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| Description: The nematodes and the arthropods belong to a clade with a common ancestor, called Ecdysozoa. The name comes from the word ecdysis, which refers to the periodic shedding, or molting, of the exoskeleton. The ecdysozoan phyla have a hard cuticle covering their bodies that must be periodically shed and replaced for them to increase in size. The cuticle provides a tough, but flexible exoskeleton that protects these animals from water loss, predators and other aspects of the external environment. After molting, they secrete a new cuticle that will last until their next growth phase.The presence of an exoskeleton suggests, surprisingly, that phylum Nematoda (the roundworms) is more closely related to the Phylum Arthropoda (the arthropods) than to the other worm phyla.
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