Retrieving "Pygidium" from the archives

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1. Arthropods

   Linked via "pygidium"

   Morphology and Segmentation
   The defining characteristic of arthropods is the division of the body into distinct tagmata, or functional segments. In basal forms, such as the extinct Trilobita, the body plan included a distinct head (cephalon), thorax, and tail (pygidium). However, evolutionary pressures have led to significant fusion and specialization.
   The exoskeleton is composed primarily of chitin, of…