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Chitons are the most primitive of all living mollusks. They belong to a class called Polyplacophora (bearer of many plates). There lineage extends as far back as the late Cambrian. There are over 430 described species in the fossil record. Almost all are only known from individual body plates or valves. The Mazon Creek deposit is one of the only sites in the world where complete examples have been collected. Modern chitons have changed little from Glaphurochiton concinnus. The basic chiton body plan consists of 8 valves made of Aragonite. The front plate is named the cephalic plate and the rear plate the anal. The plates have fine ornamentation which is a key feature in differentiating species. Modern chitons can roll into a ball when threatened. The muscular body is known as the girdle. This girdle is covered with tiny spicules that are sometimes preserved on Mazon specimens. Most modern chitons use this girdle to attach themselves to rocks. To feed, the animal has a radula that can have over a hundred rows of denticles. Each row consists of 17 each. Most modern chitons attach to rocks and feed on algae. Glaphurochiton was a mud dweller feeding on detritus. Like all chitons, Glaphurochiton is strictly marine and is only found in the Essex portion of the deposit. Glaphurochiton is rare but 2 concentrations of chitons have been found. The areas have been termed “chiton hills”. It has been noted that modern chitons have a homing ability to return to there same resting spots despite lacking eyes. This first example is the largest chiton that I am aware of that has ever been found in the Mazon Creek deposit. Not including the skirt, the animal measures 70 millimeters. The typical size is usually between 30-40 millimeters.

From the mouths of molluscs -- ancient snail relative found, Physorg, August 22, 2012 http://phys.org/news...ient-snail.html Ancient Fossils Reveal How the Mollusc Got Its Teeth ScienceDaily, August 22, 2012 http://www.scienceda...20822125212.htm Odontogriphus - http://en.wikipedia.org/wiki/Odontogriphus Wiwaxia - http://en.wikipedia.org/wiki/Wiwaxia The paper is: Smith, M. R., 2012, Mouthparts of the Burgess Shale fossils Odontogriphus and Wiwaxia: implications for the ancestral molluscan radula. Proceedings of the Royal Society B: Biological Sciences. Published online before print August 22, 2012. http://rspb.royalsoc.../rspb.2012.1577 Best wishes, Paul H.