Unionidae

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 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 and food. They remove phytoplankton and zooplankton, as well as suspended bacteria, fungal spores, and dissolved organic matter. 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 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 gills, fins, or skin of a host fish. 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 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
Genus Ptychobranchus
Genus Disconaias
Genus Leaunio
Genus Venustaconcha
Genus Cyrtonaias
Genus Hamiota
Genus Sagittunio
Genus Truncilla
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
Genus Plethobasus
Genus Pleuronaia
Genus Parvaspina
Genus Elliptoideus
Genus Eurynia
Genus Hemistena
Tribe Popenaiadini
Genus Nephronaias
Genus Psoronaias
Genus Barynaias
Genus Popenaias
Genus Sphenonaias
Genus Micronaias
Genus Nephritica
Genus Reticulatus
Genus Martensnaias
Tribe Quadrulini
Genus Cyclonaias
Genus Theliderma
Genus Uniomerus
Genus Quadrula
Genus Megalonaias
Genus Tritogonia
Tribe Amblemini
Genus Amblema
Genus Reginaia
Genus Plectomerus
Subfamily Unioninae
Tribe Anodontini
Subtribe Alasmidontina
Genus Alasmidonta
Genus Lasmigona
Genus Pyganodon
Genus Utterbackiana
Genus Strophitus
Genus Utterbackia
Genus Anodontoides
Genus Arcidens
Genus Pseudodontoideus
Genus Pegias
Genus Simpsonaias
Subtribe Cristariina
Genus Sinanodonta
Genus Buldowskia
Genus Cristaria
Genus Anemina
Genus Beringiana
Genus Pletholophus
Genus Simpsonella
Genus Amuranodonta
Subtribe Anodontina
Genus Anodonta
Genus Pseudanodonta
Tribe Unionini
Genus Unio
Genus Nodularia
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
Tribe Contradentini
Genus Lens
Genus Yaukthwa
Genus Physunio
Genus Trapezoideus
Genus Pressidens
Genus Solenaia
Tribe Lamprotulini
Genus Lamprotula
Genus Potomida
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
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
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
Anodonta
Potomida
Unio
Africa
Brazzaea
Coelatura
Germainaia
Grandidieria
Mweruella
Nitia
Nyassunio
Prisodontopsis
Pseudospatha
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
BineurusC. T. Simpson, 1900
Caudiculatus
Chamberlainia
Contradens
Cristaria
Ctenodesma
Cuneopsis
Discomya
Elongaria
Ensidens
Harmandia
Hyriopsis
Inversidens
Inversiunio
Lamprotula
Lanceolaria
Lepidodesma
Modellnaia
Monodontina Conrad, 1853
Nodularia
Oxynaia
Physunio
Pilsbryoconcha
Pressidens
Prohyriopsis
Pronodularia
Protunio
Pseudobaphia
Pseudodon
Ptychorhynchus
Rectidens
Rhombuniopsis
Scabies
Schepmania
Schistodesmus
Simpsonella
Sinanodonta
Solenaia
Sundadontina Bolotov et al., 2020
Thaiconcha Bolotov et al., 2020
Unionetta
Europe
Microcondylaea
Pseudanodonta
India
Arcidopsis
Lamellidens
Parreysia
Radiatula
Trapezoideus
Yaukthwa
Middle East
Leguminaia
Pseudodontopsis
New Guinea
Haasodonta
North America
Actinonaias
Alasmidonta
Amblema
Anodontoides
Arcidens
Cyprogenia
Dromus
Ellipsaria
Elliptio
Elliptoideus
Epioblasma
Fusconaia
Glebula
Gonidea
Hamiota
Hemistena
Lampsilis
Lasmigona
Lemiox
Leptodea
Ligumia
Medionidus
Megalonaias
Obliquaria
Obovaria
Pegias
Plectomerus
Plethobasus
Pleurobema
Pleuronaia
Potamilus
Psoronaias Crosse & P. Fischer, 1894
Ptychobranchus
Pyganodon
Quadrula
Reginaia
Rotundaria
Simpsonaias
Strophitus
Theliderma
Toxolasma
Truncilla
Uniomerus
Utterbackia
Venustaconcha
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.
References
External links
Missouri State Unio Gallery
Freshwater Mollusk Conservation Society
Ohio State University: Division of Molluscs - Freshwater Mussel Collection - Unionidae
Unionidae at The MUSSEL Project Web Site
Bivalve families
Extant Middle Jurassic first appearances