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trilobite(trī`ləbīt'), subphylum of the phylum ArthropodaArthropoda
[Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans, insects, centipedes, millipedes, spiders, scorpions, and the extinct trilobites.
..... Click the link for more information. that includes a large group of extinct marine animals that were abundant in the Paleozoic era. They represent more than half of the known fossils from the Cambrian period. The trilobite body was generally oval and flat and was divided into three roughly equal sections: the head, thorax, and tail. The name trilobite refers to a pair of furrows along the length of the animal that divided the body into three longitudinal regions. The body was covered by a mineralized shell. Because the dorsal, or upper, shell was thicker than the under shell, it has been the part best preserved in fossil form. Trilobites were abundant inhabitants of the Cambrian and Ordovician geological periods. They declined thereafter, possibly because they became food for cephalopods and later for fish, and became extinct in the Permian period. Trilobites are most closely related to the chelicerates, which include the horseshoe crabs and spiders.
See R. Fortey, Trilobite! Eyewitness to Evolution (2000).
any extinct marine arthropod of the group Trilobita, abundant in Palaeozoic times, having a segmented exoskeleton divided into three parts