Epioblasma brevidens - (I. Lea, 1831)
Cumberlandian Combshell
Synonym(s): Plagiola brevidens (I. Lea, 1831)
Taxonomic Status: Accepted
Related ITIS Name(s): Epioblasma brevidens (I. Lea, 1831) (TSN 80304)
Unique Identifier: ELEMENT_GLOBAL.2.115217
Element Code: IMBIV16030
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
Image 11989

Public Domain

 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Epioblasma
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Concept Reference
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Concept Reference: Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.
Concept Reference Code: B98TUR01EHUS
Name Used in Concept Reference: Epioblasma brevidens
Taxonomic Comments: This species has been synonymized mistakenly under Obliquaria (Plagiola) interrupta Rafinesque, 1820, by Johnson (1978). Rafinesque's description of the latter species in actuality is a varient of Ptychobranchus fasciolaris (Rafinesque, 1820); however, Johnson and Baker (1973) designated a female Epioblasma brevidens as the lectotype for O. interrupta. This action removed E. brevidens to the junior synonymy of O. interrupta and relegated Epioblasma as a junior synonym of Plabiola. This error is in the process of being corrected with a proposal to the ICZN to suppress Johnson and Baker's lectotype designation. E. brevidens is being used in anticipation of acceptance of this proposal.
Conservation Status
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NatureServe Status

Global Status: G1
Global Status Last Reviewed: 28Apr2009
Global Status Last Changed: 28Oct2003
Rounded Global Status: G1 - Critically Imperiled
Reasons: Populations are restricted to limited areas of five river drainages (less than 2000 sq. km occupied habitat) and some of these may no longer be reproducing. The area of occupancy has declined significantly (> 80% decline) and all populations are in decline due to pollution, particularly from mining activities, and the inundation of habitat by reservoirs.
Nation: United States
National Status: N1 (15Dec1998)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Alabama (S1), Kentucky (S1), Mississippi (S1), Tennessee (S1), Virginia (S1)

Other Statuses

U.S. Endangered Species Act (USESA): LE, XN: Listed endangered, nonessential experimental population (10Jan1997)
Comments on USESA: Listed Endangered throughout its range, except in the free-flowing reach of the Tennessee River from the base of Wilson Dam downstream to the backwaters of Pickwick Reservoir and the lower 5 RM of all tributaries to this reach in Colbert and Lauderdale Counties, Alabama. Here it is listed as an experimental, non-essential population. (Federal Register, 14 June 2001).

The USFWS, in cooperation with the State of Tennessee and Conservation Fisheries, Inc., announced a final rule to reintroduce this species into its historical habitat in the free-flowing reach of the French Broad River below Douglas Dam to its confluence with the Holston River, Knox County Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (Federal Register, 12 September 2007). The proposed rule for this action was published on June 13, 2006.

U.S. Fish & Wildlife Service Lead Region: R4 - Southeast
IUCN Red List Category: CR - Critically endangered
American Fisheries Society Status: Endangered (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 250-1000 square km (about 100-400 square miles)
Range Extent Comments: Historically, this species was distributed throughout the Cumberlandian region of the Tennessee and Cumberland river systems in Alabama, Kentucky, Mississippi, Tennessee, and Virginia (USFWS, 2003; 2004). Populations are currently known from Buck Creek in Kentucky; through a few miles of the Big South Fork Cumberland River in Kentucky and Tennessee; and in very low numbers in the Powell and Clinch rivers in Virginia and Tennessee (USFWS, 1997). A few, likely non-reproducing populations associated with sub-lotic sections of some reservoirs (e.g., Old Hickory Reservoir on the Cumberland River). In 1997 several fresh dead specimens were found by Jeff Garner in Bear Creek, a tributary of the Tennessee River in northwestern Alabama and according to Tom Mann (Mississippi Natural Heritage Program) fresh dead shells were found in Mississippi in September 2000 (see also McGregor and Garner, 2004). Currently, it is restricted to five stream reaches (USFWS, 2003; 2004). In Mississippi, it is found only in the Tennessee River drainage in extreme northeastern portion of state (Jones et al., 2005). In Alabama, the only known extant population is in a short (6 km) reach of Bear Creek, in the vicinity of Natchez Trace Parkway, Colbert Co. (Williams et al., 2008).

Area of Occupancy: 501-12,500 4-km2 grid cells
Area of Occupancy Comments: Recently, critical habitat was designated for the Duck River (0 river km occupied, 74 river km unoccupied habitat) in Tennessee, Bear Creek (40 river km occupied, 0 river km unoccupied habitat) in Alabama and Mississippi, Powell River (154 river km occupied, 0 river km unoccupied habitat) in Tennessee and Virginia, Clinch River (242 river km occupied, 0 river km unoccupied habitat) in Tennessee and Virginia, Nolichucky River (0 river km occupied, 8 river km unoccupied habitat) in Tennessee, Big South Fork (43 river km occupied, 0 river km unoccupied habitat) in Tennessee and Kentucky, and Buck Creek (58 river km occupied, 0 river km unoccupied habitat) in Kentucky (USFWS, 2004).

Number of Occurrences: 1 - 5
Number of Occurrences Comments: Current populations occur in Buck Creek (Pulaski County, Kentucky), Big South Fork Cumberland River (Scott County, Tennessee and McCreary County, Kentucky) (USFWS, 2003; 2004). In the Tennessee River system, populations are thought to remain in the Powell River (Lee County, Virginia and Claiborne and Hancock Counties, Tennessee), Clinch River (Scott County, Virginia and Hancock County, Tennessee), North Fork Holston River (Scott County, Virginia- reintroduced), and Bear Creek (Colbert County, Alabama and Tishimingo County, Mississippi) (USFWS, 2003; 2004). Currently restricted to five stream reaches (USFWS, 2003; 2004). Hubbs (2002) reported relictual shells only in the Elk River at Dickey Bridge (RM 105.4) (see also Isom et al., 1973). In Mississippi, found only in Tennessee River drainage in extreme northeastern portion of state (Jones et al., 2005). In Alabama, the only known extant population is in a short (6 km) reach of Bear Creek, in the vicinity of Natchez Trace Parkway, Colbert Co. (Williams et al., 2008).

Population Size: 50 - 2500 individuals
Population Size Comments: Densities have been calculated by Ahlstedt and Tuberville (1997) at 0.97, 0.54, 0.32, and 0.11 per square foot in the Powell River (over 14-16 sites) in 1979, 1983, 1988, and 1994, respectively, and 0.32, 0.65, and 0.76 per square foot in the Clinch River (11-14 sites) in 1979, 1988 and 1994, respectively.

Number of Occurrences with Good Viability/Integrity: Very few (1-3)
Viability/Integrity Comments: Barr et al. (1994) determined (based on 1981 survey data) that viable populations exist in the Clinch and Powell Rivers. Viable populations include the Clinch River (Virginia and Tennessee) with smaller populations in the Buck Creek, Big South Fork Cumberland, Powell River, Duck River (USFWS, 2003; 2004). The Bear Creek population is potentially an important source of genetic diversity since it is more than 700 river km removed from the Clinch River population (Williams et al., 2008).

Overall Threat Impact: Very high - high
Overall Threat Impact Comments: Much of the information below is derived from and expanded upon in USFWS (2004):
The greatest threat to this species in the Cumberlandian Region is habitat alteration. Principal causes include impoundments, channelization, pollution, and sedimentation that have altered or eliminated those habitats that are essential to the long-term viability of many riverine mussel populations. Impoundments result in the elimination of riffle and shoal habitats, disruption of a river's ecological processes, elimination of current and the covering of rocky and sand substrates by fine sediments, and alteration of downstream water quality and riverine habitat. Daily discharge fluctuations, bank sloughing, seasonal oxygen deficiencies, cold-water releases, turbulence, high silt loads, and altered host fish distribution have contributed to limited mussel recruitment and skewed demographics. Impoundments, as barriers to dispersal, contribute to the loss of local populations by blocking postextirpation recolonization. Population losses due to impoundments have probably contributed more to the decline of the Cumberlandian combshell, oyster mussel, and rough rabbitsfoot and most other Cumberlandian Region mussels than any other single factor (as the Cumberland elktoe and purple bean generally inhabit smaller rivers, impoundments have had less of an impact on them, although the impact is still significant).

The entire length of the Tennessee River and much of the Cumberland River is maintained as a navigation channel with a series of locks and dams--nine on the Tennessee River and four on the Cumberland River. Channel maintenance activities continue to cause substrate instability and alteration in these rivers and may serve to diminish what habitat remains for the recovery of riverine species.

Heavy metal-rich drainage from coal mining and associated sedimentation have adversely impacted many stream reaches, destroying mussel beds and preventing natural recolonization. Acid mine runoff may be having local impacts on the recruitment of, particularly, the Cumberland elktoe, since most of its range is within watersheds where coal mining is still occurring. Impacts associated with coal mining activities have particularly altered upper Cumberland River system streams with diverse historical mussel faunas and have been implicated in the decline of Epioblasma species, especially in the Big South Fork. Strip mining continues to threaten mussels in coal field drainages of the Cumberland Plateau with increased sedimentation loads and acid mine drainage, including Cumberland elktoe and Cumberlandian combshell populations. The Marsh Creek population of the Cumberland elktoe has also been adversely affected and is still threatened by potential spills from oil exploration activities. Coal mining activities also occur in portions of the upper Powell and Clinch River systems, primarily in Virginia. Polycyclic aromatic compounds (PAHs) are indicative of coal fines in the bottom sediments of streams. Known to be toxic to mussels and fishes, PAHs have been found at relatively high levels in the upper portions of the Clinch and Powell Rivers in Virginia.

In-stream gravel mining has been implicated in the destruction of mussel populations. Negative impacts include riparian forest clearing (e.g., mine site establishment, access roads, lowered floodplain water table); stream channel modifications (e.g., geomorphic instability, altered habitat, disrupted flow patterns [including lowered elevation of stream flow], sediment transport); water quality modifications (e.g., increased turbidity, reduced light penetration, increased temperature); macroinvertebrate population changes (e.g., elimination, habitat disruption, increased sedimentation); and changes in fish populations (e.g., impacts to spawning and nursery habitat, food web disruptions). Gravel mining activities threaten the Cumberlandian combshell populations in the Powell River and in Buck Creek, the latter stream representing one of only two remaining populations of this species in the entire Cumberland River system. Mining activities on the Elk River may have played a role in the extirpation of the oyster mussel and Cumberlandian combshell from that river.

Contaminants contained in point and nonpoint discharges can degrade water and substrate quality and adversely impact, if not destroy, mussel populations. Although chemical spills and other point sources (e.g., ditch, swale, artificial channel, drainage pipe) of contaminants may directly result in mussel mortality, widespread decreases in density and diversity may result, in part, from the subtle, pervasive effects of chronic low-level contamination. Mussels appear to be among the most intolerant organisms to heavy metals, several of which are lethal, even at relatively low levels. Among other pollutants, ammonia has been shown to be lethal to mussels. Common contaminants associated with households and urban areas, particularly those from industrial and municipal effluents, may include heavy metals, ammonia, chlorine, phosphorus, and numerous organic compounds. Nonpoint-source runoff from urban areas tends to have the highest levels of many pollutants, such as phosphorus and ammonia, when compared to other catchments. Agricultural sources of chemical contaminants are considerable and include two broad categories--nutrients and pesticides. Nutrient enrichment generally occurs as a result of runoff from livestock farms and feedlots and from fertilizers used on row crops. Pesticide runoff that commonly ends up in streams may have effects (based on studies with laboratory-tested mussels) that are particularly profound.

Numerous Cumberlandian Region streams have experienced mussel kills from toxic chemical spills and other causes. The high number of jeopardized species in the upper Tennessee River system make accidental spills a particular concern to conservationists and resource managers.

Sedimentation, including siltation runoff, has been implicated as the number one factor in water quality impairment in the United States. Specific biological impacts on mussels from excessive sediment include reduced feeding and respiratory efficiency from clogged gills, disrupted metabolic processes, reduced growth rates, increased substrate instability, limited burrowing activity, and physical smothering. Host fish/mussel interactions may be indirectly impacted by changes in stream sediment regimes through three mechanisms: fish abundance, diversity, and reproduction reduced; impedes host fish attractant mechanisms; interfere with the ability of some species' adhesive conglutinates to adhere to rock particles. Waterborne sediment is produced by the erosion of stream banks, channels, plowed fields, unpaved roads, roadside ditches, upland gullies, and other soil disturbance sites. Agricultural activities produce the most significant amount of sediment that enters streams. Silvicultural sedimentation impacts are more the result of logging roads than the actual harvesting of timber.

Developmental activities associated with urbanization (e.g., highways, building construction, infrastructure creation, recreational facilities) may contribute significant amounts of sediment and other pollutants in quantities that may be detrimental to stream habitats. With development, watersheds become more impervious, resulting in increased storm-water runoff into streams and a doubling in annual flow rates in completely urbanized streams. Impervious surfaces may reduce sediment input into streams but result in channel instability by accelerating storm-water runoff, which increases bank erosion and bed scouring. Water withdrawals for agricultural irrigation and municipal and industrial water supplies are an increasing concern for all aquatic resources and are directly correlated with expanding human populations. This impact has the potential to be a particular problem for the Cumberland elktoe population in the Big South Fork system and the oyster mussel population in the Duck River.

The alien Asian clam (Corbicula flumminea) was first reported from the Cumberlandian Region around 1959. This species has been implicated as a competitor with native mussels for resources such as food, nutrients, and space, particularly as juveniles. Densities of Asian clams are sometimes heavy in Cumberlandian Region streams, making competition with populations of some of these five species likely. Paradoxically, large, seemingly healthy, populations of unionids may coexist with Asian clams. The invasion of the nonnative zebra mussel (Dreissena polymorpha) poses a threat to the mussel fauna of the Cumberlandian Region. Although zebra mussels are now in the Tennessee and Cumberland River systems, the extent to which they will impact native mussels is unknown. However, as zebra mussels are likely to reach higher densities in the main stems, large tributaries, and below infested reservoirs, native mussels in these areas will likely be more heavily impacted than mussels in smaller streams without upstream reservoirs. Mussel extinctions are expected as a result of the continued spread of zebra mussels in the Eastern United States. Other potential threats from alien species on native mussels include the black carp (Mylopharyngodon piceus), a native of China. If these species invade Cumberlandian Region streams, they could wreak havoc on already stressed native mussel populations. The round goby (Neogobius melanostomus) is another alien invader fish species released in the 1980s into the Great Lakes in ballast waters originating in southeastern Europe. The arrival of round gobies may therefore have important indirect effects on unionid communities through negative impacts to their host fishes.

The overall threat to this species, posed by piscine and invertebrate predators, in most instances is not thought to be significant. Although parasitism is not thought to be a significant problem in mussels, excessive trematode infestations in their gonads have been implicated in inducing mussel senescence. The harvest of Cumberlandian Region mussel species for commercial purposes is well documented (Anthony and Downing, 2001). It is doubtful, however, that this species has ever been overly exploited for pearling, pearl buttons, cultured pearls, or any other exploitative activity (USFWS, 2004). The Clinch River population appears to be under imminent threat from sedimentation resulting from mountaintop removal coal mining within the watershed in Virginia (Williams et al., 2008).

Short-term Trend: Decline of >70%
Short-term Trend Comments: It has been extirpated from a large percentage of its former range (likely over 80%). TVA data indicates that populations continue to decline (USFWS, 2003; 2004). It has been eliminated from the mainstem of Tennessee and Cumberland Rivers and several tributaries and now restricted to five stream reaches (USFWS, 2003; 2004). In Alabama, the only known extant population is in a short (6 km) reach of Bear Creek, in the vicinity of Natchez Trace Parkway, Colbert Co., but it historically occurred in the Tennessee River across northern Alabama and some tributaries and just over the border in Tennessee in the Elk River (Williams et al., 2008). Hanlon et al. (2009) documented relict shells in Copper Creek (Upper Clinch) in Virginia.

Long-term Trend: Decline of 70-90%

Intrinsic Vulnerability: Highly to moderately vulnerable.
Intrinsic Vulnerability Comments: Without the level of genetic interchange these species experienced historically, many small and isolated populations that are now comprised predominantly of adult specimens may be slowly dying out due to various factors. This may, in part, account for the relatively recent demise of numerous tributary populations. Even given the improbable absence of the impacts from current and existing threats, smaller isolated populations of this species may be lost to the devastating consequences of below-threshold effective population size (EPS). Once-sizable populations of many Cumberlandian mussel species occurred throughout significant portions of the main stems of the large rivers and tributary systems comprising the Cumberlandian Region. This was particularly true for the Cumberlandian combshell and oyster mussel. Historically, there were no natural absolute barriers to genetic interchange among their tributary subpopulations and those of their host fishes (with the notable exception of Cumberland Falls. Without the level of genetic interchange these species experienced historically (because of anthropogenic threats), many small and isolated populations that are now comprised predominantly of adult specimens may be slowly dying out due to various factors (USFWS, 2004).

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.

Other NatureServe Conservation Status Information

Inventory Needs: Determine extent of existing populations and continue surveys for additional EOs.

Protection Needs: All populations should receive protection through acquisition, easement, registry, and working with local, state, and federal government agencies on issues relating to development, water quality, river designation, etc. In particular, management procedures and regulations to control pollution and siltation from upstream areas of the watershed are critical. Critical habitat proposed (USFWS, 2003; 2004).

Distribution
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Global Range: (250-1000 square km (about 100-400 square miles)) Historically, this species was distributed throughout the Cumberlandian region of the Tennessee and Cumberland river systems in Alabama, Kentucky, Mississippi, Tennessee, and Virginia (USFWS, 2003; 2004). Populations are currently known from Buck Creek in Kentucky; through a few miles of the Big South Fork Cumberland River in Kentucky and Tennessee; and in very low numbers in the Powell and Clinch rivers in Virginia and Tennessee (USFWS, 1997). A few, likely non-reproducing populations associated with sub-lotic sections of some reservoirs (e.g., Old Hickory Reservoir on the Cumberland River). In 1997 several fresh dead specimens were found by Jeff Garner in Bear Creek, a tributary of the Tennessee River in northwestern Alabama and according to Tom Mann (Mississippi Natural Heritage Program) fresh dead shells were found in Mississippi in September 2000 (see also McGregor and Garner, 2004). Currently, it is restricted to five stream reaches (USFWS, 2003; 2004). In Mississippi, it is found only in the Tennessee River drainage in extreme northeastern portion of state (Jones et al., 2005). In Alabama, the only known extant population is in a short (6 km) reach of Bear Creek, in the vicinity of Natchez Trace Parkway, Colbert Co. (Williams et al., 2008).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single nation

U.S. & Canada State/Province Distribution
United States AL, KY, MS, TN, VA

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
AL Colbert (01033), Franklin (01059)*, Lauderdale (01077)*, Lawrence (01079)*, Limestone (01083)*
KY Cumberland (21057)*, Laurel (21125)*, McCreary (21147), Pulaski (21199), Rockcastle (21203)*, Russell (21207)*, Wayne (21231)*
MS Tishomingo (28141)
TN Claiborne (47025), Davidson (47037)*, DeKalb (47041)*, Greene (47059), Hancock (47067), Lincoln (47103)*, Marshall (47117), Maury (47119)*, Putnam (47141)*, Scott (47151), Smith (47159)*, Trousdale (47169), Wilson (47189)
VA Lee (51105), Scott (51169), Washington (51191)*
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
05 Upper Cumberland (05130101)*, Rockcastle (05130102)+*, Upper Cumberland-Lake Cumberland (05130103)+, South Fork Cumberland (05130104)+, Upper Cumberland-Cordell Hull (05130106)*, Caney (05130108)+*, Lower Cumberland-Old Hickory Lake (05130201)+, Lower Cumberland-Sycamore (05130202)+*, Stones (05130203)*, Lower Cumberland (05130205)*, Red (05130206)*
06 North Fork Holston (06010101)+, South Fork Holston (06010102)*, Holston (06010104)*, Pigeon (06010106)*, Lower French Broad (06010107)*, Nolichucky (06010108)+, Watts Bar Lake (06010201)*, Lower Little Tennessee (06010204)*, Upper Clinch (06010205)+, Powell (06010206)+, Lower Clinch (06010207)*, Middle Tennessee-Chickamauga (06020001)*, Guntersville Lake (06030001)*, Wheeler Lake (06030002)+*, Upper Elk (06030003)+, Lower Elk (06030004)+*, Pickwick Lake (06030005)+*, Bear (06030006)+, Lower Tennessee-Beech (06040001)*, Upper Duck (06040002)+, Lower Duck (06040003)+*
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
U.S. Distribution by Watershed (based on multiple information sources) Help
Ecology & Life History
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Basic Description: A freshwater mussel that has a yellow to tawny brown shell with narrow green, broken rays.
General Description: Shell subquadangular (female) to subhomboid (male), solid, increasingly inflated with age; anterior end regularly rounded; ventral margin slightly curved; dorsal margins straight (male) to broadly curved (female); beaks elevated, wide, flattened, sculptured with feebly double-looped bars; posterior ridge well-developed, narrowly rounded; posterio-ventral area of female inflated and dilated to accomodate the expanded marsupia, separated from the rest of the shell by anterior and posterior sulci, margin of expansion may be semicircular or sulcate, growth lines in this area serrate, shell margin dentate; periostracum smooth to cloth-like, yellow to tawny brown with narrow green broken rays, rays may be quite numerous and often punctate particularly posteriorly. Two ragged triangular pseudocardinal teeth in left valve, single in right; interdentum short; lateral teeth heavy, short, tend to be curved, double in left valve, single in right; beak cavity shallow; anterior muscle scars confluent, small, deeply impressed; pallial line distinct; nacre white.
Diagnostic Characteristics: The broad, yellowish shell with broken rays and the distictive marsupial expansion of the female distinguish this species from most other mussels in its range except Ptychobranchus fasciolaris and Epioblasma lenior (Lea, 1842). Male Epioblasma brevidens are broader than P. fasciolarisand females of the latter species do not exhibit the marsupial development of the former. Raying patterns on P. fasciolaris usually are not as developed. E. lenior is a considerably smaller species, has a much lighter shell, tends to be greenish, does not have as developed a marsupial expansion, and is probably extinct.
Reproduction Comments: This species appears to be a long-termed brooder with spawning occurring in late summer and embryoinc stages/glochidia held in the branchial marsupia until late spring. Mussels have been observed to be in the process of discharging glochidia during late May and early June. During this time, the female mussels were observed to be either lying on the surface of the substrate or to have most of the shell extruded above the level of the substrate surface. In laboratory studies, six species of perciform fish have been identified to serve as glochidial hosts for this species: Etheostoma blennioides (greenside darter), Etheostoma maculatum (spotted darter), Etheostoma rufilineatum (redline darter), Etheostoma vulneratum (wounded darter), Etheostoma simotreum (snubnose darter), Percina caprodes (logperch), Cottus baileyi (black sculpin), Cottus bairdi (mottled sculpin), and Cottus carolinae (banded sculpin) (USFWS, 2003; 2004; Yeager and Saylor, 1995). Glochidia transformed to juvenile mussels after 16 - 45 days of encystment of these fish (Yeager, summarized in Hill, 1986).
Ecology Comments: Species of Epioblasma are true riffle species, being associated primarily with stream sections exhibiting high energy flows, high water quality, and rocky substrates (see GHABCOM). Little else is known ecologically of this species other than it formerly was fairly common throughout its geographic range. Some representative density values of surviving populations have been listed for the Clinch and Powell Rivers (0 - .38/sq. meter: Jenkinson and Ahlstedt, 1988).
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Mobility and Migration Comments: This species is probably rather sessile with limited movement in the substrate. Passive downstream movement may occur when mussels are displaced from the substrate during floods. Major dispersal occurs while glochidia are encysted on their hosts.
Riverine Habitat(s): BIG RIVER, MEDIUM RIVER, Moderate gradient, Riffle
Special Habitat Factors: Benthic
Habitat Comments: The habitat ranges from large creeks to large rivers, in substrates ranging from coarse sand to mixtures of gravel, cobble, and boulder-sized particles. The mussel tends to occur at depths of less than one meter, although the relict (and presumably non-reproducing) populations now occur in considerably deeper water (Gordon and Layzer, 1989). Inhabits medium-sized streams to large rivers on shoals and riffles in coarse sand, gravel, cobble, and boulders and is not associated with small stream habitats. Occurs in larger tributaries than Epioblasma capsaeformis (USFWS, 2003; 2004).
Adult Food Habits: Detritivore
Immature Food Habits: Parasitic
Food Comments: Larvae (glochidia) of freshwater mussles generally are parasitic on fish and display varying degrees of host specificity. No specific trophic studies have been conducted on this species. General literature claims that mussels are filter feeders which remove phytoplankton from the water column. These assumptions appear to be based on casual observations of mussels in situ and a few examinations of rectal contents. Baker (1928) speculated that detritus was the primary energy source. This has been substantiated by James (1987) and correlates well with microhabitats observed in the field. This suggests that mussels may occupy a variety of trophic guilds wuch as postulated for the SPHERIIDAE (see Lopez and Holopaien, 1987; Gordon and Layzer, 1989).
Phenology Comments: Little is known concerning phenology of mussles other than when eggs/glochidia are held in the branchial marsupia. Being poikilothermic, activity levels would expectedly be reduced greatly during cold temperature months.
Length: 8 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Stewardship Overview: Listed Endangered throughout its range, except in the free-flowing reach of the Tennessee River from the base of Wilson Dam downstream to the backwaters of Pickwick Reservoir and the lower 5 RM of all tributaries to this reach in Colbert and Lauderdale Counties, Alabama (Federal Register, 14 June 2001).

The USFWS, in cooperation with the State of Tennessee and Conservation Fisheries, Inc., proposes to reintroduce this species into its historical habitat in the free-flowing reach of the French Broad River below Douglas Dam to its confluence with the Holston River, Knox County Tennessee, and in the free-flowing reach of the Holston River below Cherokee Dam to its confluence with the French Broad River (Federal Register, 13 June 2006).

Recently, critical habitat was designated for the Duck River (0 river km occupied, 74 river km unoccupied habitat) in Tennessee, Bear Creek (40 river km occupied, 0 river km unoccupied habitat) in Alabama and Mississippi, Powell River (154 river km occupied, 0 river km unoccupied habitat) in Tennessee and Virginia, Clinch River (242 river km occupied, 0 river km unoccupied habitat) in Tennessee and Virginia, Nolichucky River (0 river km occupied, 8 river km unoccupied habitat) in Tennessee, Big South Fork (43 river km occupied, 0 river km unoccupied habitat) in Tennessee and Kentucky, and Buck Creek (58 river km occupied, 0 river km unoccupied habitat) in Kentucky (USFWS, 2004).

Recovery plan published (USFWS, 2004) with recovery objective: delisting.
Recovery Strategy: The preservation of extant populations and the occupied habitats of these five species is the most immediate and important recovery priority for these mussels. Preservation and protection of these populations will be achieved by continuing to use existing regulatory mechanisms, establishing partnerships with various stakeholders, using best management practices, and minimizing or eliminating threats to the species. Each extant population must also be viable to achieve recovery. Unless a previously unknown population is found, other viable populations within the historic range of each of the five species must be reestablished and protected to effect recovery. Reestablishing new viable populations will require close coordination with and concurrence of the State(s) involved and with other partners that have interests at any potential reintroduction sites. Additional research into the life history and ecological requirements of these mussels as defined in this plan will help formulate the biological information necessary for the preservation of existing or reestablishment and maintenance of other viable populations. Knowledge of the effective population size is particularly critical for determining the size and demographic makeup of a viable population for these species. Due to the rarity of extant populations, propagation of laboratory or hatchery-reared progeny is the most logical means of providing individuals for the establishment of new populations. Facilities that attempt to propagate these mussels should follow the Service's established controlled propagation policy. Priorities for recovery efforts for the five species via propagation should be to develop propagation technology, augment and expand the ranges of extant populations to ensure their viability, and reestablish viable populations in other streams within their historical range that have suitable habitat and water quality. Pursuing and implementing these efforts will enable the recovery of the five species.
Recovery Criteria: Downlisting from endangered to threatened status will occur when the following criteria are met for the protection of extant stream populations, discovery of currently unknown stream populations, and/or reestablishment of historical stream populations: (1) five streams with distinct viable populations of the Cumberland elktoe, six streams with distinct viable populations of the oyster mussel and Cumberlandian combshell, four streams with distinct viable populations of the purple bean, and three streams with distinct viable populations of the rough rabbitsfoot have been established; (2) one distinct naturally reproduced year class exists within each of the viable populations; (3) research studies of the mussels' biological and ecological requirements have been completed and any required recovery measures developed and implemented from these studies are beginning to be successful, as evidenced by an increase in population density of approximately 20 percent and/or an increase in the length of the river reach of approximately 10 percent inhabited by the species as determined through biennial monitoring; (4) no foreseeable threats exist that would likely impact the survival of the species over a significant portion of their ranges; (5) within larger streams the species are distributed over a long enough reach that a single catastrophic event is not likely to eliminate or significantly reduce the entire population in that stream to a status of nonviable; and (6) biennial monitoring of the five species yields the results outlined in criterion (1) above over a 10-year period.
Actions Needed:
1. Utilize existing legislation/regulations to protect current and newly discovered populations.
2. Determine the species' life history requirements and threats and reduce or alleviate those threats which threaten the species.
3. Develop and use an information/education program to solicit the assistance of local landowners, communities, and others to recover the species.
4. Search for additional populations, and through propagation activities, pursue augmentations or reintroductions in order to establish viable populations.
5. Conduct anatomical and molecular genetic analysis of the species to determine the potential occurrence of species complexes or hidden biodiversity.
6. Develop and implement a monitoring program, and annually assess the recovery program where needed.

Biological Research Needs: Determine the habitat preferences and environmental ranges, sensitivity to various pollutants, and if known glochidial hosts occur at all extant EOs. Possible re-examination of glochidial host may be necessary if the latter is negative and evidence of recent successful reproduction/recruitment is available.
Population/Occurrence Delineation
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Group Name: Freshwater Mussels

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance.

Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls.
Separation Distance for Unsuitable Habitat: 2 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: None
Separation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence.

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 28Apr2009
NatureServe Conservation Status Factors Author: Cordeiro, J.
Management Information Edition Date: 06Oct2005
Management Information Edition Author: Cordeiro, J.
Element Ecology & Life History Edition Date: 04Dec2006
Element Ecology & Life History Author(s): Cordeiro, J.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Ahlstedt, S.A. and J.M. Tuberville. 1997. Quantitative reassessment of the freshwater mussel fauna in the Clinch and Powell rivers, Tennessee and Virginia. Pages 72-97 in K.S. Cummings, A.C. Buchanan, C.A. Mayer, and T.J. Naimo, eds. Conservation and management of freshwater mussels II: initiatives for the future. Proceedings of a UMRCC symposium, 16-18 October 1995, St. Louis, Missouri. Upper Mississippi River Conservation Committee, Rock Island, Illinois.

  • Anthony, J.L. and J.A. Downing. 2001. Exploitation trajectory of a declining fauna: a century of freshwater mussel fisheries in North America. Canadian Journal of Fisheries and Aquatic Sciences, 58: 2071-2090.

  • Baker, F.C. 1928b. The freshwater Mollusca of Wisconsin: Part II. Pelecypoda. Bulletin of the Wisconsin Geological and Natural History Survey, University of Wisconsin, 70(2): 1-495.

  • Burch, J.B. 1975a. Freshwater unionacean clams (Mollusca: Pelecypoda) of North America. Malacological Publications: Hamburg, Michigan. 204 pp.

  • Gordon, M.E. and J.B. Layzer. 1989. Mussels (Bivalvia: Unionoidea) of the Cumberland River review of life histories and ecological relationships. U.S. Fish and Wildlife Service Biological Report, 89(15): 1-99.

  • Hill, D.M. 1986. Cumberlandian mollusk conservation program, activity 3: identification of fish hosts. Office of Natural Resources and Economic Development, Tennessee Valley Authority, Knoxville, Tennessee. 55 pp.

  • Howard, A.D. 1915. Some exceptional cases of breeding among the Unionidae. The Nautilus 29:4-11.

  • Isom, B.G., P. Yokley, Jr., and C.H. Gooch. 1973. Mussels of Elk River Basin in Alabama and Tennessee- 1965-1967. American Midland Naturalist 89(2):437-442.

  • James, M.R. 1987. Ecology of the freshwater mussel Hyridella menziesi in a small oliogotrophic lake. Archives of Hydrobiology 108:337-348.

  • Jenkinson, J.J. and S.A. Ahlsedt. 1988a. Quantitative reassessment of the freshwater mussel fauna in the Clinch River, Tennessee and Virginia. Tennessee Valley Authority, Knoxville, Tennessee. 28 pp.

  • Jenkinson, J.J. and S.A. Ahlstedt. 1988b. Quantitative reassessment of the freshwater mussel fauna in the Powell River, TN and VA. Tennessee Valley Authority, Knoxville, Tennessee. 28 pp.

  • Johnson, R.I. 1978. Systematics and zoogeography of Plagiola (= Dysnomia = Epioblasma), an almost extinct genus of freshwater mussels (Bivalvia: Unionidae) from middle North America. Bulletin of the Museum of Comparative Zoology, 148(6): 239-320.

  • Johnson, R.I. and H.B. Baker. 1973. Types of Unionacea (Mollusca:Bivalvia) in the Academy of Natural Sciences of Philadelphia. Proceedings of the Academy of Natural Sciences of Philadelphia, 125: 146-186.

  • Jones, R.L., W.T. Slack, and P.D. Hartfield. 2005. The freshwater mussels (Mollusca: Bivalvia: Unionidae) of Mississippi. Southeastern Naturalist, 4(1): 77-92.

  • Lefevre, G. and W.T. Curtis. 1912. Studies on the reproduction and artificial propogation of fresh-water mussels. Bulletin of the Bureau of Fisheries 30:102-201.

  • Lopez, G.R. and I.J. Holopainen. 1987. Interstitial suspension-feeding by Pisidium spp. (Pisidiiae: Bivalvia): a new guild in lentic benthos? American Malacological Bulletin, 5: 21-29.

  • McGregor, S.W. and J.T. Garner. 2004. Changes in the freshwater mussel (Bivalvia: Unionidae) fauna of the Bear Creek system of northwest Alabama and northeast Mississippi. American Malacological Bulletin, 18(1/2): 61-70.

  • Mirarchi, R.E., J.T. Garner, M.F. Mettee, and P.E. O'Neil. 2004b. Alabama wildlife. Volume 2. Imperiled aquatic mollusks and fishes. University of Alabama Press, Tuscaloosa, Alabama. xii + 255 pp.

  • Moyle, P. and J. Bacon. 1969. Distribution and abundance of molluscs in a fresh water environment. Journal of the Minnesota Academy of Science 35(2/3):82-85.

  • Parmalee, P.W. and A.E. Bogan. 1998. The freshwater mussels of Tennessee. University of Tennessee Press, Knoxville, Tennesee. 328 pp.

  • Strayer, D. 1983. The effects of surface geology and stream size on freshwater mussel (Bivalvia, Unionidae) distribution in southeastern Michigan, U.S.A. Freshwater Biology 13:253-264.

  • Strayer, D.L. 1999a. Use of flow refuges by unionid mussels in rivers. Journal of the North American Benthological Society 18(4):468-476.

  • Strayer, D.L. and J. Ralley. 1993. Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia) including two rare species of Alasmidonta. Journal of the North American Benthological Society 12(3):247-258.

  • Turgeon, D.D., J.F. Quinn, Jr., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, R.J. Neves, C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland: 526 pp.

  • U.S. Fish and Wildlife Service (USFWS). 1997. Determination of Endangered Status for the Cumberland Elktoe, Oyster Mussel, Cumberlandian Combshell, Purple Bean, and Rough Rabbitsfoot. Final rule. Federal Register, 62(7): 1647-1658.

  • U.S. Fish and Wildlife Service (USFWS). 1998. Cumberland elktoe (Alasmidontaq atropurpurea), oyster mussel (Epioblasma capsaeformis), Cumberlandian combshell (Epioblasma brevidens), purple bean (Villosa perpurpurea), and rough rabbitsfoot (Quadrula cylindrica strigillata): Technical Draft Recovery Plan. U.S. Fish and Wildlife Service: Asheville, North Carolina. 119 pp.

  • U.S. Fish and Wildlife Service (USFWS). 2001. Endangered and Threatened Wildlife and Plants; establishment of nonessential experimental population status for 16 freshwater mussels and 1 freshwater snail (Anthony's Riversnail) in the free-flowing reach of the Tennessee River below the Wilson Dam, Colbert and Lauderdale Counties, Alabama. Federal Register, 66(115): 32250-32264.

  • U.S. Fish and Wildlife Service (USFWS). 2003. Endangered and Threatened Widlife and plants; proposed designation of critical habitat for five threatened mussels in the Tennessee and Cumberland River basins; proposed rule. Federal Register, 68(106): 33234-33282

  • U.S. Fish and Wildlife Service (USFWS). 2004. Recovery plan for Cumberland elktoe, oyster mussel, Cumberlandian combshell, purple bean, and rough rabbitsfoot. U.S. Fish and Widlife Service, Atlanta, Georgia. 168 pp.

  • U.S. Fish and Wildlife Service (USFWS). 2006. Endangered and threatened wildlife and plants; establishment of nonessential experimental population status for 15 freshwater mussels, 1 freshwater snail, and 5 fishes in the lower French Broad River and in the lower Holston River, Tennessee; Proposed Rule. Federal Register, 71(113): 34195-34230.

  • Van der Schalie, H. 1938a. The naiad fauna of the Huron River in southeastern Michigan. Miscellaneous Publication of the Museum of Zoology, University of Michigan 40:7-78.

  • Watters, G.T. 1992a. Unionids, fishes, and the species-area curve. Journal of Biogeography 19:481-490.

  • Wells, S.M., R.M. Pyle, and N.M. Collins. 1983. The IUCN Invertebrate Red Data Book. IUCN, Gland, Switzerland. 632 pp.

  • Williams, J. D., A. E. Bogan, R. S. Butler, K. S. Cummings, J. T. Garner, J. L. Harris, N. A. Johnson, and G. T. Watters. 2017. A revised list of the freshwater mussels (Mollusca: Bivalvia: Unionida) of the United States and Canada. Freshwater Mollusk Biology and Conservation 20:33-58.

  • Williams, J. D., A. E. Bogan, and J. T Garner. 2008. Freshwater mussels of Alabama & the Mobile Basin in Georgia, Mississippi, & Tennessee. University of Alabama Press, Tuscaloosa, Alabama. 908 pages.

  • Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993b. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9): 6-22.

  • Yeager, B.L. and C.F. Saylor. 1995. Fish hosts for four species of freshwater mussels (Pelecypoda: Unionidae) in the Upper Tennessee River drainage. American Midland Naturalist, 133(1): 1-6.

References for Watershed Distribution Map
  • Barr, W.C., S.A. Ahlstedt, G.D. Hickman, and D.M. Hill. 1993-1994. Cumberlandian mollusk conservation program. Activity 8: Analysis of macrofauna factors. Walkerana 7(17/18):159-224.

  • Biological Resources Division, USGS. 1997. Database of museum records of aquatic species. Compiled by J. Williams (USGS-BRD, Gainesville, FL).

  • Hanlon, S.D., M.A. Petty, and R.J. Neves. 2009. Status of native freshwater mussels in Copper Creek, Virginia. Southeastern Naturalist 8(1):1-18.

  • Hubbs, D. 2002. Monitoring and management of endangered mussels. 2001-02 Annual Report Project 7365, Tennessee Wildlife Resources Agency, Nashville, Tennessee. 3 pp.

  • Parmalee, P.W. and A.E. Bogan. 1998. The Freshwater Mussels of Tennessee. University of Tennessee Press: Knoxville, Tennessee. 328 pp.

  • U.S. Fish and Wildlife Service (USFWS). 2004. Endangered and Threatened Widlife and plants; designation of critical habitat for five endangered mussels in the Tennessee and Cumberland River basins; final rule. Federal Register, 69(168): 53135-53180.

  • Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater Mussels of Alabama & the Mobile Basin in Georgia, Mississippi & Tennessee. University of Alabama Press: Tuscaloosa, Alabama. 908 pp.

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