Largest Phylum
Unique Characteristics: Exoskeleton, paired jointed appendages, segmentation, open circulatory system, ventral nerve cord, classified based on number and structure of body segments and appendages.
Examples: Centipedes and millipedes, obvious segmentation
crustaceans, two body regions, cephalothorax
arachnids, no antennae, simple eyes
insects, first animal to develop flight
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