Removing the uncertainty of chitin structure in chitons (Mollusca: Polyplacophora: Chitonida)

Chitons, also known as "living fossils", have been proposed as one of the earliest differentiated groups of molluscs. Although Polyplacophora is an ancient group of molluscs, very few studies have been conducted on the chitin of these organisms compared tobivalves, gastropods and cephalopods. The few available studies have provided contradictory results regarding the present chitin types, depending on the examined body parts. Herein, to solve this controversy, we studied the chitin from valve, girdle and radula of a chiton species by protecting the 3D structure of the body parts. Results obtained using infrared spectroscopy and Thermogravimetric analysis clearly showed chitons contain β-chitin in the girdle and valve; however, the signal detected for the type of chitin contained in the chiton radula appears to be α-chitin. In addition, chitin content of the whole chiton body on dry basis was recorded as 22.78%.