About this curiosity:
Personnally I can't say how this luminescence can appear, under Ultraviolet light.
Or why it only happens on some Cypraeas (Mappas notably !), but to leave, however, that these Shells contain one visible early in their pink color varnish.
In the dark and under the artificial light, while shells appear to our astonished and amazed eyes of an intense red color blood !!
I suppose a certain topic, since organic component secreted by the animal to develop its polish, is to be completely sublimated during the exposure to Ultraviolet.