![Columella edentula](https://upload.wikimedia.org/wikipedia/commons/f/f9/Columella_edentula.jpg)
A micromollusk is a
shelled mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to
marine 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
shell
Shell may refer to:
Architecture and design
* Shell (structure), a thin structure
** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses
** Thin-shell structure
Science Biology
* Seashell, a hard o ...
s 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 (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideal ...
and vast numbers of mollusk
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
, in particular
marine gastropods
The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, from freshwater, and from land. The ...
or sea
snails
A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...
, 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 is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable sc ...
. 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
malacologist
Malacology is the branch of invertebrate zoology that deals with the study of the Mollusca (mollusks or molluscs), the second-largest phylum of animals in terms of described species after the arthropods. Mollusks include snails and slugs, clams, ...
s, 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
A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisibl ...
. Identifying, or adequately photographing, the smallest species may sometimes require a
scanning electron microscope. Access to a first rate scientific research library is also often necessary, since many of the popular shell identification books and
field guide
A field guide is a book designed to help the reader identify wildlife (flora or fauna) or other objects of natural occurrence (e.g. rocks and minerals). It is generally designed to be brought into the "field" or local area where such objects exi ...
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 grain
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...
s. 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 fingers using the normal grasping action.
Techniques used
Micromollusks are most often found by the careful searching of
sediment
Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
samples 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-hair paintbrush which has been dampened at the tip. Soft
entomological
Entomology () is the scientific study of insects, a branch of zoology. In the past the term "insect" was less specific, and historically the definition of entomology would also include the study of animals in other arthropod groups, such as arach ...
tweezers
Tweezers are small hand tools used for grasping objects too small to be easily handled with the human fingers. Tweezers are thumb-driven forceps most likely derived from tongs used to grab or hold hot objects since the dawn of recorded history. ...
are also sometimes used. Shells this small are usually stored in small glass
vial
A vial (also known as a phial or flacon) is a small glass or plastic vessel or bottle, often used to store medication as liquids, powders or capsules. They can also be used as scientific sample vessels; for instance, in autosampler devices i ...
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
beach
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shel ...
drift, in more sheltered areas where the very smallest particles of
detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
are left behind by the retreating
tide
Tides are the rise and fall of sea levels caused by the combined effects of the gravity, gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another.
Tide t ...
; 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 is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand an ...
sample
Sample or samples may refer to:
Base meaning
* Sample (statistics), a subset of a population – complete data set
* Sample (signal), a digital discrete sample of a continuous analog signal
* Sample (material), a specimen or small quantity of s ...
taken at that spot may contain many more.
Underwater in a marine context, for example when
scuba diving
Scuba diving is a mode of underwater diving whereby divers use breathing equipment that is completely independent of a surface air supply. The name "scuba", an acronym for "Self-Contained Underwater Breathing Apparatus", was coined by Chris ...
, 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
A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups.
C ...
. Live micromollusks are also found by washing
seaweed
Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
s or
alga
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...
e 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
Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes to distinguish them from algae and other microphytes. A macrophyte is a plant that ...
are often collected by passing a
plankton net
A plankton net is equipment used for collecting samples of plankton in standing bodies of water. It consists of a towing line and bridles, nylon mesh net, and a cod end. Plankton nets are considered one of the oldest, simplest and least expensi ...
vigorously through and around water weeds so that minute mollusks end up falling into the
glass tube
Glass tubes are mainly cylindrical hollow-wares. Their special shape combined with the huge variety of glass types (like borosilicate, flint, aluminosilicate, soda lime, lead or quartz glass), allows the use of glass tubing in many applications. Fo ...
at the end of the net. Small bottom-dwelling micromollusks such as ''
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, the pea clams and fingernail clams.
In some bivalve classification systems, the family S ...
'' 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
larva
A larva (; plural larvae ) 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.
The ...
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
![BMNSM micromollusks](https://upload.wikimedia.org/wikipedia/commons/9/9f/BMNSM_micromollusks.jpg)
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
Punctidae, common name the "dot snails" or "pinhead snails", is a family of minute air-breathing land snails, terrestrial pulmonate gastropod mollusks or micromollusks in the informal group Sigmurethra (according to the taxonomy of the Ga ...
and the majority of species in the freshwater bivalve genus ''
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, the pea clams and fingernail clams.
In some bivalve classification systems, the family S ...
''.
Numerous families of marine gastropods are composed entirely, or almost entirely, of minute species:
*
Aclididae
*
Assimineidae
*
Caecidae
Caecidae is a taxonomic family of very small and minute sea snails or micromolluscs, marine gastropod molluscs in the order Littorinimorpha.Bouchet, P.; Gofas, S. (2013). Caecidae. Accessed through: World Register of Marine Species at http ...
*
Cerithiopsidae
*
Cingulopsidae
Cingulopsidae is a family of sea snails, marine gastropod molluscs in the clade Littorinimorpha
Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails (marine species), but also including some freshwater sna ...
*
Elachisinidae
Elachisinidae is a family of sea snails, marine gastropod molluscs in the superfamily Truncatelloidea and the order Littorinimorpha
Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails (marine species) ...
*
Eulimidae
Eulimidae is a family of very small parasitic sea snails, marine gastropod mollusks in the superfamily Vanikoroidea.
Description
These small parasitic snails live on (or in some cases in) the bodies of echinoderms such as sea cucumbers ...
*
Falsicingulidae
Falsicingulidae is a family of very small sea snails, marine gastropod molluscs in the clade Littorinimorpha
Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails (marine species), but also including s ...
*
Fossariidae
Planaxidae, commonly called planaxids or clusterwinks, are a taxonomic family of small and minute sea snails, pantropical marine gastropod molluscs in the superfamily Cerithoidea. They live on rocky shores in the littoral zone of the tropics an ...
*
Iravadiidae
Iravadiidae is a family of minute sea snails, marine gastropod molluscs in the superfamily Truncatelloidea and the clade Littorinimorpha
Littorinimorpha is a large order of snails, gastropods, consisting primarily of sea snails (marine sp ...
*
Juliidae
Juliidae, common name the bivalved gastropods, is a family of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an opisthobranch group. MolluscaBase eds. (2021). MolluscaBase. Juliidae E. A. Smith ...
, the bivalved gastropods
*
Limacinidae
The Limacinidae are a family of small sea snails, pteropods, pelagic marine gastropod mollusks in the clade Thecosomata ( sea butterflies).Bouchet, P. (2012). Limacinidae. Accessed through: World Register of Marine Species at http://www.marinesp ...
*
Litiopidae
Litiopidae, 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 (2005) the family Litiopidae has no subfamilies.
Gen ...
*
Mathildidae
Mathildidae is a family of minute sea snails, marine gastropod molluscs in the superfamily Mathildoidea of the informal group of the Lower Heterobranchia.Bouchet, P.; Gofas, S. (2012). Mathildidae. Accessed through: World Register of Marin ...
*
Obtortionidae
Obtortionidae 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
According to the ...
*
Omalogyridae, the smallest known gastropods, all species are less than 1 mm in adult size
*
Orbitestellidae
*
Peraclidae
Peraclidae is a family of pelagic sea snails or "sea butterflies", marine gastropod mollusks in the superfamily Cymbulioidea.
This family has no subfamilies (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).
This fami ...
*
Pyramidellidae
Pyramidellidae, 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. The great majority of species of pyrams are micromol ...
*
Retusidae
Retusidae is a family of very small sea snails, barrel-bubble snails, marine opisthobranch gastropod mollusks. These are headshield slugs, in the superfamily Bulloidea
Bulloidea is a superfamily of sea snails, or bubble snails, marine gastro ...
*
Ringiculidae
Ringiculidae are a family of minute deep water sea snails, marine gastropod mollusks or micromollusks in the informal group Lower Heterobranchia.Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. ''Cla ...
*
Rissoellidae
Rissoellidae are a family (biology), family of minute sea snails, marine (ocean), marine gastropod molluscs in the informal group Lower Heterobranchia.
Rissoellidae is the only family within the superfamily Rissoelloidea in the Taxonomy of the G ...
*
Rissoidae
Rissoidae is a large family of very small and minute sea snails with an operculum, marine gastropod mollusks in the superfamily Rissooidea and the order Littorinimorpha
Littorinimorpha is a large order of snails, gastropods, consisting pr ...
*
Scaliolidae
Scaliolidae, common name scaliolids,Strong E. E., Colgan D. J., Healy J. M., Lydeard C., Ponder W. F. & Glaubrecht M. (2011). "Phylogeny of the gastropod superfamily Cerithioidea using morphology and molecules". ''Zoological Journal of the Linne ...
*
Scissurellidae
Scissurellidae, 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 (according to the taxonomy of the Gastropoda by Bouchet & ...
*
Skeneidae
*
Skeneopsidae
*
Tornidae
Tornidae is a family (biology), family of very small and minute sea snails with an Operculum (gastropod), operculum, marine (ocean), marine gastropod mollusks in the clade Littorinimorpha. This family used to be known as the Vitrinellidae.Bouchet ...
*
Triphoridae
*
Truncatellidae
Truncatellidae, 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
This family of snails have small shells which lose th ...
*
Vanikoridae
Vanikoridae is a family of minute to medium-sized sea snails, marine gastropod molluscs in the superfamily Vanikoroidea.
Genera and species
Genera within the family Vanikoridae include:
* '' Amamiconcha'' Habe, 1961
* '' Berthais'' Melv ...
Also see:
*
Acteonidae
*
Acteonoidea
Acteonoidea is a superfamily of sea snails, or bubble snails, marine gastropod mollusks.
Taxonomy
In the taxonomy of Bouchet & Rocroi (2005), the superfamily Acteonoidea has been included into the informal group "Lower Heterobranchia" ( ...
* ''
Barleeia'' and others in the
Barleeiidae
Fresh water and land species:
*
Hydrobiidae
Hydrobiidae, commonly known as mud snails, is a large cosmopolitan family of very small freshwater and brackish water snails with an operculum; they are in the order Littorinimorpha.
Distribution
Hydrobiidae are found in much of the world, ...
(a freshwater family)
*
''Truncatella''
* ''
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, the pea clams and fingernail clams.
In some bivalve classification systems, the family S ...
'' in the family
Sphaeriidae
Sphaeriidae is a family of small to minute freshwater bivalve molluscs in the order Sphaeriida. In the US, they are commonly known as pea clams or fingernail clams. Heard, William H. 1977. Reproduction of fingernail clams (Sphaeriidae: ''Sphae ...
, freshwater bivalves
References
{{Reflist
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 a
Conchologists of America
Mollusc anatomy
Microscopic animals