freshwater mollusc
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Freshwater molluscs are those members of the
Phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. The plural of a noun typically denotes a q ...
Mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the grammatical number, grammatical category of number. ...

Mollusca
which live in
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water Water is an Inorganic compound, inorganic, Transparency and translucency, transparent, tasteless, odorless, and Color of water, nearly colorless chemical subs ...
habitat Ibex in an alpine habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat c ...

habitat
s, both
lotic River ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energ ...
(flowing water) such as rivers, streams, canals, springs, and cave streams (
stygobite Stygofauna are any fauna that live in groundwater systems or aquifers, such as caves, fissures and vugs. Stygofauna and troglofauna are the two types of subterranean fauna (based on life-history). Both are associated with subterranean environments ...
species) and
lentic A lake ecosystem or lacustrine ecosystem includes biotic component, biotic (living) plants, animals and micro-organisms, as well as abiotic component, abiotic (non-living) physical and chemical interactions. Lake ecosystems are a prime example of ...
(still water) such as lakes, ponds (including temporary or
vernal pond Vernal pools, also called vernal ponds or ephemeral pools, are seasonal pools of water that provide habitat for distinctive plants and animals. They are considered to be a distinctive type of wetland usually devoid of fish, and thus allow the safe ...
s), and ditches. This article is about freshwater Mollusca in general; for information on one particular family of freshwater molluscs, please follow the appropriate links in the lists below. The two major classes of molluscs have representatives in freshwater: the
gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may a ...
s (snails) and the
bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of marine and freshwater Mollusca, molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged p ...
(freshwater
mussel Mussel () is the used for members of several families of s, from saltwater and habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other edible clams, which are often more or less rounded or ...

mussel
s and
clam Clam is a common name for several kinds of bivalve mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000  extant species In ...

clam
s.) It appears that the other classes within the Phylum Mollusca -the
cephalopods A cephalopod is any member of the mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant taxon, extant species of molluscs are ...
,
scaphopod The tusk shells or tooth shells, technically the Scaphopoda (the scaphopods , from Ancient Greek σκᾰ́φης ''skáphē'' "boat" and πούς ''poús'' "foot"), are members of a of shelled with worldwide distribution, and are the only ...
s, polyplacophorans, etc. - never made the transition from a fully marine environment to a freshwater environment. A few species of freshwater molluscs are among the most notorious
invasive species Kudzu, a Japanese vine species invasive in the southeast United States, growing in Atlanta, Georgia (U.S. state), Georgia An invasive species is an introduced species, introduced organism that becomes overpopulated and negatively alters its n ...
. In contrast, numerous others have become threatened or have become extinct in the face of
anthropogenic Anthropogenic ("human" + "generating") is an adjective that may refer to: * Anthropogeny, the study of the origins of humanity Counterintuitively, anthropogenic may also refer to things that have been generated by humans, as follows: * Human imp ...
change.


Biogeography

Typical freshwater species (such as many river mussel species in the family
Unionidae The Unionidae are a Family (biology), family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is at ...
) have a range (biology), range which may consist of a series of adjacent river systems, a series of adjacent tributaries, or part of a single large river system. Large rivers and small tributary creeks typically share few species, and distribution patterns suggest large lowland rivers represent substantial barriers to the dispersal of species adapted to small upland streams. Endemism is common in some families, and species may be endemic to a single creek or spring. In contrast, some of the tiny Pisidium, pill clams have a nearly worldwide distribution (Burch, 1972)


Ecological and anatomical challenges

Challenges in the natural environment faced by freshwater Mollusca include floods, droughts, siltation, extreme temperature variations, predation, and the constant unidirectional flow characteristic of river habitats. Osmoregulation, or the maintenance of constant salinity within body tissue and fluids, is another challenge faced by freshwater Mollusca. Dillon (2000)Dillon, Robert T. 2000. The Ecology of Freshwater Molluscs. Cambridge University Press. 509 pp. indicates that they have characteristically low tissue salinities relative to other freshwater animals, and unionid mussels have some of the lowest tissue salinities of any animal.


Freshwater bivalves

Families of freshwater bivalves occur within the orders Unionida and Venerida.


Freshwater gastropods

Ten families of prosobranchiate snails (gilled operculum (gastropod), operculate snails) and five pulmonate families (lunged snails, distantly related to common landsnails) inhabit freshwater environments in many parts of the world. Some freshwater snail species serve as host (biology), hosts for human and animal parasites.


See also

*List of non-marine molluscs of the United States


References

{{reflist


External links


Freshwater Mollusk Conservation Society


Freshwater molluscs,