Hydrolysis of terminal non-reducing N-acetyl-D-hexosamine residues in N-acetyl-beta-D-hexosaminides. Glycan degradation; chitin degradation. Prismatic layer of shell (at protein level). Expressed primarily in the mantle with highest level in the mantle edge and lower level in the mantle pallium. Belongs to the glycosyl hydrolase 20 family. Premature stop codon at position 218.