<p>A, Hyolithid specimen with three-dimensionally preserved digestive tract from Cambrian Stage 4 of northern Canada, reprinted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088583#pone.0088583-Butterfield2" target="_blank">[30]</a> under a CC BY license, with permission from Oxford University Press, original copyright 2003, and reconstruction of the simple U-shaped hyolithid digestive system. B, Specimen of the orthothecid <i>Girvanolithes thraivensis </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088583#pone.0088583-CowperReed1" target="_blank">[75]</a> with three-dimensionally preserved digestive tract from the upper Ashgill of the Girvan district, Scotland, reprinted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0088583#pone.0088583-Malinky3" target="_blank">[33]</a> under a CC BY license, with permission from Paleontological Society original copyright 2003, and reconstruction of the partially folded U-shaped orthothecid digestive system.</p
