Chitin is a linear polysaccharide composed of repeating β(1,4)-N-acetyl-D-glucosamine units. As the second most abundant natural polysaccharide, chitin is known as the primary component of fungi cell wall, it also present in marine invertebrates, insects, and can be produced by bacteria.
References
Hofmann, A. (1929). Über den enzymatischen Abbau des Chitins und Chitosans [On the enzymatic degradation of chitin and chitosan] (Thesis). Zurich, Switzerland: University of Zurich. Matyjaszewski, K., Möller, M., Schmidt, H., & Ueda, M. (2012). Polymer science: a comprehensive reference. Elsevier.