Pleurobema sintoxia - (Rafinesque, 1820)
Round Pigtoe
Synonym(s): Quadrula paupercula (Simpson, 1900)
Taxonomic Status: Accepted
Related ITIS Name(s): Pleurobema coccineum (Conrad, 1834) (TSN 80087) ;Pleurobema sintoxia (Rafinesque, 1820) (TSN 568107)
French Common Names: pleurobčme écarlate
Unique Identifier: ELEMENT_GLOBAL.2.109664
Element Code: IMBIV35070
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Pleurobema
Genus Size: D - Medium to large genus (21+ species)
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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: Pleurobema sintoxia
Taxonomic Comments: Recently, Oesch (1984) introduced the combination Pleurobema sintoxia (Rafinesque, 1820) as the senior synonym of Pleurobema coccineum (Conrad, 1836). Oesch did not provide any discussion or justification in resurrecting the Rafinesque name.

The members of the genus Pleurobema are among the most difficult to identify in North America. Arguments arise even among taxonomists regarding the "species" represented in the genus Pleurobema. Stansbery (1983) summarized many of the problems and identified a few of the shell characters used to separate P. sintoxia from the morphologically similar and often co-occurring P. plenum, P. cordatum, and P. rubrum. A few "morphs" have been variously identified and named but no rigorous genetic, anatomic, or conchologic study has ever been published on this group to help elucidate species boundaries or relationships.ema sintoxia from the morphologically similar and often co-occurring Pleurobema plenum, Pleurobema cordatum, and Pleurobema rubrum. A few "morphs" have been variously identified and named but no rigorous genetic, anatomic, or conchologic study has ever been published on this group to help elucidate species boundaries or relationships.
Conservation Status
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NatureServe Status

Global Status: G4G5
Global Status Last Reviewed: 12May2009
Global Status Last Changed: 24May2007
Rounded Global Status: G4 - Apparently Secure
Reasons: The large river populations have become increasingly rare. Distribution is greatly fragmented but remains relatively wide, much as it was historically. Long-term viability of many populations is questionable, especially those in large rivers where zebra mussel populations are now established; but outside these areas the species appears to maintain stable populations.
Nation: United States
National Status: N4N5 (24May2007)
Nation: Canada
National Status: N1 (01Aug2017)

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), Arkansas (S3), Illinois (SNR), Indiana (S3), Iowa (S1), Kansas (S2), Kentucky (S4S5), Michigan (S3), Minnesota (S3), Missouri (S4), Nebraska (SNR), New York (S1), Ohio (S3), Oklahoma (S4?), Pennsylvania (S3S4), South Dakota (S1), Tennessee (S4), West Virginia (S2), Wisconsin (S3)
Canada Ontario (S1)

Other Statuses

Canadian Species at Risk Act (SARA) Schedule 1/Annexe 1 Status: E (14Jul2005)
Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Endangered (02May2014)
Comments on COSEWIC: Reason for designation: This mussel species occupies a small area in the Lake St. Clair watershed and three other watersheds in southern Ontario, where its habitat has been declining in extent and quality. Urban development, agricultural runoff, and impacts from the Zebra Mussel and the Round Goby are threatening the survival of the species in Canada.

Status history: Designated Endangered in May 2004. Status re-examined and confirmed in May 2014.

IUCN Red List Category: LC - Least concern
American Fisheries Society Status: Currently Stable (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 200,000-2,500,000 square km (about 80,000-1,000,000 square miles)
Range Extent Comments: This species was historically distributed from New York and Ontario west to South Dakota, Kansas and Oklahoma, and south to Louisiana and Alabama. Large river populations largely eliminated in the upper Midwest, but many populations still survive in Mississippi River tributaries. The current distribution of the Round Pigtoe is similar to the historical range. Although large river populations have for the most part disappeared from the upper Midwest, many populations still survive in tributaries of the Mississippi and Ohio rivers. In Canada Pleurobema sintoxia is only known from southern Ontario (COSEWIC, 2004) including the Thames River (Cudmore et al., 2004). Recently this species has been confirmed to be nearly extirpated (last live specimens probably do not represent a viable population) in the main channel of the Detroit River between Lake St. Clair and Lake Erie, Michigan/Ontario; due to zebra mussel invasion (Schloesser et al., 2006). Long-standing population exist in the Poteau River and tributaries, Arkansas and Oklahoma (Vaughn and Spooner, 2004).

Area of Occupancy: >12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 81 to >300
Number of Occurrences Comments: In Pennsylvania, it is in 12 sites in the Allegheny (Little Mahoning Creek- Chapman and Smith, 2008), 14 in the French Creek, and 2 in the Lake Erie drainage. In New York, it is widespread in the Allegheny basin, but likely gone from the Niagara basin. There are several records throughout West Virginia (nowhere in abundance) in the Monongahela and Little Kanawha River drainages, Elk, Kanawha, Ohio Rivers, and Middle Island Creek. It is not common in Indiana (Muscatatuck- Harmon, 1989; Tippecanoe- Cummings and Berlocher, 1990; St. Joseph- Pryor, 2005) and Illinois (Mackinaw, Kankakee, Sangamon, Embarras River drainages (Cummings and Mayer, 1997; Schanzle and Cummings, 1991; Sietman et al., 2001), but is widespread in the Mississippi and Ohio drainages; recently Fox basin in Illinois and Wisconsin (Schanzle et al., 2004). In Ohio, it was widespread (Watters, 1992; 1995) but has declined with only a few recent records: St. Joseph and tribs. in Williams Co., Olentangy, Big Darby, Little Darby, Caesar Creeks, Walhonding River, lower Muskingum River, and western basin of Lake Erie (Watters et al., 2009). In Tennessee, it is restricted to the Cumberland, Big South Fork Cumberland, and Stones rivers (Parmalee and Bogan, 1998) including Muscle Shoals region (Tennessee/Alabama) again in 2001. In Alabama, it is rare (Wilson and Guntersville Dam tailwaters) but was historic through the Tennessee River (Mirarchi, 2004; Williams et al., 2008). It is in Kentucky in the S Fork Kentucky (Evans, 2008), Middle Green and Barren Rivers (Cochran and Layzer, 1993), but in the Green River eastward (Cicerello and Schuster, 2003; Gordon, 1991); also Ohio River (not widespread nor abundant), upper Green and major tribs., Rolling Fork (Salt River trib.), upper Cumberland River's major tribs., and Big Sandy River. Oklahoma distribution (as P. cordatum): Chikaskia (as P. coccineum), Little, Kiamichi, Verdigris (Boeckman and Bidwell, 2008), Neosho, Poteau, Mountain Fork, and Spring Rivers (Branson, 1966; 1983) into Missouri, but N occurrences likely P. sintoxia; a small population in the Red River. In Kansas, range includes the Neosho, Verdigris, Elk, Fall, Spring, and Marais des Cygnes Rivers but scattered (Couch, 1997); historical in Wakarusa (Tiemann, 2006); ongoing work on the Verdigris (Miller and Lynott, 2006). In the Big Blue system of SE Nebraska and NE Kansas, it was historically rare in Kansas (1 museum plus 1 from Delaware River); but not over a century (Hoke, 2005). Recently only dead shells in the Marais des Cygnes, Elk, and Fall Rivers in Kansas (Combes and Edds, 2005). It was recently collected in Poteau (Vaughn and Spooner, 2004), St. Francis (Ahlstedt and Jenkinson, 1991), Cache and White Rivers, Arkansas (Christian, 1995; Christian et al., 2005). It is relatively common in Missouri, in 13 major drainages throughout the S half (Oesch, 1995); but little recruitment (MO DOC 359 records from 1977-1999, 79% live/ fresh dead). It has not been seen in recent surveys of Iowa, but reported historically. It has not been found alive recently in Presque Isle Bay or Thompson Bay (outer harbour of Presque Isle Bay). In Michigan, it is fairly widespread in the Great Lakes and Ohio River drainages (incl. Clinton River drainage- Trdan and Hoeh, 1993), but seldom common, but still persists in Lake St. Clair (COSEWIC, 2004; Strayer, 1980) incl. Pine (Badra and Goforth, 2003). In Canada in the Thames River, in 8 of 16 sites in a 150 km reach in 1997-1998 and historically broadly distributed, but now limited to the upper reaches of the Middle Thames near Thamesford and upstream to near the S Thames confluence (Cudmore et al., 2004). It also occurs in Ontario's Sydenham River (Metcalfe-Smith et al., 2003). Recently confirmed nearly extirpated (last live specimens probably not viable) in the main channel Detroit River between Lake St. Clair and Lake Erie, Michigan/Ontario; due to zebra mussel invasion (Schloesser et al., 2006).

Population Size: 100,000 to >1,000,000 individuals
Population Size Comments: Many healthy populations are still extant in the upper Mississippi River drainage. Due to problems obtaining a unbiased and complete sample, abundance in mussels is difficult to estimate, and no estimates of population size or abundance have been made. Smith and Crabtree (2010) found this species at 7 of 32 sites (1 with recruitment) along the entire length of Pennsylvania's French Creek.

Number of Occurrences with Good Viability/Integrity: Some to many (13-125)
Viability/Integrity Comments: In Canada in the Thames River, shells were found in eight sites (of 16) in an approximately 150 km reach of the river in 1997-1998 and this, along with historic collections from widely separated sites, suggests the species was once broadly distributed in the river, but it is now limited to a very small population in the upper reaches of the Middle Thames near Thamesford and just upstream of Thamesford down to near the Confluence with the South Thames (Cudmore et al., 2004). This species occurs as a viable population (juveniles present) in Muddy Creek (French Creek drainage) in the Erie NWR in Crawford Co., Pennsylvania (Mohler et al., 2006). Kentucky maintains several good populations (Cicerello and Schuster, 2003).

Overall Threat Impact: High
Overall Threat Impact Comments: Smith (1971) ranked the causes of extirpation or declines in fish species as follows: siltation, drainage of bottomland lakes, swamps, and prairie marshes, desiccation during drought, species introductions, pollution, impoundments, and increased water temperatures. All of these factors render habitats unsuitable, cause extirpations, and lead to the isolation of populations thereby increasing their vulnerability to extirpation for many aquatic species (including mussels) throughout North America. Zebra mussels, Dreissena polymorpha, have destroyed mussel populations in the Great Lakes and significantly reduced mussels in many of the large rivers of eastern North America. Zebra mussels have the potential to severely threaten other populations especially if they make their way into smaller streams. Pollution through point (industrial and residential discharge) and non-point (siltation, herbicide and fertilizer run-off) sources is perhaps the greatest on-going threat to this species and most freshwater mussels. Lowered dissolved oxygen content and elevated ammonia levels (frequently associated with agricultural runoff and sewage discharge) have been shown to be lethal to some species of freshwater naiads (Horne and McIntosh, 1979). Residential, mineral and industrial development also pose a significant threat. Rotenone, a toxin used to kill fish in bodies of water for increased sport fishery quality, has been shown to be lethal to mussels as well (Heard, 1970). Destruction of habitat through stream channelization and maintenance and the construction of dams is still a threat in some areas. Impoundments reduce currents that are necessary for basic physiological activities such as feeding, waste removal and reproduction. In addition, reduced water flow typically results in a reduction in water oxygen levels and a settling out of suspended solids (silt, etc.), both of which are detrimental. Dredging of streams has an immediate effect on existing populations by physically removing and destroying individuals. Dredging also affects the long-term recolonization abilities by destroying much of the potential habitat, making the substrates and flow rates uniform throughout the system. Natural predators include raccoons, otter, mink, muskrats, turtles and some birds (Simpson, 1899; Boepple and Coker, 1912; Evermann and Clark, 1918; Coker et al., 1921; Parmalee, 1967; Snyder and Snyder, 1969). Domestic animals such as hogs can root mussel beds to pieces (Meek and Clark, 1912). Fishes, particularly catfish, ICTALURUS SPP. and AMIEURUS SPP., and freshwater drum, APLODINOTUS GRUNNIENS, also consume large numbers of unionids. See the General Freshwater Mussel ESA. The introduction and spread of the exotic Zebra Mussel (Dreissena polymorpha) throughout the Great Lakes drainage has led to dramatic declines of native freshwater mussels in colonized areas. Zebra Mussels have infested 63% of sites where P. sintoxia was known to occur prior to 1990. The Zebra Mussel invasion of Lake St. Clair, Lake Erie and the Detroit and Niagara rivers has led to the reduction or elimination of P. sintoxia and other native mussel species from these waters. Zebra Mussels may threaten the population of Round Pigtoes that still survives in the delta area of Lake St. Clair, as it is not known if the unionid community is stable or if the process of extirpation by Zebra Mussels is just slower in this area. P. sintoxia in Ontario, i.e., the population in the Sydenham River, because the river is not navigable by boats and has few impoundments that could support a permanent colony. Nevertheless, the reservoirs at Coldstream and Strathroy in the headwaters of the East Sydenham River are of some concern (from COSEWIC, 2004).

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Large river populations are exceedingly rare in the upper Midwest. Recent information suggests that the current distribution and abundance of the Round Pigtoe in the U.S. is generally the same as it was historically, although declines seem evident in a number of areas. Overall, the Round Pigtoe has been lost from about 54% of its former range (in terms of extent of occurrence) in Canada; the historical extent of occurrence was 26,592 km2 and the current EO is 12,360 km2, with an estimated area of occupancy of about 15 km2 (COSEWIC, 2004). In Minnesota, Sietman (2003) reports this species has recently expanded above St. Anthony Falls on the Mississippi River. Some declines have been noted in Illinois (Schanzle et al., 2004). In Canada, only remnant populations still occur in Lakes Erie and St. Clair and it is represented by a few relic specimens in the Grand and Thames Rivers; it is also declining in the Sydenham River and St. Clair delta, Ontario (Metcalfe-Smith and Cudmore-Vokey, 2004).

Long-term Trend: Decline of <50% to Relatively Stable
Long-term Trend Comments: It was extirpated from the Black River, Ohio, over 100 years ago (Lyons et al., 2007). It is likely extirpated from the Wakarusa basin in Kansas (Tiemann, 2006). In Alabama, it is known historically from the Tennessee River across the northern part of the state and the Paint Rock River but is currently confined to the tailwaters of Guntersville and Wilson Dams on the Tennessee River (Williams et al., 2008).

Intrinsic Vulnerability: Not intrinsically vulnerable

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity Comments: This species is somewhat sensitive to pollution, siltation, habitat perturbation, inundation, and loss of glochidial hosts. This species is found in medium to large rivers in mixed mud, sand, and gravel (Cummings and Mayer, 1992). In Canada, the Round Pigtoe is typically found in medium-sized to large rivers but also occurs in Lake Erie and Lake St. Clair (COSEWIC, 2004). Parmalee and Bogan (1998) reported Tennessee occurrences most abundantly, and almost exclusively, in medium-sized and big rivers and in current on a firm substrate of coarse gravel and sand at depths of less than three feet to more than 20 feet.

Other NatureServe Conservation Status Information

Inventory Needs: Largely because of the problems in identification and species relationships, the southern populations of the genus are questionable both in regards to identity and status. An inventory with the expressed purpose of collecting specimens and preserving them for genetic study is needed.

Distribution
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Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) This species was historically distributed from New York and Ontario west to South Dakota, Kansas and Oklahoma, and south to Louisiana and Alabama. Large river populations largely eliminated in the upper Midwest, but many populations still survive in Mississippi River tributaries. The current distribution of the Round Pigtoe is similar to the historical range. Although large river populations have for the most part disappeared from the upper Midwest, many populations still survive in tributaries of the Mississippi and Ohio rivers. In Canada Pleurobema sintoxia is only known from southern Ontario (COSEWIC, 2004) including the Thames River (Cudmore et al., 2004). Recently this species has been confirmed to be nearly extirpated (last live specimens probably do not represent a viable population) in the main channel of the Detroit River between Lake St. Clair and Lake Erie, Michigan/Ontario; due to zebra mussel invasion (Schloesser et al., 2006). Long-standing population exist in the Poteau River and tributaries, Arkansas and Oklahoma (Vaughn and Spooner, 2004).

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: occurs (regularly, as a native taxon) in multiple nations

U.S. & Canada State/Province Distribution
United States AL, AR, IA, IL, IN, KS, KY, MI, MN, MO, NE, NY, OH, OK, PA, SD, TN, WI, WV
Canada ON

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
AL Colbert (01033), Lauderdale (01077), Limestone (01083), Madison (01089), Marshall (01095), Morgan (01103)
AR Ashley (05003), Baxter (05005), Benton (05007), Bradley (05011), Clark (05019), Clay (05021), Cleveland (05025), Conway (05029), Cross (05037), Dallas (05039), Fulton (05049), Grant (05053), Hot Spring (05059), Howard (05061), Independence (05063), Izard (05065), Jackson (05067), Lawrence (05075), Little River (05081), Madison (05087), Marion (05089), Mississippi (05093), Monroe (05095), Montgomery (05097), Nevada (05099), Newton (05101), Ouachita (05103), Poinsett (05111), Prairie (05117), Randolph (05121), Saline (05125), Scott (05127), Searcy (05129), Sevier (05133), Sharp (05135), St. Francis (05123), Stone (05137), Van Buren (05141), Washington (05143), White (05145), Woodruff (05147), Yell (05149)
IA Allamakee (19005), Cerro Gordo (19033), Clayton (19043), Clinton (19045), Dubuque (19061), Floyd (19067), Franklin (19069), Hamilton (19079), Hardin (19083), Johnson (19103), Muscatine (19139), Sac (19161), Scott (19163), Webster (19187)
IN Harrison (18061), Spencer (18147), Vanderburgh (18163)
KS Allen (20001), Bourbon (20011), Cherokee (20021), Coffey (20031), Cowley (20035), Elk (20049), Franklin (20059), Greenwood (20073), Labette (20099), Linn (20107), Lyon (20111), Marion (20115), Miami (20121), Montgomery (20125), Neosho (20133), Wilson (20205), Woodson (20207)
MI Allegan (26005), Barry (26015), Berrien (26021), Branch (26023)*, Calhoun (26025), Cass (26027), Clare (26035)*, Clinton (26037), Dickinson (26043), Eaton (26045), Genesee (26049), Gratiot (26057), Hillsdale (26059), Huron (26063)*, Ingham (26065), Ionia (26067), Jackson (26075), Kalamazoo (26077), Kent (26081), Lapeer (26087)*, Lenawee (26091), Livingston (26093), Macomb (26099), Manistee (26101)*, Mecosta (26107)*, Menominee (26109), Midland (26111), Missaukee (26113), Monroe (26115), Newaygo (26123)*, Oakland (26125), Osceola (26133), Ottawa (26139)*, Saginaw (26145), Sanilac (26151), Shiawassee (26155), St. Clair (26147), St. Joseph (26149), Tuscola (26157), Van Buren (26159), Washtenaw (26161), Wayne (26163)
MN Anoka (27003), Blue Earth (27013), Brown (27015), Carver (27019), Chippewa (27023), Chisago (27025), Dakota (27037), Faribault (27043), Goodhue (27049), Hennepin (27053), Houston (27055), Jackson (27063), Kanabec (27065), Lac Qui Parle (27073), Martin (27091), Mower (27099), Nicollet (27103), Olmsted (27109), Pine (27115), Ramsey (27123), Redwood (27127), Renville (27129), Rice (27131), Scott (27139), Steele (27147), Stevens (27149), Swift (27151), Wabasha (27157), Washington (27163), Watonwan (27165), Winona (27169), Yellow Medicine (27173)
NY Cattaraugus (36009), Chautauqua (36013), Erie (36029)
OH Ashtabula (39007), Coshocton (39031), Defiance (39039), Fairfield (39045), Franklin (39049), Hancock (39063), Knox (39083), Lake (39085), Lucas (39095), Madison (39097), Marion (39101), Morgan (39115), Pickaway (39129), Putnam (39137), Trumbull (39155), Union (39159), Warren (39165), Washington (39167), Williams (39171)
OK Craig (40035), Nowata (40105), Ottawa (40115)
PA Armstrong (42005), Clarion (42031), Crawford (42039), Erie (42049), Forest (42053), Greene (42059), Indiana (42063), Lawrence (42073), McKean (42083), Mercer (42085), Potter (42105), Venango (42121), Warren (42123)
WV Cabell (54011), Mason (54053), Monongalia (54061), Ritchie (54085), Wood (54107)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
04 Menominee (04030108)+, St. Joseph (04050001)+, Black-Macatawa (04050002)+*, Kalamazoo (04050003)+, Upper Grand (04050004)+, Maple (04050005)+, Lower Grand (04050006)+, Thornapple (04050007)+, Muskegon (04060102)+, Betsie-Platte (04060104)+*, Pine (04080202)+, Shiawassee (04080203)+, Flint (04080204)+*, Cass (04080205)+, Lake Huron (04080300)+*, St. Clair (04090001)+, Lake St. Clair (04090002)+, Clinton (04090003)+, Detroit (04090004)+, Huron (04090005)+, Ottawa-Stony (04100001)+*, Raisin (04100002)+, St. Joseph (04100003)+, Upper Maumee (04100005)+, Tiffin (04100006)+, Auglaize (04100007)+, Blanchard (04100008)+, Lower Maumee (04100009)+, Grand (04110004)+, Chautauqua-Conneaut (04120101)+, Niagara (04120104)+, Lake Erie (04120200)+*
05 Upper Allegheny (05010001)+, Conewango (05010002)+, Middle Allegheny-Tionesta (05010003)+, French (05010004)+, Middle Allegheny-Redbank (05010006)+, Lower Monongahela (05020005)+, Shenango (05030102)+, Mahoning (05030103)+*, Beaver (05030104)+*, Connoquenessing (05030105)+, Upper Ohio-Shade (05030202)+, Little Kanawha (05030203)+, Hocking (05030204)+, Mohican (05040002)+, Walhonding (05040003)+, Muskingum (05040004)+, Upper Scioto (05060001)+, Raccoon-Symmes (05090101)+, Little Miami (05090202)+, Silver-Little Kentucky (05140101)+*, Blue-Sinking (05140104)+, Lower Ohio-Little Pigeon (05140201)+, Highland-Pigeon (05140202)+
06 Wheeler Lake (06030002)+, Pickwick Lake (06030005)+
07 Twin Cities (07010206)+, Upper Minnesota (07020001)+, Pomme De Terre (07020002)+, Hawk-Yellow Medicine (07020004)+, Chippewa (07020005)+, Redwood (07020006)+, Middle Minnesota (07020007)+, Cottonwood (07020008)+, Blue Earth (07020009)+, Watonwan (07020010)+, Le Sueur (07020011)+, Lower Minnesota (07020012)+, Upper St. Croix (07030001)+, Kettle (07030003)+, Snake (07030004)+, Lower St. Croix (07030005)+, Rush-Vermillion (07040001)+, Cannon (07040002)+, Buffalo-Whitewater (07040003)+, La Crosse-Pine (07040006)+, Root (07040008)+, Coon-Yellow (07060001)+, Grant-Little Maquoketa (07060003)+, Copperas-Duck (07080101)+, Upper Cedar (07080201)+, Shell Rock (07080202)+, Upper Iowa (07080207)+, Lower Iowa (07080209)+, Des Moines Headwaters (07100001)+, Upper Des Moines (07100002)+, Middle Des Moines (07100004)+, Boone (07100005)+, North Raccoon (07100006)+
08 Lower St. Francis (08020203)+, Little River Ditches (08020204)+, Lower White-Bayou Des Arc (08020301)+, Cache (08020302)+, Ouachita Headwaters (08040101)+, Upper Ouachita (08040102)+, Little Missouri (08040103)+, Lower Ouachita-Smackover (08040201)+, Upper Saline (08040203)+, Lower Saline (08040204)+
10 Boyer (10230007)+, Upper Marais Des Cygnes (10290101)+, Lower Marais Des Cygnes (10290102)+, Little Osage (10290103)+
11 Beaver Reservoir (11010001)+, Middle White (11010004)+, Buffalo (11010005)+, Upper Black (11010007)+, Current (11010008)+, Lower Black (11010009)+, Spring (11010010)+, Strawberry (11010012)+, Upper White-Village (11010013)+, Little Red (11010014)+, Lower Walnut River (11030018)+, Upper Verdigris (11070101)+, Fall (11070102)+, Middle Verdigris (11070103)+, Neosho headwaters (11070201)+, Upper Cottonwood (11070202)+, Lower Cottonwood (11070203)+, Upper Neosho (11070204)+, Middle Neosho (11070205)+, Lake O' the Cherokees (11070206)+, Spring (11070207)+, Illinois (11110103)+, Poteau (11110105)+, Lake Conway-Point Remove (11110203)+, Petit Jean (11110204)+, Fourche La Fave (11110206)+, Lower Little (11140109)+
+ 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 highly variable freshwater mussel; relatively large, rounded or elongate, chestnut or brown, with a shallow beak cavity.
General Description: SHELL EXTERIOR: Shell moderately thick, round, and compressed (medium-sized rivers) to inflated (large rivers). Anterior end rounded, posterior end rounded to bluntly pointed. Dorsal margin straight to slightly curved, ventral margin usually curved. Umbos low and only slightly elevated above the hinge line. Beak sculpture of two to three elevated ridges on the umbo. Shell smooth, periostracum greenish brown, light brown or reddish brown in juveniles, becoming chestnut or dark brown in adults, with faint green rays visible near the beaks in some shells. Length to four inches.

SHELL INTERIOR: Pseudocardinal teeth well developed; two in the left valve, one in the right. Lateral teeth straight. Beak cavity moderate (large river) to shallow (medium-sized rivers). Nacre variable from white to pink or rose colored. (Cummings and Mayer, 1992)

Diagnostic Characteristics: In Canada the Round Pigtoe may be confused with the Wabash Pigtoe (Fusconaia flava). The main features distinguishing F. flava from P. sintoxia are a lower and more centrally located beak, deeper lateral sulcus, and deeper beak cavity in F. flava. The lake form of P. sintoxia is somewhat similar to Obovaria olivaria, but has flatter valves, a duller periostracum, and is less likely to have coloured rays (COSEWIC, 2004).

Reproduction Comments: Pleurobema sintoxia is believed to be sexually dioecious, but is not sexually dimorphic. The lifespan of P. sintoxia has not yet been determined, but other members of the Subfamily Ambleminae are known to live for more than 30 years. Age to maturity for this species is not known, but the juvenile stage for most unionids lasts 2-5 years. The Round Pigtoe is a short-term brooder (tachytictic) with the breeding season lasting from early May to late July in Wisconsin (Parmalee and Bogan 1998). The glochidia are subovate, without hooks, measuring 150 µm in both height and width according to Clarke (1981) and 160 µm according to Hoggarth (1992). The lack of hooks suggests that they are gill parasites. Early reported hosts include the bluegill (Lepomis macrochirus) (Surber, 1913; Coker et al., 1921). Recently identified host fishes for this mussel are the spotfin shiner (Cyprinella spiloptera), bluntnose minnow (Pimephales notatus), northern redbelly dace (Phoxinus eos), and southern redbelly dace (Phoxinus erythrogaster) (Hove, 1995; Hove et al., 1997). New host fish confirmations wer identified from Watters et al. (2005): central stoneroller (Campostoma anomalum), bluegill (Lepomis macrochirus), creek chub, southern redbelly dace (Phoxinus erythrogaster).
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): BIG RIVER, MEDIUM RIVER, Pool, Riffle
Lacustrine Habitat(s): Deep water, Shallow water
Special Habitat Factors: Benthic
Habitat Comments: This species is found in medium to large rivers in mixed mud, sand, and gravel (Cummings and Mayer, 1992). In Canada, the Round Pigtoe is typically found in medium-sized to large rivers but also occurs in Lake Erie and Lake St. Clair (COSEWIC, 2004). Parmalee and Bogan (1998) reported Tennessee occurrences most abundantly, and almost exclusively, in medium-sized and big rivers and in current on a firm substrate of coarse gravel and sand at depths of less than three feet to more than 20 feet.
Adult Food Habits: Planktivore
Food Comments: Round Pigtoes, like all species of freshwater mussels, are filter feeders as adults. Their primary food sources are bacteria, algae, particles of organic detritus, and some protozoans. Food availability may be a limiting factor for the Lake St. Clair population due to the presence of high densities of Zebra Mussels, which are also filter-feeders. During the parasitic larval stage, glochidia feed on the body fluids of the host (COSEWIC, 2004).
Length: 1.2 centimeters
Economic Attributes Not yet assessed
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Management Summary
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Biological Research Needs: In order to effectively manage mussel species it is necessary to work out certain life history characteristics first. Because of their unusual life-cycle and dependence on fish for completion of that cycle, it is imperative that the host species for the round pigtoe be ascertained. Life history studies need to be done to identify age and size at sexual maturity, recruitment success, age class structure, and other important life history parameters.

Research is needed to assess the success of watershed protection on mussel populations. Abundance and distribution of selected species needs to be monitored in order to ascertain how species abundances change over time. From that we can assess what land-use changes, conservation practices, and physical/chemical parameters are correlated with, and possibly responsible for, the biological changes.

As was stated in the taxonomic section above, this is an extremely difficult genus to identify. Arguments arise even among taxonomists regarding the "species" represented in the genus PLEUROBEMA. Although a few "morphs" have been variously identified and named, no rigorous genetic, anatomic, or conchologic study has ever been published on this group to help elucidate species boundaries or relationships.

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: 12May2009
NatureServe Conservation Status Factors Author: Cordeiro, J. (2009); Cummings, K.S. (2nd edition); Whittaker, J.C. (1998)
Element Ecology & Life History Edition Date: 28Feb2007
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).

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References for Watershed Distribution Map
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