Yes, many species of cowries are transversely banded when juvenile, but not
all.  Some are unicolored, with no markings at all, while others have very
pretty, dense reticulated patterns, almost tented in some cases.  I believe
the Cypraea arabica complex and Cypraea mauritiana, and some others have such
patterns.  In those species which are banded as juveniles, the juvenile
pattern is usually somewhat visible under the adult pattern, even when they
are fully mature.
Another person e-mailed me privately and asked for some information on cowrie
reproduction.  I was going to respond privately, but since I'm here and
cowries is the topic, I'll just add what little I know about it to this post:
Cowries have separate sexes, that is, a given animal is either a male or a
female (lest that sound pitifully obvious, let me hasten to add that this is
NOT the situation for all invertebrates).  Fertilization is internal.  The
female keeps the fertilzed eggs in her brood pouch for several weeks, then
lays them in tough capsules, often under rocks or coral debris, or in a
sheltered hole in the reef.  One female can produce several hundred capsules,
each of which can contain several hundred eggs.  Such overproduction is
common among marine invertebrates, and even fish (vertebrates), because the
dangers are so numerous, and the mortality rate so high.  The female cowrie
often sits on the eggs for several weeks, until they hatch.  This obviously
is not "incubation", as in birds, but she does keep the egg capsules clean
and probably protects them somewhat from would-be predators. The eggs hatch
into free-swimming ciliated larvae called veligers, which as Lynn mentioned,
have a microscopic shell with cancellate sculpture.  The veligers continue to
add to the shell as they grow, forming a conical shell of several whorls,
which eventually becomes too heavy to remain suspended in the water.  This
can take anywhere from several days to several weeks, depending on the
species and other factors.  At that point they sink to the bottom, and begin
to grow into the "bulla form", which looks rather like an elongate bubble
shell, or a thin, lightweight olive shell.  The beginning bulla is only a few
millimeters in length, but the bulla grows to nearly the full adult size of
the animal.  Then the thin lip of the bulla curls under, and apertural teeth
form, giving the shell the slot-like aperture of an adult cowrie.  After
that, there is little additional increase in shell length, though the shell
does get thicker and heavier.
Paul M.