Methodology
This is a new resource page that provides information on the collecting, processing and storing of non-marine mollusks. Feel free to contact me with additional and innovative collection or separation techniques. I will be happy to post them here.
The collection of aquatic and terrestrial mollusks is simple and typically doesn't require any specialized equipment. The processing is a little different and depends on whether you are doing picking in the field or in the laboratory.
Aquatics
Sampling
Collect with strainer - An ordinary stainless steel kitchen strainer can be dragged through vegetation or against channel bank or bottom. If used to collect bank or bottom sample, be sure to scrape into the sediments to ensure the collection of bivalves and bottom dwelling gastropods. Samples should mostly fill a quart-sized freezer bag. Be sure to label the bag with date, collector, and specific location (ex. 7/5/04 - transit 2, west side of channel - Dyer).
Collect with bottom sampler - If a bottom sampler is available sample from the edges and center of the channel. Samples can be placed directly in a white pan for picking or placed in a quart-sized or larger freezer bag for later screening and picking.
Sieving
Screens should be No. 32 or 35 (~500 μm) to catch small bivalves and gastropods. This size is sufficient for collecting ostracodes as well. Be sure not to roughly agitate sediments as the smaller mollusks and ostracodes are extremely fragile. Try to break up sediment clumps with water pressure only. If that is not sufficient try an ultrasonic or soap bath. Soaking in Calgon dish washing liquid or OxyClean will often soften a sediment clump sufficiently to break it up easily. Once sieved, place the remaining material on a drying rack, preferably with a screen-wire bottom, covered with paper towels and dry over night.
Terrestrials
Sampling
Terrestrial mollusks are found in virtually every environment on earth. While they are hardy, they do require a source of moisture. That suggests the best place to find them is in rock crevices, in leaf litter, under logs and downfalls and under overhangs. In arid environments, springs, seeps, cienegas, at the edge of rock outcrops, etc. are common habitats for mollusks. Look at the base of grass clumps. If you see debris accumulations, grab some. Again collect as much as a quart-sized freezer bag will hold. If collecting in leaf litter or under downfalls, be sure to collect some soil. I try to collect about an inch of soil or humus along with the surface material; leaves, trigs and debris.
Sieving
Use No. 32 or 35 screens (~500 μm) and wash the sediments. Again be careful to use minimal pressure when breaking up clumps. The same methods listed for aquatic sieving may be used here. Dry in the same fashion as aquatic mollusks.
Picking
There is no completely satisfactory automated method to separating mollusks from sediments. As technologically oriented as I am, I am not sure I would want to devise such a system as the process of looking through a microscope or magni-visor has a calming effect on my grey matter and allows my mind to wonder and think about how these mollusks came to be where they were found and how they might be transported elsewhere. Some interesting hypotheses have come during the mollusk picking process. Enough prose, now on to the method. In the field, it is best to place the sediments in a white pan. Most mollusks are darker colored and stand out nicely against the white background. In the lab, and if mollusks are large enough to see clearly with the unaided eye, simply pick the mollusks from the sediments on the drying rack. I find this method is fine for getting an idea of what species are present but often the smaller or less clearly distinct mollusks are not seen. Mollusks may also be attached to debris and difficult to see unless viewed under magnification. A better way is to take about a teaspoon of sediments and place them in a Petri dish half. Shake the dish to distribute the sediments evenly then pick the mollusks under a 10x or 20x stereomicroscope. Use whatever method works best for you but I find that searching the sediments by moving the Petri dish left and right while moving the sediments toward the bottom of the Petri dish with a dental tool ensures that I don’t miss any of the small or immature mollusks. Remove the mollusks with a pair of very light weight forceps. BioQuip sells a very functional pair of featherweight forceps but the best I have found come from Wiha Tools. They are thin stainless steel foil and come at a rather pricey $27 but if you need to handle extremely fragile mollusks, they are worth the money. Consider a specimen that is a one-of-a-kind and you crush it in the process of picking...AAAHHHH!!! I suggest using forceps even for the larger mollusks, unless you are talking about something the size of an Apple snail, because the oils from your fingers can cause any number of problems. If these are modern mollusks, they may become discolored and loose surface features. If they are fossil mollusks and they are destined to be used for dating purposes, the chemicals from your fingers will skew the actual age of the specimen. Always use forceps. It just makes more sense.
Storage
The nice thing about mollusks is they don’t require any special storage requirements. The only caution is to keep large and small specimens separated. Most terrestrial mollusks are very small, some as small as 2 mm. These are best stored in a gelatin capsule inside a stoppered vial. Larger specimens can be stored in box lined with cotton. Be sure to label specimens with locality, date, genus and species, if possible, and the name of the collector. The vials can be stored in a vial storage box. So little is known about mollusks of the western United States that a reference collection from any locality can be of great value.
Last modified January 2005
by Dave Dyer
Return to my home page