When I go to other Islands in the Pacific on collecting/photo trips I
usually find about 90 to 120 different species of the area to
photograph.  The mix of species is always different except for about 20
most common species.  I invariably find on return home that some of the
species I identified turned out to be different from first guess, and
add to the new "shallow reef" species photographed.  On very close
examination a very few shells that are identical to a "common" species
are actually a different species as indicated by different animals,
opercula or protoconchs.  [Different overall color of a protoconch does
not always make for a new species, but different shape/sculpture usually
will]

In the home area where I kept returning to the same places, new species
kept turning up after 30 years.  Specimens are brought into an area by
storms (deep water shells washed into tide pools or shallow water
shells washing down cliffs), or the velligers being brought into an area
from outside areas or adjacent areas.  There always be some additions to
old lists given enough time.  What you see depends on how and when you
collect.  My dive buddy of 40 years would always come up with a
different list from mine of what was seen on a single dive although we
were in sight of each other througout most dives.  Luck and different
recognition patterns play a big part in what you see.

--
                     Aloha from Wesley M. Thorsson
Editor of Internet Hawaiian Shell News, a monthly Internet Publication
           122 Waialeale St, Honolulu, HI  96825-2020,  U.S.A
       http://www.hits.net/~hsn                 [log in to unmask]