If all individuals are too much alike, an abundant species is vulnerable to
predators and parasites. It is usual for common species like these strombids
to have high diversity, in genes and/or outward form.

To elaborate, a predator that searches for snails by sight may be confused
by snails that have a great diversity of size, shape, and color pattern.
Likewise, for predators that search by the sense of smell, it may be
confusing if some of the prey specializes on eating apples and some on
oranges. Some of the prey will smell "wrong". And bacteria and viruses
spread more easily through species whose individuals are all alike; the
microbes do not have to adapt to different kinds of hosts in that case.

High diversity in a species is often a sign of an effective defense against
long-term predation. Of course, it can also be a sign of no predation at
all, allowing all the mutant offspring to live! But that probably isn't as
common a situation.

Andrew K. Rindsberg
Geological Survey of Alabama