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 obliterated.
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 free 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 with.
Department of Biological Science, Wisconsin University, Parkside, Box 2000, Kenosha, WI 53141 Email: firstname.lastname@example.org 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.