The Unionidae are a

family 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. Idea ...

of freshwater mussels, the largest in the order Unionida, the

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, biv ...

molluscs sometimes known as river mussels, or simply as unionids. The range of distribution for this family is world-wide. It is at its most diverse in North America, with about 297 recognised taxa, but China and Southeast Asia also support very diverse faunas. Freshwater mussels occupy a wide range of habitats, but most often occupy lotic waters, i.e. flowing water such as rivers, streams and creeks.

Origin and early diversification

The recent phylogenetic study reveals that the Unionidae most likely originated in Southeast and East Asia in the Jurassic, with the earliest expansions into North America and Africa (since the mid-Cretaceous) followed by the colonization of Europe and India (since the Paleocene).

Life history

Unionidae burrow into the substrate, with their posterior margins exposed. They pump water through the incurrent aperture, obtaining

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as we ...

and food. They remove phytoplankton and zooplankton, as well as suspended bacteria, fungal spores, and dissolved organic matter.Silverman, H., Nichols S.J, Cherry J.S., Archberger E., Lynn J.S., Dietz T.H. (1997). "Clearance of laboratory-cultured bacteria by freshwater bivalves: differences between lentic and lotic unionids." Canadian Journal of Zoology 75: 1857-1866. Despite extensive laboratory studies, which of these filtrates unionoids actually process remains uncertain. In high densities, they have the ability to influence water clarity but filtration rates are dependent on water temperature, current velocity, and particle size and concentration. In addition, gill morphology can determine particle size filtered, as well as the rate.

Reproduction

Unionidae are distinguished by a unique and complex lifecycle. Most unionids are of separate sex, although some species, such as '' Elliptio complanata'', are known to be hermaphroditic. The sperm is ejected from the

mantle A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...

cavity through the male's excurrent aperture and taken into the female's mantle cavity through the incurrent aperture. Fertilised eggs move from the gonads to the gills ( marsupia) where they further ripen and metamorph into glochidia, the first larval stage. Mature glochidia are released by the female and then attach to the

gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...

s, fins, or skin of a host

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% ...

. A cyst is quickly formed around the glochidia, and they stay on the fish for several weeks or months before they fall off as

juvenile Juvenile may refer to: *Juvenile status, or minor (law), prior to adulthood *Juvenile (organism) *Juvenile (rapper) (born 1975), American rapper * ''Juvenile'' (2000 film), Japanese film * ''Juvenile'' (2017 film) *Juvenile (greyhounds), a greyho ...

mussels, which then bury themselves in the sediment. Some of the species in the Unionidae, commonly known as pocketbook mussels, have evolved a remarkable reproductive strategy. The edge of the female's body that protrudes from the valves of the shell develops into an imitation of a small fish complete with markings and false eyes. This decoy moves in the current and attracts the attention of real fish. Some fish see the decoy as prey, while others see a conspecific, i.e. a member of their own species. Whatever they see, they approach for a closer look and the mussel releases huge numbers of larvae from her gills, dousing the inquisitive fish with her tiny, parasitic young. These glochidial larvae are drawn into the fish's gills, where they attach and trigger a tissue response that forms a small cyst in which the young mussel resides. It feeds by breaking down and digesting the tissue of the fish within the cyst. Sex is determined by a region located on the mitochondrial DNA, the male open-reading frame (M-ORF) and female open-reading frame (F-ORF). Hermaphroditic mussels lack these regions and contain a female-like open-reading frame dubbed hermaphroditic open-reading frame (H-ORF). In many mussels, the hermaphroditic state is ancestral and the male sex evolved later. This region of the mitochondria also may be responsible for the evolution of doubly uniparental inheritance seen in freshwater mussels.

Taxonomy

Genera by taxonomic order

The following classification is based on MolluscaBase and the MUSSEL Project database: * Subfamily Ambleminae ** Tribe Lampsilini *** Genus '' Epioblasma'' *** Genus '' Lampsilis'' *** Genus '' Potamilus'' *** Genus '' Actinonaias'' *** Genus '' Cambarunio'' *** Genus '' Obovaria'' *** Genus '' Toxolasma'' *** Genus ''

Medionidus ''Medionidus'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or s ...

'' *** Genus '' Ptychobranchus'' *** Genus '' Disconaias'' *** Genus '' Leaunio'' *** Genus ''

Venustaconcha ''Venustaconcha'' is a genus of freshwater mussels, Aquatic animal, aquatic bivalve mollusks in the family Unionidae. Species Species within the genus ''Venustaconcha'' include: * ''Venustaconcha ellipsiformis'' * ''Venustaconcha pleasii'' Ref ...

'' *** Genus '' Cyrtonaias'' *** Genus '' Hamiota'' *** Genus ''

Sagittunio ''Sagittunio'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae. Species There are four recognized species: * '' Sagittunio aldermani'' Watters, 2018 * ''Sagittunio nasutus'' (Say, 1817) * ''Sagittunio subros ...

'' *** Genus ''

Truncilla ''Truncilla'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or si ...

'' *** Genus '' Villosa'' *** Genus '' Arotonaias'' *** Genus '' Cyprogenia'' *** Genus '' Delphinonaias'' *** Genus '' Ortmanniana'' *** Genus '' Pachynaias'' *** Genus '' Atlanticoncha'' *** Genus '' Dromus'' *** Genus '' Ellipsaria'' *** Genus '' Friersonia'' *** Genus '' Glebula'' *** Genus '' Lemiox'' *** Genus '' Ligumia'' *** Genus '' Obliquaria'' *** Genus '' Paetulunio'' ** Tribe Pleurobemini *** Genus '' Elliptio'' *** Genus '' Pleurobema'' *** Genus ''

Fusconaia ''Fusconaia'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae. They are native to North America. Species within the genus ''Fusconaia'' Species include: * ''Fusconaia askewi'' * ''Fusconaia burkei'' (Tape ...

'' *** Genus ''

Plethobasus ''Plethobasus'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or ...

'' *** Genus '' Pleuronaia'' *** Genus ''

Parvaspina ''Parvaspina'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae. It contains only two critically endangered species, both endemic to river basins in a small region of the southeastern United States The S ...

'' *** Genus '' Elliptoideus'' *** Genus '' Eurynia'' *** Genus ''

Hemistena The cracking pearlymussel (''Hemistena lata'') is an endangered species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae. This species is native to the United States, where it remains only in Tennessee and Virginia. ...

'' ** Tribe Popenaiadini *** Genus '' Nephronaias'' *** Genus '' Psoronaias'' *** Genus '' Barynaias'' *** Genus '' Popenaias'' *** Genus '' Sphenonaias'' *** Genus '' Micronaias'' *** Genus '' Nephritica'' *** Genus '' Reticulatus'' *** Genus '' Martensnaias'' ** Tribe

Quadrulini Ambleminae is a subfamily of freshwater mussel in the family Unionidae. They are found throughout much of eastern North America south to Central America, although fossils are also known from Siberia. Some species have also been introduced to East ...

*** Genus ''

Cyclonaias The Unionidae are a 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 its most diver ...

'' *** Genus '' Theliderma'' *** Genus '' Uniomerus'' *** Genus '' Quadrula'' *** Genus ''

Megalonaias ''Megalonaias'' is a genus of bivalves belonging to the family Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. The ran ...

'' *** Genus '' Tritogonia'' ** Tribe

Amblemini Ambleminae is a subfamily of freshwater mussel in the family Unionidae. They are found throughout much of eastern North America south to Central America, although fossils are also known from Siberia. Some species have also been introduced to Eas ...

*** Genus ''

Amblema ''Amblema'' is a genus of freshwater mussels, aquatic bivalve 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 e ...

'' *** Genus '' Regianaia'' *** Genus '' Plectomerus'' * Subfamily

Unioninae Unioninae is a subfamily of freshwater mussels in the family Unionidae. This superfamily has a wide distribution, being found throughout Eurasia, North America (including Central America) and Africa. Systematics The following classification i ...

** Tribe Anodontini *** Subtribe Alasmidontina **** Genus '' Alasmidonta'' **** Genus '' Lasmigona'' **** Genus ''

Pyganodon ''Pyganodon'' is a genus of freshwater mussels, aquatic bivalve mollusks in the subfamily Unioninae of the family Unionidae, the river mussels.MolluscaBase eds. (2022). MolluscaBase. Pyganodon Crosse & P. Fischer, 1894. Accessed through: World ...

'' **** Genus '' Utterbackiana'' **** Genus ''

Strophitus ''Strophitus'' is a genus of freshwater mussels, aquatic bivalve mollusks in the family Unionidae, the river mussels. Species within the genus ''Strophitus'' * ''Strophitus connasaugaensis'' * ''Strophitus subvexus'' * ''Strophitus undula ...

'' **** Genus '' Utterbackia'' **** Genus ''

Anodontoides ''Anodontoides'' is a genus of freshwater mussels, an aquatic bivalve mollusk in the family Unionidae, the river mussels.Rosenberg, G.; Bouchet, P. (2012). Anodontoides. Accessed through: World Register of Marine Species at http://www.marinesp ...

'' **** Genus ''

Arcidens ''Arcidens'' is a genus of freshwater mussels, aquatic bivalve molluscs in the family Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or sim ...

'' **** Genus '' Pseudodontoideus'' **** Genus ''

Pegias ''Pegias'' is a monotypic genusUSFWS''Pegias fabula'' Recovery Plan.September 1989. of freshwater mussels in the family Unionidae. This genus contains the single species ''Pegias fabula'', known commonly as the littlewing pearlymussel. Distri ...

'' **** Genus ''

Simpsonaias ''Simpsonaias ambigua'', the salamander mussel or mudpuppy mussel, is a species of bivalve in the family Unionidae. It is unique among freshwater mussels in using mudpuppies as its glochidial host. It is the only freshwater mussel known to have a ...

'' *** Subtribe Cristariina **** Genus '' Sinanodonta'' **** Genus '' Buldowskia'' **** Genus '' Cristaria'' **** Genus '' Anemina'' **** Genus '' Beringiana'' **** Genus '' Pletholophus'' **** Genus '' Simpsonella'' **** Genus '' Amuranodonta'' *** Subtribe Anodontina **** Genus ''

Anodonta ''Anodonta'' is a genus of freshwater mussels in the family Unionidae, the river mussels. Species Species in this genus include: * ''Anodonta anatina'' Linné, 1758 – duck mussel * '' Anodonta beringiana'' Middendorff, 1851 – Yukon f ...

'' **** Genus '' Pseudanodonta'' ** Tribe Unionini *** Genus ''

Unio Unio may refer to: * ''Unio'' (bivalve), a genus of freshwater mussels * ''Unio'' (sternwheeler), a steamboat that operated in Oregon, United States, in 1861, before being renamed ''Union'' * UNI/O, an asynchronous serial bus * UNIO Satu Mare, a ...

'' *** Genus ''

Nodularia ''Nodularia'' is a genus of filamentous nitrogen-fixing cyanobacteria, or blue-green algae. They occur mainly in brackish or salinic waters, such as the hypersaline Makgadikgadi Pans, the Peel-Harvey Estuary in Western Australia or the Baltic Sea ...

'' *** Genus '' Aculamprotula'' *** Genus '' Acuticosta'' *** Genus '' Cuneopsis'' *** Genus '' Inversiunio'' *** Genus '' Pseudobaphia'' *** Genus '' Rhombuniopsis'' *** Genus '' Lepidodesma'' *** Genus '' Pseudocuneopsis'' *** Genus '' Schistodesmus'' *** Genus '' Arcuneopsis'' *** Genus '' Diaurora'' *** Genus '' Middendorffinaia'' *** Genus '' Protunio'' ** Tribe Lanceolariini *** Genus '' Lanceolaria'' * Subfamily Gonideinae ** Tribe Pseudodontini *** Subtribe Pilsbryoconchina **** Genus '' Sundadontina'' **** Genus '' Monodontina'' **** Genus '' Pilsbryoconcha'' **** Genus '' Bineurus'' **** Genus '' Thaiconcha'' **** Genus '' Namkongnaia'' **** Genus '' Nyeinchanconcha'' *** Subtribe Pseudodontina **** Genus ''

Pseudodon ''Pseudodon'' is a genus of bivalvia of the Unionidae family that is native to East and Southeast Asia. There are 14 recognized species. Description The taxon was described by John Gould from his findings at the Salween River Basin in British ...

'' ** Tribe Contradentini *** Genus ''

Lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements'' ...

'' *** Genus '' Yaukthwa'' *** Genus '' Physunio'' *** Genus '' Trapezoideus'' *** Genus '' Pressidens'' *** Genus '' Solenaia'' ** Tribe Lamprotulini *** Genus '' Lamprotula'' *** Genus ''

Potomida ''Potomida'' is a genus of bivalves belonging to the subfamily Gonideinae of the family Unionidae. MolluscaBase eds. (2022). MolluscaBase. Potomida. Accessed through: World Register of Marine Species at: http://www.marinespecies.org/aphia.php?p= ...

'' *** Genus '' Schepmania'' *** Genus '' Discomya'' *** Genus '' Pronodularia'' ** Tribe Rectidentini *** Genus '' Hyriopsis'' *** Genus '' Ensidens'' *** Genus '' Ctenodesma'' *** Genus '' Elongaria'' *** Genus '' Khairuloconcha'' *** Genus '' Prohyriopsis'' *** Genus '' Rectidens'' ** Tribe Gonideni *** Genus '' Ptychorhynchus'' *** Genus '' Sinosolenaia'' *** Genus '' Inversidens'' *** Genus '' Leguminaia'' *** Genus '' Parvasolenaia'' *** Genus '' Gonidea'' *** Genus '' Koreosolenaia'' *** Genus ''

Microcondylaea ''Microcondylaea'' is a genus of freshwater mussels in the family Unionidae The Unionidae are a family of freshwater mussels, the largest in the order Unionida, the bivalve molluscs sometimes known as river mussels, or simply as unionids. ...

'' *** Genus '' Obovalis'' *** Genus '' Pseudodontopsis'' ** Tribe Chamberlainini *** Genus '' Sinohyriopsis'' *** Genus '' Chamberlainia'' *** Genus '' Caudiculatus'' * Subfamily Parreysiinae ** Tribe Coelaturini *** Genus '' Coelatura'' *** Genus '' Nitia'' *** Genus '' Nyassunio'' *** Genus '' Prisodontopsis'' *** Genus '' Brazzaea'' *** Genus '' Grandidieria'' *** Genus '' Moncetia'' *** Genus ''

Pseudospatha ''Pseudospatha tanganyicensis'' a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels. It is the only species in the genus ''Pseudospatha''. This species is endemic to Lake Tanganyika where found ...

'' ** Tribe Indochinellini *** Genus '' Indonaia'' *** Genus '' Scabies'' *** Genus '' Radiatula'' *** Genus '' Harmandia'' *** Genus '' Indochinella'' *** Genus '' Scabiellus'' *** Genus '' Unionetta'' ** Tribe Lamellidentini *** Genus '' Lamellidens'' *** Genus '' Trapezidens'' *** Genus '' Arcidopsis'' ** Tribe Leoparreysiini *** Genus '' Leoparreysia'' ** Tribe Parreysiini *** Genus '' Parreysia'' *** Genus '' Balwantia'' * Genus '' Haasodonta'' (subfamily ''incertae sedis'') * Genus '' Germainaia'' (subfamily ''incertae sedis'') * Subfamily Modellnaiinae ** Genus '' Modellnaia''

Genera by alphabetic order and region

Widespread * ''

'' * ''

'' Africa * '' Brazzaea'' * '' Coelatura'' * '' Germainaia'' * '' Grandidieria'' * '' Mweruella'' * '' Nitia'' * '' Nyassunio'' * '' Prisodontopsis'' * ''

'' Central America and Mexico * '' Arotonaias'' * '' Barynaias'' * '' Cyrtonaias'' * '' Delphinonaias'' * '' Disconaias'' * '' Friersonia'' * '' Martensnaias'' * '' Micronaias'' * '' Nephritica'' * '' Nephronaias'' * '' Pachynaias'' * '' Popenaias'' * '' Psoronaias'' * '' Psorula'' * '' Reticulatus'' * '' Sphenonaias'' Eastern Asia * '' Aculamprotula'' * '' Acuticosta'' * '' Anemina'' * '' Arconaia'' * '' Bineurus''C. T. Simpson, 1900 * '' Caudiculatus'' * '' Chamberlainia'' * '' Contradens'' * '' Cristaria'' * '' Ctenodesma'' * '' Cuneopsis'' * '' Discomya'' * '' Elongaria'' * '' Ensidens'' * '' Harmandia'' * '' Hyriopsis'' * '' Inversidens'' * '' Inversiunio'' * '' Lamprotula'' * '' Lanceolaria'' * '' Lepidodesma'' * '' Modellnaia'' * '' Monodontina'' Conrad, 1853 * ''

'' * '' Oxynaia'' * '' Physunio'' * '' Pilsbryoconcha'' * '' Pressidens'' * '' Prohyriopsis'' * '' Pronodularia'' * '' Protunio'' * '' Pseudobaphia'' * ''

'' * '' Ptychorhynchus'' * '' Rectidens'' * '' Rhombuniopsis'' * '' Scabies'' * '' Schepmania'' * '' Schistodesmus'' * '' Simpsonella'' * '' Sinanodonta'' * '' Solenaia'' * '' Sundadontina'' Bolotov et al., 2020 * '' Thaiconcha'' Bolotov et al., 2020 * '' Unionetta'' Europe * ''

'' * '' Pseudanodonta'' India * '' Arcidopsis'' * '' Lamellidens'' * '' Parreysia'' * '' Radiatula'' * '' Trapezoideus'' * '' Yaukthwa'' Middle East * '' Leguminaia'' * '' Pseudodontopsis'' New Guinea * '' Haasodonta'' North America * '' Actinonaias'' * '' Alasmidonta'' * ''

'' * ''

'' * '' Cyprogenia'' * '' Dromus'' * '' Ellipsaria'' * '' Elliptio'' * '' Elliptoideus'' * '' Epioblasma'' * ''

'' * '' Glebula'' * '' Gonidea'' * '' Hamiota'' * ''

'' * '' Lampsilis'' * '' Lasmigona'' * '' Lemiox'' * '' Leptodea'' * '' Ligumia'' * ''

'' * ''

'' * '' Obliquaria'' * '' Obovaria'' * ''

'' * '' Plectomerus'' * ''

'' * '' Pleurobema'' * '' Pleuronaia'' * '' Potamilus'' * '' Psoronaias'' Crosse & P. Fischer, 1894 * '' Ptychobranchus'' * ''

'' * '' Quadrula'' * ''

Reginaia ''Reginaia '' is a genus of freshwater mussels, aquatic bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies ...

'' * '' Rotundaria'' * ''

'' * ''

'' * '' Theliderma'' * '' Toxolasma'' * ''

'' * '' Uniomerus'' * '' Utterbackia'' * ''

'' * '' Villosa''

Fossilization and taphonomic implications

In large enough quantities, unionid shells can have enough of an impact on environmental conditions to affect the ability of organic remains in the local environment to fossilize. For example, in the Dinosaur Park Formation, fossil hadrosaur eggshell is rare because the breakdown of tannins from local coniferous vegetation would have caused the ancient waters to become acidic. Eggshell fragments are present in only two microfossil sites, both of which are dominated by the preserved shells of invertebrate life, including unionids. The slow dissolution of these shells releasing calcium carbonate into the water raised the water's pH high enough to prevent the eggshell fragments from dissolving before they could be fossilized.Tanke, D.H. and Brett-Surman, M.K. 2001. Evidence of Hatchling and Nestling-Size Hadrosaurs (Reptilia:Ornithischia) from Dinosaur Provincial Park (Dinosaur Park Formation: Campanian), Alberta, Canada. pp. 206-218. In: Mesozoic Vertebrate Life—New Research Inspired by the Paleontology of Philip J. Currie. Edited by D.H. Tanke and K. Carpenter. Indiana University Press: Bloomington. xviii + 577 pp.

References

External links

Missouri State Unio Gallery

Freshwater Mollusk Conservation Society

* ttps://web.archive.org/web/20090304195016/http://bama.ua.edu/~musselp/proj/grano_salis/unionidae.html Unionidae at The MUSSEL Project Web Site {{Taxonbar, from=Q1434366 Bivalve families Extant Middle Jurassic first appearances