Micromollusk
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A micromollusk is a
These tiny mollusks or their tiny
Considerable numbers of marine gastropod species are only about 5 or 6 mm in adult size; many others are only about 2 or 3 mm in adult size; and a few have adult shells which are as small as one millimeter or even smaller still. Micromollusks are known to have adult shells as small as 600 µm.[1] [2] Despite their tiny size, many of the shells have a good deal of elaborate sculpture. A fair number of them are even quite colorful, although many others are colorless and translucent.
Certain species of micromollusks are very common in the right habitat, and can on occasion be present in huge numbers. However, because of their minute size, micromollusks often go unnoticed by beachcombers, shell collectors and even more serious conchologists.
Micromollusks are not very popular as a subject of study, even among professional
Because of all these various challenges, micromollusks are poorly known compared to their larger relatives, and thus there are undoubtedly numerous species which have yet to be discovered and described.
Defining the size
There is currently no universally acceptable definition for the upper limit of the size range for micromollusks. Because of this, the exact use of the word varies from one expert to another; however, the maximum size of the shell of a micromollusk species is usually 5 mm to 7 mm, around one quarter of an inch or less.
The shells of the very smallest micromollusks are less than one millimeter in adult size, and thus they are truly microscopic, smaller in fact than some
Techniques used
Micromollusks are most often found by the careful searching of
Marine sampling
For dead shells of marine species on sandy beaches, these minute empty shells wash up in the lightest deposits of beach drift, in more sheltered areas where the very smallest particles of detritus are left behind by the retreating tide; this is often in a rather flat and level part of the beach. When at least some minute shells are seen on close visual inspection, a sediment sample taken at that spot may contain many more.
Underwater in a marine context, for example when
Non-marine sampling
Land micromollusks are often found by taking samples of leaf litter from rich areas, subsequently sieving or sifting the litter, and then searching it under a strong light and magnification.
Freshwater micromollusks which live on
Because most empty land snail shells and many empty freshwater shells float, another effective way to sample dead shells from an area can be to sort through river drift, the accumulations of small floating bits and pieces left behind by creeks and rivers after floods.
Excluded from the category
Juveniles or larval stages of larger species of mollusk are not considered to be micromollusks, even though these immature shells may sometimes be very small indeed, and may often be encountered in the same sediment samples where micromollusks are found.
Examples
The word "micromollusk" is used most often for marine shelled species, although a reasonable number of land and freshwater species are also small enough to qualify as micromollusks: for example, the land snail family Punctidae and the majority of species in the freshwater bivalve genus Pisidium.
Numerous families of marine gastropods are composed entirely, or almost entirely, of minute species:
- Aclididae
- Assimineidae
- Caecidae
- Cerithiopsidae
- Cingulopsidae
- Elachisinidae
- Eulimidae
- Falsicingulidae
- Fossariidae
- Iravadiidae
- Juliidae, the bivalved gastropods
- Limacinidae
- Litiopidae
- Mathildidae
- Obtortionidae
- Omalogyridae, the smallest known gastropods, all species are less than 1 mm in adult size
- Orbitestellidae
- Peraclidae
- Pyramidellidae
- Retusidae
- Ringiculidae
- Rissoellidae
- Rissoidae
- Scaliolidae
- Scissurellidae
- Skeneidae
- Skeneopsidae
- Tornidae
- Triphoridae
- Truncatellidae
- Vanikoridae
Also see:
- Acteonidae
- Acteonoidea
- Barleeia and others in the Barleeiidae
Fresh water and land species:
- Hydrobiidae (a freshwater family)
- Truncatella
- Pisidium in the family Sphaeriidae, freshwater bivalves
References
Further reading
- Geiger D. L., Marshall B. A., Ponder W. F., Sasaki T. & Warén A. (2007). "Techniques for collecting, handling, preparing, storing and examining small molluscan specimens". Molluscan Research 27(1): 1-50. abstract.
- Rosenberg G. (1992). The encyclopedia of seashells, Dorset Press, New York
External links
- An article about micromollusks at Conchologists of America