Villosa perpurpurea




STATUS: On January 10, 1997, the purple bean was designated as Endangered throughout its entire range (USFWS 1997).  A draft recovery plan addressing the purple bean is awaiting final approval (USFWS 2003).  Please note: When finalized, the recovery plan should be reviewed to determine if any changes have been made in occurrence or habitat.


SPECIES DESCRIPTION:   The purple bean has a small to medium‑sized shell.  The periostracum is usually dark brown to black with numerous closely spaced fine green rays.  The nacre is purple, but the purple may fade to white in dead specimens.  See Bogan and Parmalee (1983) and Parmalee and Bogan (1998) for a more complete description of the species and Parmalee and Bogan (1998) for a synonymy of the species. Gordon (1991) provided diagnostic characters.


Freshwater mussel adults are filter‑feeders, positioning themselves in substrates to facilitate siphoning of the water column for oxygen and food (Kraemer 1979). Their food includes primarily detritus, plankton, and other microorganisms (Fuller 1974).  Juvenile mussels employ foot (pedal) feeding, and are thus suspension feeders (Yeager et al. 1994).  Foods of juvenile freshwater mussels up to two weeks old include bacteria, algae, and diatoms with amounts of detrital and inorganic colloidal particles (Yeager et al. 1994).  Specific food habits of the purple bean are unknown, but are likely similar to those of other freshwater mussels.


REPRODUCTION AND DEVELOPMENT:   Gravid females of the lampsiline purple bean have been observed in January and February (Ahlstedt 1991a; Butler, pers. obs., 2001), and they release their glochidia in May and June (Watson 1999).  The smallest gravid individual found in a study in Indian Creek was 1.5 inches (Watson 1999).  The length of the glochidia is 0.005 inch, and the width is 0.007 inch (Watson 1999).  At least four host fish species have been identified – the fantail darter (Etheostoma flabellare), greenside darter, black sculpin, and mottled sculpin and/or banded sculpin (Watson and Neves 1996, Watson 1999; Jones, letter dated June 9, 2003).  Transformation took from 11 to 25 days, at 70.7° to 76.1°F.


RANGE AND POPULATION LEVEL:  The purple bean is endemic to the upper Tennessee River system above its confluence with the Clinch River (Table 4, USFWS 2003). ( Its type locality was stated simply as “Tennessee”; therefore, the type locality is not included in Table 4.)  Primarily a species of the Ridge and Valley Physiographic Province, it also occurs at the eastern edge of the Cumberland Plateau.  The entire range of the purple bean occurs in northeastern Tennessee and southwestern Virginia.


The purple bean has apparently been extirpated from the Powell River, North Fork Holston River, Emory River, Daddys Creek, and North Fork Beech Creek (Table 4, USFWS 2003).  Extant populations are located in isolated portions of the Clinch River, Tazewell, Russell, and Scott Counties, Virginia; Indian Creek, Tazewell County, Virginia; Copper Creek, Scott County, Virginia; Obed River, Cumberland County, Tennessee; and Beech Creek, Hawkins County, Tennessee (Table 4, USFWS 2003).  A recent quantitative study by Ahlstedt and Tuberville (1997) in the Clinch River in Tennessee and Virginia revealed this species to be “rare” over the 15‑year sampling period.  Periodic sampling (approximately 5‑year intervals) of at least 345 quadrats from 11 to 14 sites in the Clinch revealed densities of 0.11 per square foot in both 1979 and 1988, but no specimens were taken during 1994.


Currently, the largest population may have occurred in the upper Clinch River and Indian Creek metapopulation (Ahlstedt, pers. comm., 1997), prior to a Clinch River chemical spill in late 1998 that resulted in the death of at least 52 specimens.  Watters (1999) found 26 live purple bean specimens in Indian Creek in 1996‑97, which represented 2 percent of the entire mussel fauna.  The population probably numbers in the hundreds and is probably viable, as evidenced by the presence of individuals that were probably juveniles (0.9 inch in length).  Neves (1991) considered the Copper Creek population to be the largest, but that population has been decimated in recent years.  Fraley and Ahlstedt (2000) found only two live specimens and a single fresh dead shell during their 1998 qualitative resurvey of Copper Creek (see Ahlstedt 1981a).  The status of the Emory River system population is tenuous.  It remains at six sites in the Obed River but in very low numbers (Ahlstedt et al. 2001).  Its viability status is questionable (Ahlstedt, pers. comm., 2003).  The Beech Creek population, the only extant purple bean population in the Holston River system, was sampled in February 2001.  A total of 74 live specimens were found; most were exposed on the substrate while apparently attracting host fish (S. J. Fraley, TVA, unpub. data [currently with the North Carolina Wildlife Resources Commission]).  Live individuals were located at 9 of 12 Beech Creek sites sampled, and evidence of recent recruitment was observed.  Beech Creek probably harbors the largest and healthiest remaining purple bean population rangewide.  However, it appears tenuous, because riparian development and agricultural impacts are prevalent in the watershed ®. S. Butler, pers. obs., 2001).  This purple bean population is also thought to be declining (Ahlstedt, pers. comm., 2001).


HABITAT: This species inhabits small headwater streams (Neves 1991) to medium‑sized rivers (Gordon 1991).  It is found in moderate to fast‑flowing riffles with sand, gravel, and cobble substrates (Neves 1991) and rarely occurs in deep pools or slack water (Ahlstedt 1991a).  It is sometimes found out of the main current adjacent to water‑willow beds and under flat rocks (Ahlstedt 1991a, Gordon 1991).


PAST THREATS: The abundance and distribution of the purple bean decreased historically from human-induced habitat loss and degradation (Williams et al. 1993, Neves 1993) caused by impoundments, sedimentation and turbidity, channelization, and contaminants contained in numerous point and nonpoint sources.   A comprehensive review of these past threats is provided elsewhere (USFWS 2003, Williams et al. 1993, Neves 1993, Neves 1991, Neves et al. 1997, Watters 2000, Richter et al. 1997).  These habitat changes have resulted in significant extirpations (localized loss of populations), restricted and fragmented distributions, and poor recruitment of young.


Numerous Cumberlandian Region streams have experienced mussel kills from toxic chemical spills and other causes (Cairns et al. 1971, Crossman et al. 1973, Neves 1986, Wolcott and Neves 1994).  The high number of jeopardized species in the upper Tennessee River system make accidental spills a particular concern to conservationists and resource managers (Hampson et al. 2000).  The dramatic impact the chlor‑alkali chemical plant in Saltville, Virginia, has had on the aquatic fauna in the North Fork Holston River is well documented (Adams 1915; Cairns et al. 1971; Stansbery and Clench 1974; Hill et al. 1975; Ahlstedt 1980, 1991c; Neves and Zale 1982; Sheehan et al. 1989; Hampson et al. 2000).  Although it is considered a chronic episode, and not an “event” like most other toxic spills, it is discussed in this section simply because of the tremendous impact it has had on the river.


Since the plant’s opening in 1893, mercury and various salts (e.g., calcium chloride, sodium chloride) from this site have polluted the North Fork Holston River and decimated the entire molluscan fauna all the way to the mouth of the river, a distance of 80 miles (Ahlstedt 1991b).  Occurring in this river reach were populations of the purple bean, rough rabbitsfoot, Cumberlandian combshell, oyster mussel, and 34 other mussel species (Neves and Zale 1982).  From 1950 to 1971, an estimated 75 pounds of mercury per day were discharged from this facility directly into the North Fork or into unlined floodplain holding ponds (Hampson et al. 2000).  The long‑term kill was so thorough that only one mussel species was reported in the early 1970s by Hill et al. (1975).


The closing of the plant in 1972 brought about the possible opportunity for natural mussel recolonization in the North Fork Holston River (Stansbery and Clench 1974).  Efforts were soon made to help speed up the recovery of mussels in the North Fork. However, the lingering effects of mercury, extremely low numbers of mussels, and possibly low numbers of fish hosts may be responsible for the general lack of mussels observed at sites within 20 miles downstream of Saltville (Henley and Neves 1995).


An alkaline fly ash pond spill in 1967 and a sulfuric acid spill in 1970 on the Clinch River at the power plant at Carbo, Virginia, caused a massive mussel kill for up to 12 miles downstream from the power plant site (Cairns et al. 1971, Crossman et al. 1973, Stansbery 1986, Sheehan et al. 1989, Wilcove and Bean 1994).  Populations of the purple bean, rough rabbitsfoot, Cumberlandian combshell, and oyster mussel that may have resided in the affected river reach were undoubtedly impacted by these spill events.  Natural recolonization has not occurred in the impacted river reach (Stansbery 1986, Ahlstedt 1991a, Hampson et al. 2000), possibly due to copper contamination from the power plant at Carbo (Wilcove and Bean 1994).  An experimental reintroduction of nonlisted mussels in 1981 and 1984 has largely failed (Sheehan et al. 1989).


An overturned tanker truck resulted in a chemical spill in the upper Clinch River on August 27, 1998, killing more than 7,000 mussel specimens of 16 species.  Approximately 250 specimens of three federally listed species were found dead over a 5.5‑mile reach, including at least 52 purple bean specimens and 20 rough rabbitsfoot specimens (Jones et al. 2001).  According to Ahlstedt (1983), “hundreds of dead shells were observed buried in the substratum” during a 1980 Elk River survey.  He attributed this kill to an unknown chemical spill.


CURRENT THREATS:  The purple bean and its habitat is currently being impacted by excessive sediment bed loads of smaller sediment particles, changes in turbidity, increased suspended solids (primarily resulting from nonpoint‑source loading from poor land‑use practices, lack of best management practices [BMPs], and maintenance of existing BMPs), and pesticides.  Other primarily localized impacts include coal mining, gravel mining, reduced water quality below dams, developmental activities, water withdrawal, impoundments, and alien species.  Their restricted ranges and low population levels also increase their vulnerability to toxic chemical spills and the deleterious effects of genetic isolation.


Coal mining activities occur in portions of the upper Powell and Clinch River systems, primarily in Virginia.  Scores of active and inactive mines are known from these drainages (Hampson et al. 2000).  The role that coal mining has played in the decline of mussel fauna in the Powell River in Virginia was prophesied by Ortmann (1918) and has been briefly summarized by Wolcott and Neves (1990, 1994).  Five mine tailings pond spills were reported from 1995 to 1999 in the upper Clinch and Powell River systems (Hampson et al. 2000), at least one of which resulted in a major fish kill (Koch, pers. comm., 1996).  Research by Kitchel et al. (1981) indicates that Powell River mussel populations were inversely correlated with coal fines in the substrate.  When coal fines were present, decreased filtration times and increased movements were noted in laboratory‑held mussels (Kitchel et al. 1981).


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 (Hampson et al. 2000).  In fact, Hampson et al. (2000) detected 29 different PAHs in stream sediment samples in the two watersheds.  The Clinch River at Pendleton Island had concentrations of two measured PAHs, naphthalene and phenanthrene, at 400 micrograms per kilogram (µg/kg) and 570 µg/kg, respectively, both of which are above the protection guidelines for aquatic life.  The Canadian probable‑effect levels of 391 µg/kg and 515 µg/kg, respectively, have been established for these compounds.  The probable‑effect levels define concentrations above which adverse effects to aquatic organisms can be expected.  Pendleton Island was once a stronghold for the rough rabbitsfoot and home to the purple bean, Cumberlandian combshell, and oyster mussel as well in the early 1980s (Ahlstedt 1991a).  However, the fauna there was in marked decline less than a decade later.  Three other sites in the Clinch River system (i.e., lower Clinch River, Guest River, Copper Creek) had concentrations of these two compounds below the probable‑effect levels.  A site on the Powell River near Arthur, Tennessee, had much higher levels of naphthalene and phenanthrene (1,600 µg/kg and 1,300 µg/kg, respectively) than at Pendleton Island.   In the Emory River, downstream of a population of the purple bean in the Obed River, excessive napthalene levels were detected (610 ug/kg).  Mining activities also likely contributed to the extirpation of the purple bean from the Powell River several decades ago.


Sediment from the upper Clinch River, where this species occurs, was found to be toxic to juvenile mussels (Robison et al. 1996).  Ahlstedt and Tuberville (1997) speculated that the presence of toxins in the Clinch River may explain the decline and lack of mussel recruitment at some sites in the Virginia portion of that stream.  Wilcove and Bean (1994) reported that studies indicated that mussel reproduction below the site of the Appalachian Power Company’s (APCO) electric generating station in Carbo, Virginia, was being inhibited by copper discharges.  In addition, copper was shown to be toxic to mussels at levels below the U.S. Environmental Protection Agency (EPA) criteria established in Virginia.  The Virginia State Water Control Board began proceedings to impose a special water quality standard for copper below the plant.  In 1992, the State and APCO agreed on a lower standard for copper for this specific stretch of the Clinch.  APCO is spending several million dollars to control copper discharge from its facility to meet the new standard (Wilcove and Bean 1994).


Although the Clean Water Act (CWA), administered by the EPA, has helped eliminate many point‑source effluents, “straight pipes” (pipelines conveying untreated household effluents; e.g., chlorine, detergents, household chemicals, human waste, etc., from rural homes directly into streams) continue to discharge wastes.  Fraley and Ahlstedt (2000) thought that effluents from straight pipes were partially to blame for the documented decline of the native mussel fauna in Copper Creek from 19 species in 1980 to 11 species in 1998.  Included in the historical Copper Creek fauna were the purple bean, rough rabbitsfoot, and oyster mussel, although only a few of these species were found live in 1998.  Numerous other streams in the Cumberlandian Region doubtless also have straight pipes discharging pollutants into mussel habitat.




Exposure Scenario Summary Table for the Purple Bean




Life Stage





















contact with

water, diet


fish body



fantail darter, greenside darter, black sculpin, mottled sculpin and/or banded sculpin








contact & ingestion of

water, diet,



filter feeder


algae, detritus,








Adams, C. C.  1915.  The variations and ecological distribution of the snails of the genus Io.  National Academy of Sciences.  Volume XII, 2nd Memoir.  92 pp.


Ahlstedt, S. A.  1980.  Recent mollusk transplants into the North Fork Holston River in southwestern Virginia.  Bulletin of the American Malacological Union, Inc., for 1979:21‑23.


------.  1981.  The molluscan fauna of Copper Creek (Clinch River system) in southwestern Virginia.  Bulletin of the American Malacological Union, Inc., for 1981:4‑6.


------.  1983.  The molluscan fauna of the Elk River in Tennessee and Alabama.  American Malacological Bulletin 1:43‑50.


------.  1991a.  Twentieth century changes in the freshwater mussel fauna of the Clinch River (Tennessee and Virginia).  Walkerana 5(13):73‑122.


------.  1991b.  Cumberlandian Mollusk Conservation Program:  mussel surveys in six Tennessee Valley streams.  Walkerana 5(13):123‑160.


------.  1991c.  Reintroduction of the spiny riversnail Io fluvialis (Say, 1825) (Gastropoda:  Pleuroceridae) into the North Fork Holston River, southwest Virginia and northeast Tennessee.  American Malacological Bulletin 8(2):139‑142.


Ahlstedt, S. A., and J. M. Tuberville.  1997.  Quantitative reassessment of the freshwater mussel fauna in the Clinch and Powell Rivers, Tennessee and Virginia.  Pp. 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, October 1995, St. Louis, Missouri.  Upper Mississippi River Conservation Committee, Rock Island, Illinois.


Ahlstedt, S. A., J. F. Connell, S. Bakaletz, and M. T. Fagg.  2001.  Freshwater mussels of the National Park Service Obed Wild and Scenic River.  Unpublished report, National Park Service, Oneida, Tennessee.  40 pp.


Bogan, A. E., and P. W. Parmalee.  1983.  Tennessee’s rare wildlife, Volume II:  the mollusks.  Tennessee Wildlife Resources Agency, Nashville.  123 pp.


Cairns, J., Jr., J. S. Crossman, K. L. Dickman, and E. E. Herrick.  1971.  Chemical plants leave unexpected legacy in two Virginia rivers.  Science 198:1015‑1020.


Crossman, J. S., J. Cairns, Jr., and R. L. Kaesler.  1973.  Aquatic invertebrate recovery in the Clinch River following hazardous spills and floods.  Virginia Polytechnic Institute Water Resources Research Center Bulletin No. 63.  66 pp.


Fraley, S. J., and S. A. Ahlstedt.  2000.  The recent decline of the native mussels (Unionidae) of Copper Creek, Scott County, Virginia.  Pp. 189‑195 in:  P. D. Johnson and R. S. Butler, eds.  Freshwater Mollusk Symposia Proceedings‑‑Part II:  Proceedings of the First Symposium of the Freshwater Mollusk Conservation Society, Chattanooga, Tennessee, March 1999.  Ohio Biological Survey, Columbus.


Fuller, S. L. H.  1974.  Clams and mussels (Mollusca:  Bivalvia).  Pp. 215‑273 in:  C. W. Hart, Jr., and S. L. H. Fuller, eds.  Pollution ecology of freshwater invertebrates.  Academic Press, New York.


Gordon, M. E.  1991.  Species accounts for Cumberland elktoe (Alasmidonta atropurpurea), oyster mussel (Epioblasma capsaeformis), Cumberlandian combshell (Epioblasma brevidens), purple bean (Villosa perpurpurea), and rough rabbitsfoot (Quadrula cylindrica strigillata).  Unpublished report, The Nature Conservancy, Boston.  75 pp.


Hampson, P. S., M. W. Treece, Jr., G. C. Johnson, S. A. Ahlstedt, and J. F. Connell.  2000.  Water quality in the upper Tennessee River basin, Tennessee, North Carolina, Virginia, and Georgia 1994‑98.  U.S. Geological Survey Circular 1205.  32 pp.


Henley, W. F., and R. J. Neves.  1999.  Recovery status of freshwater mussels (Bivalvia:  Unionidae) in the North Fork Holston River, Virginia.  American Malacological Bulletin 15(1):65‑73.


Hill, D. H., E. A. Taylor, and C. F. Saylor.  1975.  Status of faunal recovery in the North Fork Holston River, Tennessee and Virginia.  Proceedings of the Annual Conference of Southeastern Game and Fish Commissioners 28:398‑413.


Jones, J. W., R. J. Neves, M. A. Patterson, C. R. Good, and A. DiVittorio.  2001.  A status survey of freshwater mussel populations in the Upper Clinch River, Tazewell County, Virginia.  Banisteria 17:18‑30.


Kitchel, H. E., J. C. Widlak, and R. J. Neves.  1981.  The impact of coal‑mining waste on endangered mussel populations in the Powell River, Lee County, Virginia.  Unpublished report to the Virginia State Water Control Board, Richmond.  26 pp. 


Kraemer, L. R.  1979.  Corbicula (Bivalvia:  Sphaeriacea) vs. indigenous mussels (Bivalvia:  Unionacea) in U.S. rivers:  a hard case for interspecific competition?  American Zoologist 19:1085‑1096.


Neves, R. J.  1986.  Recent die‑offs of freshwater mussels in the United States:  an overview.  Pp. 7‑18 in:  R. J. Neves, ed.  Proceedings of a workshop, June 23‑25, 1986, on die‑offs of freshwater mussels in the United States.  Davenport, Iowa.


------.  1991.  Mollusks.  Pp. 251‑319 in:  K. Terwilliger, coordinator.  Virginia’s endangered species.  Proceedings of a symposium.  McDonald & Woodward Publishing Co., Blacksburg, Virginia.


------.  1993.  A state‑of‑the unionid address.  Pp. 1‑10 in:  K. S. Cummings, A. C. Buchanan, and L. M. Koch, eds.  Conservation and management of freshwater mussels.  Proceedings of a UMRCC symposium, October 1992, St. Louis, Missouri.  Upper Mississippi River Conservation Committee, Rock Island, Illinois.

Neves, R. J., A. E. Bogan, J. D. Williams, S. A. Ahlstedt, and P. W. Hartfield.  1997.  Status of aquatic mollusks in the southeastern United States:  a downward spiral of diversity.  Pp. 43‑85 in:  G. W. Benz and D. E. Collins, eds.  Aquatic fauna in peril:  the southeastern perspective.  Special Publication 1, Southern Aquatic Research Institute, Chattanooga, Tennessee.


Neves, R. J., and A. V. Zale.  1982.  Freshwater mussels (Unionidae) of Big Moccasin Creek, southwestern Virginia.  The Nautilus 96(2):52‑54.


Ortmann, A.E.  1918.  The nayades (freshwater mussels) of the upper Tennessee drainage with notes on synonymy and distribution.  Proceedings of the American Philosophical Society 77:521‑626.


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


Richter, B. R., D. P. Braun, M. A. Mendelson, and L. L. Master.  1997.  Threats to imperilled freshwater fauna.  Conservation Biology 11:1081‑1093.


Robison, W. A., S. R. Alexander, T. Hibner, and M. Wilson.  1996.  Clinch River Project:  sediment contaminants in the lower Clinch River.  Unpublished report, U.S. Department of the Interior, Fish and Wildlife Service, Cookeville, Tennessee.  52 pp.


Sheehan, R. J., R. J. Neves, and H. E. Kitchel.  1989.  Fate of freshwater mussels transplanted to formerly polluted reaches of the Clinch and North Fork Holston Rivers, Virginia.  Journal of Freshwater Ecology 5(2):139‑149.


Stansbery, D. H.  1986.  Distribution and relative abundance of unionid mollusks at Carbo, Virginia.  Unpublished report to the Appalachian Power Company, Carbo, Virginia.


Stansbery, D.H., and W.J. Clench.  1974.  The Pleuroceridae and Unionidae of the North Fork Holston River above Saltville, Virginia.  Bulletin of the American Malacological Union, Inc., for 1973:33-36.


U.S. Fish and Wildlife Service.  1997.  Endangered and threatened wildlife and plants; determination of Cumberland elktoe (Alasmidonta atropurpurea), oyster mussel (Epioblasma capsaeformis), Cumberlandian combshell (Epioblasma brevidens), purple bean (Villosa perpurpurea), and rough rabbitsfoot (Quadrula cylindrica strigillata) to be endangered species.  Federal Register 62(7):1647‑1658.


U.S. Fish and Wildlife Service.  2003.  Agency Draft Recovery Plan for Cumberland Elktoe, Oyster Mussel, Cumberlandian Combshell, Purple Bean, and Rough Rabbitsfoot.  Atlanta, Georgia.  167 pp.


Watson, B. T.  1999.  Population biology and fish hosts of several federally endangered freshwater mussels (Bivalvia:  Unionidae) of the upper Tennessee River drainage, Virginia and Tennessee.  Unpublished M.S. Thesis, Virginia Polytechnic Institute and State University, Blacksburg.  124 pp.


Watson B. T., and R. J. Neves.  1996.  Host fishes for two federally endangered species of mussels.  Unpublished report in Triannual Unionid Report 10:13.


Watters, G.T.  2000.  Freshwater mollusks and water quality:  effects of hydrologic and instream habitat alterations. Pp. 261‑274 in:  R. A. Tankersley, D. Warmolts, G. T. Watters, B. Armitage, P. D. Johnson, and R. S. Butler, eds.  Freshwater Mollusk Symposia Proceedings‑‑Special Contribution:  Freshwater Mollusks as Indicators of Water Quality.  U.S. Geological Survey workshop, March 1997, Atlanta, Georgia.  Ohio Biological Survey, Columbus.

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


Wilcove, D. S., and M. J. Bean, editors.  1994.  The big kill:  declining biodiversity in America’s lakes and rivers.  Unpublished report, Environmental Defense Fund, Washington, D.C.  275 pp.


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


Wolcott, L. T., and R. J. Neves.  1990.  Impacts of siltation on the mussel fauna of the Powell River, Virginia.  Unpublished report to the U.S. Fish and Wildlife Service, Asheville, North Carolina.  116 pp.


------.  1994.  Survey of the freshwater mussels of the Powell River, Virginia.  Banisteria 3:3‑14.


Yeager, M. M., D. S. Cherry, and R. J. Neves.  1994.  Feeding and burrowing behaviors of juvenile rainbow mussels, Villosa iris (Bivalvia:  Unionidae).  Journal of the North American Benthological Society 13(2):217‑222.