Outer surfaces of larval shell edges synthesized 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. Shell edges of 8 day old (a,b) and 19 day old (d,f), and 22 day old (c,e) specimen are shown. Note the difference in smoothness and compactness between the 3 days (b) and 11 days (d,f) NikkomycinZ treated cultures, and the respective control cultures (a,c,e). a. In control cultures, the prodissoconch II shows regular growth lines (arrowheads) and a smooth shell rim. b. Three days of NikkomycinZ treatment produced irregular shell edges in eight day old larvae. Defined growth lines are not present. The inset shows a close-up view of the irregular, porous surface texture. c. The shell edge of a 22 day old control larva consists of globular elements. The globules are embedded within a homogeneous layer in the previously formed shell parts (arrowheads). d. The outer surface has a porous appearance (black arrowheads) in 19 day old shells formed for 11 days in the presence of NikkomycinZ. The homogenous shell surface layer is not as distinct as observed in control cultures (compare white arrowheads in (c) and (d)). e. A higher magnification image of (c) shows in detail the transition region between the shell rim and the outer surface region covered by the homogeneous layer. f. Image of the specimen described in (d) at the same scale and at a comparable shell position as the control (e). Note the differences in the texture and porosity of the surface layer. These data suggest that the inhibition of chitin synthase influences the outer shell cover and biomineralization of larval shells on length scales of < 1 μm – 10 μm.