions have chelicerae that function like scissors . They are the most anterior appendages
Pedipalps have six segments; they usually function as sensory organs of touch, but may serve feeding, prehensile, and secondary sexual purposes.
. The most posterior appendages are the four pairs of "walking" legs The function of the four pairs of "walking legs" is ostensibly locomotion, but their usages varies from group to group: the first pair may function as tactile and/or secondary sexual organs .
Work Step by Step
Just as the chelicerae may vary in structure and function, so too may the pedipalps and four pairs of "walking" legs.
In some spiders, pedipalps serve as chemical detectors, and as secondary sexual / copulatory organs. The first and second pairs of walking legs may also be modified to serve copulatory and other functions in some groups of the Chelicerata
