To make this image, I photographed two split halves of a Nautilus shell on a mirror placed on a black velvet background. I lit the composition using natural light and a silver metallic reflector. The wonderful bright and luminescent quality of the shell in contrast to the black background is partly due to the lens I used, my Zeiss Otus 1.4/55mm.
I really enjoy photographing shells with spirals, such as this image of my Nautilus in Black and White and this Architectonica. If shell spirals intrigue you, also check out this playful version, Spirals!