As a temperate species, the Chestnut Cowry (Neobernaya spadicea) is not suitable for tropical systems. Though they do quite well in cold-water tanks. They are carnivores and will resort to scavenging. They feed upon many things such as sponge, ascidians, anemones, and cup coral.
Although there are many species, few are available within the aquarium trade. In my opinion, the best cowries for tropical reef systems are the small herbivores, such as Erosaria moneta and Erosaria annulus. And they are quite lovely. They are somewhat susceptable to predation, especially by crabs.
There are a fair number of omnivorous cowries that may do well in a tank, such as Cypraea tigris and Mauritia arabica. But they can present a few problems, depending on what else is living in your system. Tigers will certainly take nips at your coral. Arabian cowries may take nips at your anemones. Tigers do get large and have a tendancy to rearrange live rock. Arabians will do this to a lesser extent.
A rarely mentioned problem with larger species is that when stressed they may generate a copious amount of transparent, gooey slime. Sorry to be gross but, really, it is just like snot. If you encounter this, remove this stuff immediately as it can smother gills and suffocate fish.
Cheers,
Bob