Selenizone

It is a spiral band of crescentric growth lines or threads (lunulae) on the shell surface due to the semicircular end of a notch or slit on the outer lip.

It has also been suggested that the selenizone may serve to reinforce the shell against catastrophic breakage during predation attempts.

[2] A new shell-morphological term 'sutsel' has been introduced by Dr. Geiger for the area between the SUTure and the SELenizone.

In the Haliotidae, the abalone, the selenizone takes the form of a series of holes in the shell (reaching back from the leading growth edge of the aperture) which form as the shell grows.

[4] A list of superfamilies and families (both living and fossil) which show this structure, based on the taxonomy of Bouchet et al 2005.

Four view of the slit shell Mikadotrochus hirasei . The first view shows the selenizone well. The other views show its relationship to the slit in the shell.
Three artificially polished shells of a New Zealand abalone , a Haliotis species, probably H. iris . The central shell clearly shows the selenizone as a series of holes