Paetulunio

{{Short description|Species of bivalve}} {{Speciesbox | image = Usfws-femalerayedbean-usfws-angelaboyerjpg-large.jpg | status = EN | status_system = IUCN3.1 | status_ref = <ref name=IUCN>{{cite iucn |author=Cordeiro, J. |year=2012 |title=''Villosa fabalis'' |volume=2012 |article-number=e.T22973A2783483 |doi=10.2305/IUCN.UK.2012.RLTS.T22973A2783483.en |access-date=15 September 2025}}</ref> | status2 = G2 | status2_system = TNC | status2_ref = <ref name=natureserve>{{Cite NatureServe |title=''Paetulunio fabalis'' |id=2.116088 |access-date=15 September 2025 }}</ref> | parent_authority = Watters, 2018 | display_parents = 2 | taxon = Paetulunio fabalis | authority = ([[Isaac Lea|Lea]], 1831) | synonyms = * ''Villosa fabalis'' <small>(Lea, 1831)</small> }}

'''''Paetulunio fabalis''''', the '''rayed bean''', is a [[species]] of [[freshwater mussel]] in the family [[Unionidae]], the river mussels.<ref name=WoRMS/> It is the only species in the genus '''''Paetulunio''''',<ref>{{cite WoRMS |title=''Paetulunio'' Watters, 2018 |year=2025 |id=1056332 |db=MolluscaBase |access-date=15 September 2025}}</ref> and was formerly classified in ''[[Villosa]]'' until a 2018 study.<ref name=WoRMS>{{cite WoRMS |title=''Paetulunio fabalis'' (I. Lea, 1831) |year=2025 |id=1056333 |db=MolluscaBase |access-date=15 September 2025}}</ref><ref>{{Cite web |title=MUSSELpdb {{!}} valid gen. Paetulunio species |url=https://mussel-project.uwsp.edu/fmuotwaolcb/validgen_1627.html |access-date=2023-09-21 |website=mussel-project.uwsp.edu}}</ref>

The species name is derived from Latin, with a general meaning of "small crescent bean".

It was first described as ''Unio fabalis'' by [[Isaac Lea]] in 1831, from a specimen from the [[Ohio River]].

==Distribution== This species lives in eastern North America. It is native to the drainages of the [[Ohio River]], the [[Tennessee River]], and [[Lake Erie]] and [[Lake St. Clair]].

Currently, it is thought to occur in [[Michigan]], [[Indiana]], [[Ohio]], [[Pennsylvania]], [[New York (state)|New York]], [[Kentucky]], [[West Virginia]], and [[Ontario]]. In Canada, it is only known from the [[Sydenham River (Lake St. Clair)|Sydenham River]], with a small population in the north [[Thames River (Ontario)|Thames River]]. To the south and west, it occurs as far as the [[Maumee River]] watershed in Indiana and the [[Duck River (Tennessee)|Duck River]] in Tennessee. To the east, it occurs as far as the [[Elk River (West Virginia)|Elk River]] in West Virginia and the [[Allegheny River]] in Pennsylvania and New York. Shells have been found from the [[St. Joseph River (Lake Michigan)|St. Joseph River]] of [[Lake Michigan]], but it no longer exists in this watershed.

It has been extirpated from [[Lake Erie]], where it once lived in shallow shores and around [[Pelee Island|islands]], and the [[Detroit River]], due to invasive [[zebra mussel|zebra]] and [[quagga mussel|quagga]] mussels.<ref name=cosewic>{{cite web|url=https://www.canada.ca/en/environment-climate-change/services/species-risk-public-registry/cosewic-assessments-status-reports/rayed-bean-2010.html|title=Rayed bean (Villosa fabalis): COSEWIC assessment and status report 2010|author= Committee on the Status of Endangered Wildlife in Canada|access-date=31 August 2024}}</ref>

[[File:Usfws-rayed-bean-mussel-shell-display-large.jpg|thumb|left|Distinct wavy rays on the shell]]

==Description== The rayed bean is a small mussel that is rarely larger than 3.8 cm (1.5 in) in length. The shell is shiny and green, yellowish-green, or brown, and has many wavy, dark green rays. The rays may be obscured in older animals. The shell is thick and solid. The [[nacre]] is silvery-white or bluish and iridescent towards the posterior side. On the inside of the shell, it has unusually heavy teeth (structures along the inner hinge line) for a small mussel.

Females are generally smaller than males, and more inflated.<ref name=fws>{{cite web|url=https://ecos.fws.gov/ecp/species/5862|title=Species profile for rayed bean|author=USFWS|access-date=30 August 2024}}</ref>

==Habitat== It lives in small rivers and creeks with gravel or sandy [[riffle]]s, pools, or flats, and sometimes in the shallow areas of lakes. It prefers flowing water in shallow depths and may often be found buried around the roots of vegetation such as [[Dianthera americana|water willow]] and [[water milfoil]].<ref name=cosewic /> The rayed bean is almost always found buried in the substrate, at depths up to 15cm.<ref name=habitatuse>{{cite thesis | last=Grabarkiewicz | first=Jeff | title=Habitat Use and Community Structure of Unionid Mussels in Three Lake Erie Tributaries | date=2012 | doi=10.13140/RG.2.1.2256.7762 | type=MSc Thesis |publisher=University of Toledo }}</ref>

[[File:Usfws-rayed-bean-mussel-burrows-gravel-large.jpg|thumb|right|Rayed bean with a byssal thread attached to rock]]

Both adults and juveniles create [[byssus|byssal threads]] made of protein to anchor themselves to gravel or other objects in the water. Due to their small size, this adaptation helps them stay in suitable habitat without being swept away by the current.<ref name=cosewic />

==Ecology== Freshwater mussels in general are filter-feeders that [[siphon (mollusc)|siphon]] oxygen and food such as [[phytoplankton]] and [[microorganisms]] from the water. As juveniles they use "foot feeding" to absorb particles through their [[Mollusca#foot|foot]].

During reproduction, males release sperm into the water, which the females take in through their siphon. The female develops the eggs inside her gills. The number of eggs is likely in the thousands. The rayed bean is thought to be a long-term brooder, meaning they hold the developing eggs for several months. Brooding females have been found from May to October. Like most freshwater mussels, the [[glochidia]] (larvae) have a parasitic phase where they must attach to a host fish. To attract a host fish, the female rayed bean gapes her shell and exposes her white swollen gills that contain the glochidia. She moves papillae on her [[mantle (mollusc)|mantle]] in rhythmic, zipping motion. Presumably, like similar unionid mussels, when the fish comes near or nibbles her mantle, she will spurt glochidia into the water so that they can attach to the fish's skin and gills.

The only known host fish for the larval stage are the [[Etheostoma tippecanoe|Tippecanoe darter]] and the [[spotted darter]]. Other darters have been suggested as possible hosts as well, such as [[greenside darter]], [[rainbow darter]], [[mottled sculpin]], or [[largemouth bass]]. After spending 1–2 weeks attached to the fish's gills, the larvae finish metamorphosing and drop off as juvenile mussels.<ref name=fwsstatus>{{cite web|url=https://ecos.fws.gov/ServCat/DownloadFile/223846|title=Species Status Assessment Report for the Rayed Bean|author=USFWS|access-date=30 August 2024}}</ref>

Its lifespan has been estimated at around 20 years.<ref name=fwsstatus />

==As a food source== The rayed bean has been found in shell [[middens]] at Native American archaeological sites in small percentages. It was not likely preferred food due to its small size.<ref name=bogan>{{cite journal | last=Bogan | first=Arthur E. | title=Stability of Recent Unionid (Mollusca: Bivalvia) Communities Over the Past 6000 Years | journal=The Paleontological Society Special Publications | volume=5 | date=1990 | issn=2475-2622 | doi=10.1017/S2475262200005463 | pages=112–136}}</ref>

The species is preyed upon by [[muskrat]], [[racoon]], [[mink]], [[North American river otter|river otter]], [[striped skunk]], feral hogs, [[hellbender]] salamander, turtles, aquatic birds, and some fish.<ref name=fwsdetermination />

==Threats== The main threats to the rayed bean are siltation of rivers, water pollution, and changes in river flow and physical barriers imposed by [[dam]]s. Invasive dreissenid mussels ([[zebra mussel|zebra]] and [[quagga mussel|quagga]] mussels), and the invasive [[round goby]] also have a major impact.

===Habitat loss and alteration=== In 2012, it was estimated that the rayed bean had been eliminated from 73% of its historical habitat, leaving only highly fragmented populations.

[[File:Kinzua Dam, July 2015.jpg|thumb|left|[[Kinzua Dam]] on the Allegheny River, Pennsylvania]]

Dams cause dramatic change to [[riffle]] and [[shoal]] habitats, change flood patterns and water flow, and cause increased sedimentation. Dams block the free passage of host fish, preventing fish from reaching mussel populations, which is detrimental to mussel reproduction.<ref name=fwsdetermination /> In Ontario, dams cut off the North Thames population from their historic habitat in the south river.

Navigation channels, dredging, agricultural run-off, and livestock trampling of river edges cause sedimentation and disrupt mussel habitat. In Ontario, siltation from agricultural and forestry practices are the biggest threat to the species. Excessive silt can impact mussels' feeding and respiration and cause suffocation.<ref name=cosewic /> Much of the rayed bean's river habitat is surrounded by agricultural land (for example, up to 89% of the [[Maumee River]] drainage in Ohio). Lack of streamside buffers that separate agriculture and development projects from rivers can cause run-off and pollution.

Interstitial spaces in the [[substrate (aquatic environment)|substrate]] are an important part of the rayed bean's habitat because of their burrowing behavior. Large deposits of sedimentation and contaminants in sediment can degrade these spaces.<ref name=fwsdetermination />

===Pollution=== Chemical contaminants come from industrial and municipal discharge, spills, and agricultural and other run-off. Mussels have been shown to have high sensitivity to pollutants such as ammonia, metals, chlorine, and pesticides, and may affect them even in levels determined "safe" by [[United States Environmental Protection Agency|EPA]] standards. Nutrients such as [[nitrogen]] and [[phosphorus]] come from farm and livestock run-off can deplete dissolved oxygen levels.<ref name=fwsdetermination /> The Upper Thames River has some of the highest phosphorus levels in the region.<ref name=cosewic /> Pharmaceutical pollution from wastewater is an emerging but relatively unstudied threat and is common in the rayed bean's habitat.<ref name=fwsdetermination />

===Invasive species=== Dreissenid mussels ([[zebra mussel|zebra]] and [[quagga mussel|quagga]] mussels) are invasive freshwater mussels from eastern Europe that have become firmly established in parts of the rayed bean's range. Dreissenid mussels attach themselves to native mussels, reduce food particles in the water, interrupt reproduction, and foul the water with pseudofeces. Zebra mussels are established in the Great Lakes and Ohio River drainages, have eliminated rayed bean populations from [[Lake Erie]] and the [[Detroit River]], and have high potential to spread further.

Two introduced fish species, the [[round goby]] and the [[black carp]], are aggressive predators of mussels.

===Population fragmentation=== Many populations are geographically isolated and have become even more so as dams were constructed. Some are below the effective population size needed to sustain the population and maintain genetic diversity.<ref name=fwsdetermination />

===Localized threats=== Several localized threats have been identified for certain populations the rayed bean. These include contaminants from [[coal mining]] near the Elk River in West Virginia, gravel mining near the Allegheny and Tennessee watersheds, and oil and gas extraction from the [[Marcellus Shale|Marcellus]] and [[Utica Shale|Utica]] Shales.<ref name=fwsdetermination /> Dreissenid mussels from [[Fanshawe Lake]] in Ontario represent a potentially devastating threat to the Thames River population.<ref name=cosewic />

==Conservation efforts== It has been listed as Endangered in Canada on the [[List of Wildlife Species at Risk]] under the Canadian [[Species at Risk Act]] since 1999.<ref>COSEWIC. 2005. [http://www.sararegistry.gc.ca/virtual_sara/files/species/clwsa%5F0505%5Fe%2Epdf Canadian Species at Risk]. Committee on the Status of Endangered Wildlife in Canada. 64 pp., page 13.</ref> In 2012, it was listed as Endangered in the United States under the [[Endangered Species Act]], citing a reduction in range and declining, isolated populations.<ref name=fwsdetermination>Federal Register Vol 77, No. 30. Feb. 14, 2012: Determination of Endangered Status for the Rayed Bean and Snuffbox Mussels Throughout Their Ranges</ref> It holds protection at the state and provincial levels in several jurisdictions including Ontario, Michigan, Ohio, and Indiana.

The species' recent success has been mixed. Some new populations have been found since its Endangered listing in 2012, and the [[Allegheny River]] holds one of the largest current populations and appears to be increasing. A study found robust populations in locations in Ohio and New York in 2024.<ref name="j956">{{cite journal | last=Ford | first=David F. | last2=Grabarkiewicz | first2=Jeff | last3=Benshoff | first3=Adam | last4=Foltz | first4=David A. | last5=Kriege | first5=Mitchell | last6=Spaeth | first6=John | title=Population Demographic Data from Four Populations of the Federally Endangered Rayed Bean, ''Paetulunio (Villosa) fabalis'' (Mollusca: Unionidae) | journal=Freshwater Mollusk Biology and Conservation | volume=27 | issue=1 | date=2024-05-15 | issn=2472-2944 | doi=10.31931/fmbc-d-22-00008 | pages=1–7 | doi-access=free }}</ref>

However, Fish and Wildlife surveys have found it likely extirpated in other locations. Several recent bridges and infrastructure projects have been detrimental to this mussel,<ref name=5year2023 /> and a 2017 cleanup project for a decades-old petroleum spill near the city of [[Olean, New York]] affected thousands of rayed bean that had to be relocated from that area of the Allegheny.<ref name=5year2023>{{cite web|url=https://ecosphere-documents-production-public.s3.amazonaws.com/sams/public_docs/species_nonpublish/11001.pdf|title=Rayed Bean 5-Year Review 2023|author=USFWS|access-date=31 August 2024}}</ref><ref name=olean>{{cite news |url=https://www.oleantimesherald.com/news/exxonmobil-to-clean-up-allegheny-river-contamination-in-south-olean/article_3f939a25-0f54-5b6d-ac32-84f60e01d3ec.html|title=ExxonMobil to clean up Allegheny River contamination in South Olean|newspaper=Olean Times Herald |author=Bob Clark |date=2021-06-05 |access-date=2024-09-26|archive-date=2021-06-05|archive-url=https://web.archive.org/web/20210605183932/https://www.oleantimesherald.com/news/exxonmobil-to-clean-up-allegheny-river-contamination-in-south-olean/article_3f939a25-0f54-5b6d-ac32-84f60e01d3ec.html |url-status=live }}</ref>

[[File:Elk river in West Virginia.jpg|thumb|right|The Elk River in West Virginia]]

There have been several reintroduction efforts in different areas. The status of a 2006–07 translocation of mussels to the [[Elk River (West Virginia)|Elk River]] is uncertain, while a relocation to the [[Duck River (Tennessee)|Duck River]] in 2009 initially appeared successful. In 2020, over 5,000 rayed bean that had been salvaged from the Olean petroleum cleanup were transferred to the [[Green River (Kentucky)|Green River]] and [[Licking River (Kentucky)|Licking River]] in Kentucky, areas where the species had previously been extirpated.<ref name=5year2023 />

Since the life history of the rayed bean has been insufficiently studied, captive breeding is not yet possible.<ref name=5year2023 />

==References== {{Reflist}}

{{Taxonbar |from=Q107278717 |from2=Q107336417 |from3=Q3013948}}

[[Category:Unionidae]] [[Category:Monotypic bivalve genera]] [[Category:Freshwater animals of North America]] [[Category:Bivalves of North America]][[Category:Taxobox binomials not recognized by IUCN]] [[Category:ESA endangered species]] [[Category:IUCN Red List endangered species]]