Shell thickening in the presence of NikkomycinZ. Scanning electron microscopy (SEM) images of shell specimens synthesized by mollusc larvae in the presence (10 μM) or absence (0 μM) of NikkomycinZ. Regions of shell thickening of 5 day old (a,b) and 19 day old (c,d) specimen are shown. Note the difference in smoothness and compactness between the 3 days (b) and 11 days (d) NikkomycinZ treated and the respective control cultures (a,c). a. The central inner surface of a 5 day old control shell reveals flakes with a homogeneous, fine-disperse granular surface structure. b. Irregular shell material agglomerated on top of the flakes (dotted lines) in NikkomycinZ treated organisms. Individual flakes bared an internal slit-like nano-scale structure (arrowheads). c. The inner surface flakes are more confluent in later developmental stages. The surface appears more compact, smooth, and homogeneous. d. After 11 days of growth in the presence of NikkomycinZ, the inner surface structure of larval shells in principle resembles the flake-like structure as observed in shells of NikkomycinZ treated younger developmental stages (b). These data suggest that the inhibition of chitin synthase influences the growth in thickness and biomineralization of larval shells on length scales of < 1 μm – 10 μm.