Micromollusk
Encyclopedia
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Mollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
mollusk which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
mollusks, although in addition, numerous species of land snails and freshwater mollusks also reach adult size at very small dimensions.
These tiny mollusks or their tiny shells are easy to overlook, as many of them are not very noticeable to the naked eye, and thus many people are not aware that they even exist. Nonetheless there are large numbers of families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
and vast numbers of mollusk species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, in particular marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
gastropods or sea snails, which are minute enough to be considered micromollusks.
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. Despite their tiny size, many of the shells have a good deal of elaborate sculpture
Sculpture (mollusc)
The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...
. 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
Beachcombing
Beachcombing and beachcomber are words with multiple, but related, meanings that have evolved over time.A beachcomber is someone who "combs" the beach, and the intertidal zone in general, looking for things of value, interest or utility....
, shell collectors and even more serious conchologists
Conchology
Conchology is the scientific or amateur study of mollusc shells. Conchology is one aspect of malacology, the study of molluscs, however malacology studies molluscs as whole organisms, not just their shells. Conchology pre-dated malacology as a field of study. It includes the study of land and...
.
Micromollusks are not very popular as a subject of study, even among professional malacologists, primarily because these minute species can be very challenging to work with. It can often require great care, patience and persistence to find micromollusks, sort them, store them, and identify them correctly. Working with them usually also requires special techniques and special equipment compared with that needed for most of the larger shelled species. Discriminating the features necessary for successful identification of micromollusks to the species level almost always requires a stereo or dissecting microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
. Identifying, or adequately photographing, the smallest species may sometimes require a scanning electron microscope
Scanning electron microscope
A scanning electron microscope is a type of electron microscope that images a sample by scanning it with a high-energy beam of electrons in a raster scan pattern...
. Access to a first rate scientific research library is also often necessary, since many of the popular shell identification books and field guide
Field guide
A field guide is a book designed to help the reader identify wildlife or other objects of natural occurrence . It is generally designed to be brought into the 'field' or local area where such objects exist to help distinguish between similar objects...
s either omit micromollusks completely, or only include a very few species for any particular area.
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 sand grains. Many other micromollusks are from 2 to 4 mm in maximum size; even for people with small hands, this means that the shells are far too small to be picked up with the fingertips using the normal grasping action.
Techniques used
Micromollusks are most often found by the careful searching of sedimentSediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
samples
Sample (material)
In general, a sample is a limited quantity of something which is intended to be similar to and represent a larger amount of that thing. The things could be countable objects such as individual items available as units for sale, or a material not countable as individual items. Samples of countable...
which have been taken from "promising-looking" areas.
Once sediment samples are clean and dry, they are searched under the microscope. Minute shells are picked out using a very small sable
Sable
The sable is a species of marten which inhabits forest environments, primarily in Russia from the Ural Mountains throughout Siberia, in northern Mongolia and China and on Hokkaidō in Japan. Its range in the wild originally extended through European Russia to Poland and Scandinavia...
-hair paintbrush which has been dampened at the tip. Soft entomological tweezers
Tweezers
Tweezers are tools used for picking up and manipulating objects too small to be easily handled with the human hands. They are probably derived from tongs, pincers, or scissors-like pliers used to grab or hold hot objects since the dawn of recorded history...
are also sometimes used.
Micromollusk shells are usually stored in small glass vial
Vial
A vial is a relatively small glass vessel or bottle, especially used to store medication as liquids, powders or in other forms like capsules. They can also be sample vessels; e.g., for use in autosampler devices in analytical chromatography.The glass can be colourless or coloured, clear or amber...
s or in paper micromounts.
Marine sampling
For dead shells of marine species on sandy beaches, these minute empty shells wash up in the lightest deposits of beachBeach
A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...
drift, in more sheltered areas where the very smallest particles of detritus
Detritus
Detritus is a biological term used to describe dead or waste organic material.Detritus may also refer to:* Detritus , a geological term used to describe the particles of rock produced by weathering...
are left behind by the retreating tide
Tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....
; 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
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
sample
Sample (material)
In general, a sample is a limited quantity of something which is intended to be similar to and represent a larger amount of that thing. The things could be countable objects such as individual items available as units for sale, or a material not countable as individual items. Samples of countable...
taken at that spot may contain many more.
Underwater in a marine context, for example when scuba diving
Scuba diving
Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....
, a sediment sample is often taken from areas such as the surface layer of sand under rocks, or at the edge of a coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
. Live micromollusks are also found by washing seaweed
Seaweed
Seaweed is a loose, colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae...
s or algae in fresh water in a bucket.
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 aquatic plants are often collected by passing a plankton net vigorously through and around water weeds so that minute mollusks end up falling into the glass tube
Test tube
A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top, usually with a rounded U-shaped bottom....
at the end of the net. Small bottom-dwelling micromollusks such as Pisidium
Pisidium
Pisidium is a genus of very small or minute freshwater clams known as pill clams or pea clams, aquatic bivalve molluscs in the family Sphaeriidae.-Subgenera and species:Subgenera and species within the genus Pisidium include:...
species are found by scooping a bottom sample of mud into a fine meshed long-handled net, and then agitating it and moving it through the water repeatedly, until only solid particles remain in the net.
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 larvaLarva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l 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 PunctidaePunctidae
Punctidae, common name the "dot snails", is a family of minute air-breathing land snails, terrestrial pulmonate gastropod mollusks or micromollusks in the informal group Sigmurethra ....
and the majority of species in the freshwater bivalve genus Pisidium
Pisidium
Pisidium is a genus of very small or minute freshwater clams known as pill clams or pea clams, aquatic bivalve molluscs in the family Sphaeriidae.-Subgenera and species:Subgenera and species within the genus Pisidium include:...
.
Numerous families of marine gastropods are composed entirely, or almost entirely, of minute species:
- AclididaeAclididaeAclididae is a family of sea snails, marine gastropod mollusks, in the superfamily Eulimoidea.-Taxonomy:Genera in the family Aclididae include:* Abyssoaclis de Barros et al., 2003* Aclis S.L. Lovén, 1846 - type genus...
- AssimineidaeAssimineidaeAssimineidae is a family of minute snails with an operculum that live in saltwater, freshwater or on the land; they are mostly aquatic gastropod mollusks or micromollusks, in the clade Littorinimorpha.- Ecology :...
- CaecidaeCaecidaeCaecidae is a taxonomic family of very small and minute sea snails or micromolluscs, marine gastropod molluscs in the order Littorinimorpha.- Habitat :...
- CerithiopsidaeCerithiopsidaeCerithiopsidae are a family of very small and minute sea snails, marine gastropod molluscs or micromollusks in the informal group Ptenoglossa. Gastropods in this family are known as cerithiopsids....
- CingulopsidaeCingulopsidaeCingulopsidae is a family of sea snails, marine gastropod molluscs in the clade Littorinimorpha.According to taxonomy of the Gastropoda by Bouchet & Rocroi the family Cingulopsidae has no subfamilies.- Genera and species :...
- ElachisinidaeElachisinidaeElachisinidae is a family of sea snails, marine gastropod molluscs in the superfamily Rissooidea and the clade Littorinimorpha.- Taxonomy :Genera within the family Elachisinidae include:* Genus Elachisina W.H...
- EulimidaeEulimidaeEulimidae is a family of very small parasitic sea snails, marine gastropod mollusks in the superfamily Eulimoidea.These small snails live on or in echinoderms and have a proboscis which they extend into their host's body cavity.-Genera:...
- FalsicingulidaeFalsicingulidaeFalsicingulidae is a family of very small sea snails, marine gastropod molluscs in the clade Littorinimorpha.- References :*...
- Fossariidae
- IravadiidaeIravadiidaeIravadiidae is a family of minute sea snails, marine gastropod molluscs in the superfamily Rissooidea and the clade Littorinimorpha.-Genera :Genera within the family Iravadiidae include:* Acliceratia Ponder, 1984* Ceratia H. & A. Adams, 1852...
- JuliidaeJuliidaeJuliidae, common name the bivalved gastropods, is a family of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an opisthobranch group....
, the bivalved gastropods - LimacinidaeLimacinidaeLimacinidae is a family of small sea snails, pteropods, pelagic marine gastropod mollusks in the clade Thecosomata .-Genera:Genera within the family Limacinidae include:...
- LitiopidaeLitiopidaeLitiopidae, common name litiopids, is a family of small sea snails, marine gastropod molluscs in the clade Sorbeoconcha.According to the taxonomy of the Gastropoda by Bouchet & Rocroi the family Litiopidae has no subfamilies.-Genera:...
- MathildidaeMathildidaeMathildidae is a family of minute sea snails, marine gastropod molluscs in the informal group of the Lower Heterobranchia.-Genera:Genera within the family Mathildidae include:* Gegania Jeffreys, 1884* Mathilda Semper, 1865...
- ObtortionidaeObtortionidaeObtortionidae is a family of sea snails, marine gastropod molluscs in the superfamily Cerithioidea, that is within the clade Cerithimorpha or in clade Sorbeoconcha.The shell of the larva is ornamental.- 2005 taxonomy :...
- OmalogyridaeOmalogyridaeOmalogyridae are a family of minute and microscopic sea snails, marine gastropod molluscs or micromolluscs in the informal group Lower Heterobranchia.-Genera:Genera within the family Omalogyridae include:* Ammonicera Vayssiére, 1893...
, the smallest known gastropods, all species are less than 1 mm in adult size - OrbitestellidaeOrbitestellidaeOrbitestellidae are a family of minute sea snails, marine gastropod molluscs or micromolluscs in the informal group Lower Heterobranchia.-Genera:Genera within the family Orbitestellidae include:* Microdiscula* Orbitestella Iredale, 1917...
- PeraclidaePeraclidaePeraclidae is a family of pelagic sea snails or "sea butterflies", marine gastropod mollusks in the superfamily Cymbulioidea.This family has no subfamilies ....
- PyramidellidaePyramidellidaePyramidellidae, common name the pyram family, or pyramid shells, is a voluminous taxonomic family of mostly small and minute ectoparasitic sea snails, marine heterobranch gastropod molluscs or micromolluscs....
- RetusidaeRetusidaeRetusidae is a family of small sea snails, marine opisthobranch gastropod mollusks. They are headshield slugs, in the clade Cephalaspidea.-Genera:Genera within the family Retusidae include:* Coleophysis* Cylichnina Monterosato, 1884...
- RingiculidaeRingiculidaeRingiculidae are a family of minute deep water sea snails or micromolluscs, marine gastropod mollusks or micromollusks in the informal group Lower Heterobranchia.Ringiculidae is the only family within the superfamily Ringiculoidea....
- RissoellidaeRissoellidaeRissoellidae are a family of minute sea snails, marine gastropod molluscs in the informal group Lower Heterobranchia.Rissoellidae is the only family within the superfamily Rissoelloidea in the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005....
- RissoidaeRissoidaeRissoidae is a large family of very small and minute sea snails with an operculum, marine gastropod mollusks in the clade Littorinimorpha.-Distribution and habitat:...
- ScaliolidaeScaliolidaeScaliolidae, common name scaliolids, is a family of sea snails, marine gastropod molluscs in the clade Sorbeoconcha.The sand agglutinates to the teleoconch in Scaliola.- 2005 taxonomy :...
- ScissurellidaeScissurellidaeScissurellidae, sometimes known by the common name little slit snails, are a taxonomic family of minute sea snails, marine gastropod molluscs or micromolluscs in the clade Vetigastropoda...
- Skeneidae
- SkeneopsidaeSkeneopsidaeSkeneopsidae is a family of very small sea snails, marine gastropod molluscs in the clade Littorinimorpha.According to taxonomy of the Gastropoda by Bouchet & Rocroi the family Purpurinidae has no subfamilies.- Genera :* Genus Skeneopsis T...
- TornidaeTornidaeTornidae is a family of very small and minute sea snails with an operculum, marine gastropod mollusks in the clade Littorinimorpha. This family used to be known as the Vitrinellidae.-General characteristics:...
- TriphoridaeTriphoridaeTriphoridae are a family of very small sea snails, marine gastropod molluscs in the informal group Ptenoglossa in the clade Hypsogastropoda. Almost all the species in this family are micromollusks.-Shell description:...
- TruncatellidaeTruncatellidaeTruncatellidae, common name the "looping snails", is a family of small amphibious snails, with gills and an operculum, semi-marine gastropod mollusks or micromollusks.-Shell description :...
- VanikoridaeVanikoridaeVanikoridae is a family of very small or medium sized sea snails, marine gastropod molluscs in the clade Littorinimorpha.- Genera and species :Genera and species within the family Vanikoridae include:* Genus Caledoniella...
Also see:
- ActeonidaeActeonidaeActeonidae, common name the "barrel bubble snails", is a family of small sea snails, marine gastropod mollusks of the informal group Lower Heterobranchia.-Shell description:The shell is usually smaller than 25 mm...
- ActeonoideaActeonoideaActeonoidea is a superfamily of sea snails, or bubble snails, marine gastropod mollusks.- Taxonomy :In the taxonomy of Bouchet & Rocroi , the superfamily Acteonoidea has been included into the informal group "Lower Heterobranchia" , also known as the Allogastropoda.Only one of analyses by Jörger...
- Barleeia and others in the Barleeiidae
Fresh water and land species:
- HydrobiidaeHydrobiidaeHydrobiidae, common name mud snails, is a large cosmopolitan taxonomic family of very small freshwater snails and brackish water snails that have an operculum, aquatic gastropod mollusks in the clade Littorinimorpha.- Distribution :...
(a freshwater family) - Truncatella
- PisidiumPisidiumPisidium is a genus of very small or minute freshwater clams known as pill clams or pea clams, aquatic bivalve molluscs in the family Sphaeriidae.-Subgenera and species:Subgenera and species within the genus Pisidium include:...
in the family SphaeriidaeSphaeriidaeThe Sphaeriidae are a family of small to minute freshwater bivalve molluscs, in the order Veneroida. In the USA they are commonly known as the pea clams and the fingernail clams.-Genera:Genera in the family Sphaeriidae include:* Musculium...
, freshwater bivalves
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