the fossil record is uncharacteristic of benthic animals, suggesting a pelagic existence. The thoracic segment appears to form a hinge between the head and pygidium allowing for a bivalved ostracodan-type lifestyle. The orientation of the thoracic appendages appears ill-suited for benthic living. Recent work suggests that some agnostids were benthic predators, engaging in cannibalism and possibly pack-hunting behavior. They are sometimes preserved within the voids of other organisms, for instance within empty hyolith conchs, within sponges, worm tubes and under the carapaces of bivalved arthropods, presumably in order to hide from predators or strong storm currents; or maybe whilst scavenging for food. In the case of the tapering worm tubes Selkirkia, trilobites are always found with their heads directed towards the opening of the tube, suggesting that they reversed in; the absence of any moulted carapaces suggests that moulting was not their primary reason for seeking shelter. References External links Order Agnostida by Sam Gon III. The Virtual Fossil Museum – Trilobite Order Agnostida Agnostida fact sheet by Sam Gon III. "Earth's Early Cannibals Caught in the Act", by Larry O'Hanlon, news.discovery.com. Trilobite orders Cambrian trilobites Ordovician trilobites Fossil taxa described in 1864 Cambrian first appearances Late Ordovician extinctions Taxa named by John William Salter