Through a Looking Glass: Micromollusks
by Ross Gunderson -
University of Wisconsin - Parkside
There is a largely unseen group
of shells on the world's beaches. They are the micromollusks,
shells which have all the beauty of their larger counterparts,
but which remain unseen due to their small size. There are no
definite guidelines about when a shell is considered a micromollusk,
but a workable range is from about 3/16" down to about
1/32". They abound on the same beaches on which you find
larger shells, but you have to look very closely to find them.
Better yet, look through a magnifying glass! A whole new world
of shell collecting now opens up, one with miniature revolving
glassy spires, exquisite crenelated towers, subtle curves, alluring
proportions, and symmetry. This world can be truly appreciated
only by using a simple magnifying glass or a microscope. The
sense of discovery is exhilarating and is enhanced by the fact
that most shellers walk right by these shells, not knowing the
veritable treasure around and under their feet. Now when I walk
on a beach and hear the rasp of the sand and the crunch of shells
under foot, I wonder what miniature shell marvel I may have
What is a Micromollusk?
A micromollusk is more than just a small shell. The 3/16"
down to 1/32" range applies to adult shells. A very young
Busycon contrarium (Conrad, 1840) fits in this size range, but
is not considered a micromollusk because its adult size ranges
from 4" to 16". There are additional differences.
For example, the adult shells of micros are mainly very sturdy
in comparison to young shells of larger species. Also the protoconch
may be about the size of an entire micromollusk shell, while
the protoconch of a micro is correspondingly small. Of course,
please remember that there are always exceptions.
Where does one find micromollusks? The answer to this question
is rather indirect: look for places where wave action and beach
topography will concentrate them, rather than looking directly
for them. Find slowly sloping beaches with moderate to low wave
action. Since the micromollusks are relatively light they have
a tendency to follow the water line down the beach as the tide
recedes. With very little wave action they are left behind as
the tide goes out.This area defined by high and low tide lines
is called the littoral zone. In either case you will see a coarse
grit, composed of small 1/8" and smaller flat pieces as
well as rounded pieces, which is hopefully rich in micromollusks.
Before taking a sample, look at it with a small magnifying glass.
If you see some micros collect a larger sample.
Another place where nature concentrates micromollusks is in
depressions in the bottom below low tide line and at the base
of heads of corals and coral reefs. This area is called the
sublittoral zone. Look in depressions for the coarse grit mentioned
above. You can pursue this activity in shallow water with a
water glass (e.g. a coffee can with a clear plastic bottom)
or with a mask and snorkel in deeper water. At this point I
must digress. My wife and I were collecting in the Florida Keys
using a water glass, and there was a small child watching us.
He proudly got an old fashioned white enameled dipper from his
mom, and proceeded to follow us around holding the dipper to
the water and peering into it. He was having so much fun that
I didn't have the heart to tell him our coffee can had a plastic
bottom we could see through.
You can also collect micromollusks
on rock shores with higher wave action. Remember that the micromollusks
are relatively light, so wave action will pick them up and deposit
them farther in shore in rocky depressions. This is the situation
in which I collect a lot of my Caribbean micros. The Caribbean
islands have, as their shoreline, many miles of coral reefs,
eroded, fossilized and pockmarked with small and large depressions
which collect sediment brought in by the waves.
Collecting and Sample Preparation:
Both large and small kitchen strainers are ideal for obtaining
samples from the water. Small garden or masonry trowels are
ideal for collecting samples from the beach or rocky depressions.
Place your samples in plastic bags with an indelible location
label. Sort your samples by removing larger and smaller unwanted
debris (e.g. sand and larger shell fragments). This sorting
is easily accomplished by using sieves, purchased from scientific
supply houses or built from square wood frames (and 12"
to 18" square) onto which window screen (1/32" diameter
holes) or 1/8" hardware cloth has been attached. Stack
your hardware cloth sieve on top of one with window screen.
Place your sample on the top sieve and run fresh water through
the sample while gently shaking the sieves side to side. Don't
worry, micros are relatively tough little shells. The window
screen will allow fine sand to pass through while retaining
micros and other debris. The larger holed sieve will retain
larger unwanted fragments. Keep what didn't go through the window
screen, and bake it in an oven at its lowest setting until dry.
Sorting Your Samples:
A small, folding 10X hand lens is a must. If you can afford
it, a dissecting microscope is preferable and easier to use
(Edmund Scientific). In addition, small tweezers and paint brushes
(#1 or smaller) are required for picking up your micros. You'll
need a black background, such as black cardboard or a piece
of stiff plastic painted black. Use a good light source such
as a small halogen reading lamp which can be directed on your
sample. Now is your chance to discover the previously unseen
world of micros. Spread a small amount of material on the black
background. Using your hand lens or microscope slowly scan the
sample. You will quickly find out that most of your sample is
not made up of micros, but rather larger silica sand particles,
bits of sea urchin spines and tests, coral fragments, and shell
fragments. Eureka! I've found a micro! How do I pick it up?
Depending upon its size and sturdiness there are two methods
of approach. The tweezers can be used for larger sturdy micros,
but beware, the micros may react much like a watermelon or pumpkin
seed pressed between ones fingers! Zip, and it is gone in an
unpredictable direction. How far did it go and in what direction?
You can always get on your hands and knees and look for it or
sweep/vacuum the floor and look through the trash. On a bad
day they may go zipping along for a distance of three or four
feet. An even more distressing end result is to crush the micro
into dust between the tips of the tweezers. The preferred method
is to use a wet paint brush. Dip the brush in clean water and
touch it to a tissue to remove excess water. Touch it to your
micro and presto, it's stuck. I delicately scrape the micro
off into a small glass jar.
I temporarily store my micros, along with a data label, in small
watchmaker's cases (Lee Valley Tools) while they are being identified.
After identification, the smallest shells are placed in a smaller
glass or plastic vial with an identification number and sealed
in using a cotton stopper. The vial and shell are then placed
back into the watchmaker's case and the identification number
is written on the data label. The larger micros (e.g. Anachis
obesa (C. B. Adams, 1845), simply remain in the watchmake's
case. Long term storage of micros follows the same precautions
as for larger shells:
Store in darkness
Paper or materials in contact with the shell should be acid
Keep the humidity as low as possible
Most of these requirements can be provided by putting the watchmaker's
cases into smaller plastic boxes and placing them into larger
airtight food storage containers which are then placed in a
dark cabinet. My first micros have been with me for forty years
and still look great.
Identification of Micromollusks:
How do you identify micros? The same as with any other shell:
plenty of hard work. My experience has taught me to take several
pictures of each micro in different positions and lighting.
You can leisurely view the pictures without the distraction
of squinting through a lens. I use the pictures during the initial
phases of identification.
The most common micros are found in the popular guides. However,
many of the more uncommon micromollusks are either not found
in the popular shell identification books or are spread throughout
a great number of books which may or may not be readily available.
My first approach is to sit down with all of my books and look
at the pictures. This hopefully will produce a tentative identification
to either the genus or species level. I then cross check to
see if the physical characteristics of the shell match those
found in more than one book. During this phase I re-examine
the shell with magnification to observe fine details. The next
step is to show it to all of your fellow shell collectors and
ask for their opinions. Does this identify the shell? Not necessarily.
There are usually many more species in each genus than you realize
[e.g. American Conchologist 1996 24(4):16-17]. The next step
is to consult an expert on the particular genus of your shell;
experts are usually able to give you the appropriate specific
name. As a last resort, compare the shell with other museum
material and finally the taxonomic type for the species. If
it matches the characteristics of the type, your identification
is complete. Of course the real answer to the question depends
on what level of certainty of identification you are comfortable
Department of Biological
Science, Wisconsin University, Parkside, Box 2000, Kenosha,
WI 53141 Email: email@example.com Ross Gunderson is the one
of the two recipients of the first annual Walter Sage Memorial
Grant. His article on microshells also appears in the March
1997 issue of American Conchologist.
Vokes, H. E. and E. H. Vokes, 1983. Distribution
of shallow water marine mollusca, Yucatan Penninsula, Mexico.
Publication 54 Mesoamerica Ecology Institute Monographs, Middle
American Research Institute, Tulane University, Louisiana.
DeJong, K. M. and H. E. Coomans, 1988. Marine gastropods from
Curacao, Aruba and Bonaire. E. J. Brill, U.S.A.
Warmke, G. L. and R. T. Abbott, R. T. Caribbean seashells .
Dover Publications, New York.