Many insects can also see in the ultraviolet range, and many flowers have
intricate patterns and colors that are visible only by UV.  Therefore
insects (and perhaps birds, from what Sylvia said) can see these patterns,
while we cannot. I don't know of any research on UV perception in molluscs,
so all I can offer is an opinion.  I doubt that molluscs can benefit much
from visual detection of UV-illuminated patterns in their shells because (1)
the eyes of molluscs (except Cephalopods) are quite primitive, and are
probably incapable of focusing on patterns or shapes, either by visible
light or by UV;  (2) UV rays don't penetrate more than a few inches into
water, so anything deeper than that would not have access to UV;  (3) in
life, the shells which bear these patterns are often covered by a
periostracum, which would obscure any pattern, either UV or visible light
sensitive.
Regards,
Paul M.