trilobite (trī`ləbīt'), subphylum of the phylum Arthropoda Arthropoda (ärthrŏp`ədə) [Gr.,=jointed feet], largest and most diverse animal phylum.
..... 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.
Any of a group of ovate arthropods (subphylum Trilobita) that came to dominate the seas c. 540 million years ago and became extinct c. 245 million years ago. Trilobites had a chitinous exoskeleton and three body lobes: a raised middle lobe with a lower lobe on each side. The head, thorax, and tail were segmented; each segment bore two appendages. The forwardmost appendages were sense and feeding organs. Most species had two compound eyes, though some were eyeless. Some were predators, others were scavengers, and still others probably ate plankton. Paradoxides harlani, found near Boston, grew to 18 in. (45 cm) long and may have weighed 10 lbs (4.5 kg). Other species were small.
trilobite
..... 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.
Bibliography
See R. Fortey, Trilobite! Eyewitness to Evolution (2000).
trilobite
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Trilobite
(credit: Leslie Jackman—Natural History Photographic Agency)
trilobite
any extinct marine arthropod of the group Trilobita, abundant in Palaeozoic times, having a segmented exoskeleton divided into three parts
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