Chitin occurs in three polymorphic solid state forms designated as α, β, and γ chitin which differ in their degree of hydration, size of unit cell, and number of chitin chains per unit cell. α-Chitin is most abundant and is found in shellfish exoskeletons and fungal cell walls. β-Chitin is mainly found in squid pens and diatoms while γ-chitin may be predominantly found in squid and cuttlefish stomach lining.

Vegetal chitosan is extracted from fungal sources, it exhibits remarkable physico-chemical characteristics and can be tailored with predefined properties.
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