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Rayed Bean and Snuffbox Mussels

Endangered and Threatened Wildlife and Plants; Listing the Rayed Bean and Snuffbox as Endangered


Below are the beginning sections of the Proposed Rule. Click here to download a 33-page PDF (240KB) file of the complete Federal Register Proposed Rule to List the Rayed Bean and Snuffbox as Endangered.



Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWSR3ES20100019]

[MO 9221000008B2]

RIN 1018–AV96


AGENCY:  Fish and Wildlife Service, Interior.


ACTION:  Proposed rule.


SUMMARY: We, the U.S. Fish and Wildlife Service (Service), propose to list the rayed bean (Villosa fabalis) and snuffbox (Epioblasma triquetra) as endangered throughout their ranges, under Endangered Species Act of 1973, as amended (Act).  This proposed rule, if made final, would extend the Act’s protection to the rayed bean and the snuffbox.  We have determined that designating critical habitat for these species is prudent, but not determinable at this time.  The Service seeks data and comments from the public on this proposed listing rule.


DATES:  We will consider comments we receive on or before January 3, 2010.  We must receive requests for public hearings, in writing, at the address shown in the FOR FURTHER INFORMATION CONTACT section on or before December 16, 2010.


ADDRESSES: You may submit comments by one of the following methods:

  • Federal eRulemaking Portal: http://www.regulations.gov.  Follow the instructions for submitting comments on Docket No. FWS-R3-2010-0019.
  • U.S. mail or hand-delivery:

    Public Comments Processing,
    Attn:  FWS-R3-2010-0019;
    Division of Policy and Directives Management;
    U.S. Fish and Wildlife Service;
    4401 N. Fairfax Drive, Suite 222;
    Arlington, VA 22203. 

We will post all comments on http://www.regulations.gov.  This generally means that we will post any personal information you provide us (see the Public Comments section below for more information).


FOR FURTHER INFORMATION CONTACT:  Angela Boyer at the U.S. Fish and Wildlife Service, Ohio Ecological Services Field Office, 4625 Morse Road, Suite 104, Columbus, OH 43230; telephone 614–416–8993, ext. 22.



Public Comments

Our intent is to use the best available commercial and scientific data as the foundation for all endangered and threatened species listing determinations.  We therefore request comments or suggestions from other concerned governmental agencies, the scientific community, industry, or any other interested party concerning this proposed rule to list the rayed bean and snuffbox as endangered. 


We particularly seek comments concerning:


(1) Survey results for the rayed bean or snuffbox, as well as any studies that may show distribution, status, population size, or population trends, including indications of recruitment;


(2)  Pertinent aspects of life history, ecology, and habitat use of the rayed bean or snuffbox;


(3) Current and foreseeable threats faced by the rayed bean or snuffbox, or both species, in relation to the five factors (as defined in section 4(a)(1) of the Act (16 U.S.C. 1531 et seq.));


(4) The specific physical and biological features to consider, and specific areas that may meet the definition of critical habitat and that should or should not be considered for a proposed critical habitat designation as provided by section 4 of the Act; and


(5) The data and studies to which this proposal refers.


You may submit your comments and materials concerning this proposed rule by one of the methods listed in the ADDRESSES section.  We will not accept comments sent by e-mail or fax or to an address not listed in the ADDRESSES section.  Comments must be submitted to http://www.regulations.gov before midnight (Eastern Time) on the date specified in the DATES section.  Finally, we will not consider hand-delivered comments that we do not receive, or mailed comments that are not postmarked, by the date specified in the DATES section.


We will post your entire comment —including your personal identifying information—on http://www.regulations.gov.  If you provide us personal identifying information such as your street address, phone number, or e-mail address, you may request at the top of your document that we withhold this information from public review.  However, we cannot guarantee that we will be able to do so.          


Comments and materials we receive, as well as supporting documentation we used in preparing this proposed rule, will be available for public inspection on http://www.regulations.gov, or by appointment, during normal business hours at the Ohio Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT).


Public Hearing

The Act provides for one or more public hearings on this proposal, if requested.  We must receive requests by the date listed in the DATES section above.  Such requests must be made in writing and addressed to the Field Supervisor of the Ohio Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT).



Species Descriptions

The rayed bean is a small mussel usually less than 1.5 inches (in) (3.8 centimeters (cm)) in length (Cummings and Mayer 1992, p. 142; Parmalee and Bogan 1998, p. 244; West et al. 2000, p. 248).  The shell outline is elongate or ovate in males and elliptical in females, and moderately inflated in both sexes, but more so in females (Parmalee and Bogan 1998, p. 244).  The valves are thick and solid.  The anterior end is rounded in females and bluntly pointed in males (Cummings and Mayer 1992, p. 142).  Females are generally smaller than males (Parmalee and Bogan 1998, p. 244).  Dorsally, the shell margin is straight, while the ventral margin is straight to slightly curved (Cummings and Mayer 1992, p. 142).  The beaks are slightly elevated above the hingeline (West et al. 2000, p. 248), with sculpture consisting of double loops with some nodules (Parmalee and Bogan 1998, p. 244).  No posterior ridge is evident.  Surface texture is smooth and sub-shiny, and green, yellowish-green, or brown in color, with numerous wavy, dark-green rays of various widths (sometimes obscure in older, blackened specimens) (Cummings and Mayer 1992, p. 142; West et al. 2000, p. 248).  Internally, the left valve has two pseudocardinal teeth (tooth-like structures along the hinge line of the internal portion of the shell) that are triangular, relatively heavy, and large, and two short, heavy lateral teeth (Cummings and Mayer 1992, p. 142).  The right valve has a low, triangular pseudocardinal tooth, with possibly smaller secondary teeth anteriorly and posteriorly, and a short, heavy, and somewhat elevated lateral tooth (Parmalee and Bogan 1998, p. 244).  The color of the nacre (mother-of-pearl) is silvery white or bluish and iridescent posteriorly.  Key characters useful for distinguishing the rayed bean from other mussels is its small size, thick valves, unusually heavy teeth for a small mussel, and color pattern (Cummings and Mayer 1992, p. 142).


The snuffbox is a small to medium-sized mussel with males reaching up to 2.8 in. (7.0 cm) in length (Cummings and Mayer 1992, p. 162; Parmalee and Bogan 1998, p. 108).  The maximum length of females is about 1.8 in (4.5 cm) (Parmalee and Bogan 1998, p. 108).  The shape of the shell is somewhat triangular (females), oblong, or ovate (males) with the valves solid, thick, and very inflated.  The beaks are located somewhat anterior of the middle, swollen, turned forward and inward, and extended above the hingeline (Cummings and Mayer 1992, p. 162).  Beak sculpture consists of three or four faint, double-looped bars (Cummings and Mayer 1992, p. 162; Parmalee and Bogan 1998, p. 108).  The anterior end of the shell is rounded, and the posterior end is truncated, highly so in females.  The posterior ridge is prominent, being high and rounded, while the posterior slope is widely flattened.  The posterior ridge and slope in females is covered with fine ridges and grooves, and the posterioventral shell edge is finely toothed (Cummings and Mayer 1992, p. 162).  When females are viewed from a dorsal or ventral perspective, the convergence of the two valves on the posterior slope is nearly straight due to being highly inflated.  This gives the female snuffbox a unique broadly lanceolate or cordate perspective when viewed at the substrate and water column interface (Ortmann 1919, p. 329; van der Schalie 1932, p. 104).  The ventral margin is slightly rounded in males and nearly straight in females.  Females have recurved denticles on the posterior shell margin that aid in holding host fish (Barnhart 2008, p. 1).  The periostracum (external shell surface) is generally smooth and yellowish or yellowish-green in young individuals, becoming darker with age.  Green squarish, triangular, or chevron-shaped marks cover the umbone (the inflated area of the shell along the dorsal margin) but become poorly delineated stripes with age.  Internally, the left valve has two high, thin, triangular, emarginate pseudocardinal teeth (the front tooth being thinner than the back tooth) and two short, strong, slightly curved, and finely striated lateral teeth.  The right valve has a high, triangular pseudocardinal tooth with a single short, erect, and heavy lateral tooth.  The interdentum (a flattened area between the pseudocardinal and lateral teeth) is absent, and the beak cavity is wide and deep.  The color of the nacre is white, often with a silvery luster, and a gray-blue or gray-green tinge in the beak cavity.  The soft anatomy was described by Oesch (1984, pp. 233–234), and Williams et al. (2008, p. 282).  Key characters useful for distinguishing the snuffbox from other species include its unique color pattern, shape (especially in females), and high degree of inflation. 



The rayed bean is a member of the freshwater mussel family Unionidae and was originally described as Unio fabalis by Lea in 1831.  The type locality is the Ohio River (Parmalee and Bogan 1998, p. 244), probably in the vicinity of Cincinnati, Ohio.  Over the years, the rayed bean has been placed in the genera Unio, Margarita, Margaron, Eurynia, Micromya, and Lemiox.  It was ultimately placed in the genus Villosa by Stein (1963, p. 19), where it remains today (Turgeon et al. 1998, p. 33).  We recognize Unio capillus, U. lapillus, and U. donacopsis as synonyms of Villosa fabalis.


The snuffbox is a member of the freshwater mussel family Unionidae and was described as Truncilla triqueter (Rafinesque 1820, p. 300).  The species name was later changed to triquetra (Simpson 1900, p. 517), from the Latin triquetrous meaning “having three acute angles,” a reference to the general shape of the female.  The type locality is the Falls of the Ohio (Ohio River, Louisville, Kentucky) (Parmalee and Bogan 1998, p. 108). The synonymy of the snuffbox was summarized by Johnson (1978, pp. 248–249), Parmalee and Bogan (1998, p. 108), and Roe (no date, p. 3).  This species has also been considered a member of the genera Unio, Dysnomia, Plagiola, Mya, Margarita, Margaron, and Epioblasma at various times since its description.  The monotypic subgenus Truncillopsis was created for this species (Ortmann and Walker 1922, p. 65).  The genus Epioblasma was not in common usage until the 1970s (Stansbery 1973, p. 22; Stansbery 1976, p. 48; contra Johnson 1978, p. 248), where it currently remains (Turgeon et al. 1998, p. 34).  Unio triqueter, U. triangularis, U. triangularis longisculus, U. triangularis pergibosus, U. cuneatus, and U. formosus are recognized as synonyms of E. triquetra.  Tricorn pearly mussel is another common name for this species (Clarke 1981a, p. 354).


Life History

The general biology of the rayed bean and the snuffbox are similar to other bivalved mollusks belonging to the family Unionidae.  Adults are suspension-feeders, spending their entire lives partially or completely buried within the substrate (Murray and Leonard 1962, p. 27).  Adults feed on algae, bacteria, detritus, microscopic animals, and dissolved organic material (Silverman et al. 1997, p. 1859; Nichols and Garling 2000, p. 873; Christian et al. 2004, pp. 108–109; Strayer et al. 2004, pp. 430–431).  Recent evidence suggests that adult mussels may also deposit-feed on particles in the sediment (Raikow and Hamilton 2001, p. 520).  For their first several months, juvenile mussels employ foot (pedal) feeding, consuming settled algae and detritus (Yeager et al. 1994, p. 221).  Unionids have an unusual mode of reproduction.  Their life cycle includes a brief, obligatory parasitic stage on fish.  Eggs develop into microscopic larvae called glochidia within special gill chambers of the female.  The female expels the mature glochidia, which must attach to the gills or the fins of an appropriate fish host to complete development.  Host fish specificity varies among unionids.  Some species appear to use a single host, while others can transform on several host species.  Following successful infestation, glochidia encyst (enclose in a cyst-like structure) and drop off as newly transformed juveniles.  For further information on freshwater mussels, see Gordon and Layzer (1989, pp. 1–17).


Mussel biologists know relatively little about the specific life-history requirements of the rayed bean and the snuffbox.  Most mussels, including the rayed bean and snuffbox, have separate sexes.  The age at sexual maturity, which is unknown for the rayed bean and snuffbox, is highly variable among and within species (0–9 years) (Haag and Staton 2003, pp. 2122–2123), and may be sex dependent (Smith 1979, p. 382).  Both species are thought to be long-term brooders; rayed bean females brood glochidia from May through October (Parmalee and Bogan 1998, p. 108; Ecological Specialists, Inc. (ESI) 2000, p. 5; Woolnough 2002, p. 23), and snuffbox brood glochidia from September to May (Ortmann 1912, p. 355; 1919, p. 327).  The only published research identifies the Tippecanoe darter (Etheostoma tippecanoe) as a host fish for the rayed bean (White et al. 1996, p. 191).  Other rayed bean hosts are thought to include the greenside darter (E. blennioides), rainbow darter (E. caeruleum), mottled sculpin (Cottus bairdi), and largemouth bass (Micropterus salmoides) (Woolnough 2002, p. 51).  Based on inference of closely related species, additional hosts may be suitable, including other darter and sculpin species (Jones 2002, pers. comm.).  Juvenile snuffbox have successfully transformed on logperch (Percina caprodes), blackside darter (P. maculata), rainbow darter, Iowa darter (E. exile), blackspotted topminnow (Fundulus olivaceous), mottled sculpin, banded sculpin (C. carolinae), Ozark sculpin (C. hypselurus), largemouth bass, and brook stickleback (Culaea inconstans) in laboratory tests (Sherman 1994, p. 17; Yeager and Saylor 1995, p. 3; Hillegass and Hove 1997, p. 25;  Barnhart et al. 1998, p. 34; Hove et al. 2000, p. 30; Sherman Mulcrone 2004, pp. 100–103). 


Habitat Characteristics

The rayed bean is generally known from smaller, headwater creeks, but occurrence records exist from larger rivers (Cummings and Mayer 1992, p. 142; Parmalee and Bogan 1998, pp. 244).  They are usually found in or near shoal or riffle areas, and in the shallow, wave-washed areas of glacial lakes, including Lake Erie (West et al. 2000, p. 253).  In Lake Erie, the species is generally associated with islands in the western portion of the lake.  Preferred substrates typically include gravel and sand.  The rayed bean is oftentimes found among vegetation (water willow (Justicia americana) and water milfoil (Myriophyllum sp.)) in and adjacent to riffles and shoals (Watters 1988b, p. 15; West et al. 2000, p. 253).  Specimens are typically buried among the roots of the vegetation (Parmalee and Bogan 1998, pp. 245).  Adults and juveniles appear to produce byssal threads (thin, protein-based fibers) (Woolnough 2002, pp. 99–100), apparently to attach themselves to substrate particles.


The snuffbox is found in small to medium-sized creeks to larger rivers and in lakes (Cummings and Mayer 1992, p. 162; Parmalee and Bogan 1998, p. 108).  The species occurs in swift currents of riffles and shoals and wave-washed shores of lakes over gravel and sand with occasional cobble and boulders.  Individuals generally burrow deep into the substrate except when spawning or attempting to attract a host (Parmalee and Bogan 1998, p. 108). 


Strayer (1999a, pp. 471–472) 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.  He thought that features commonly used in the past to explain the spatial patchiness of mussels (water depth, current speed, sediment grain size) were poor predictors of where mussels actually occur in streams. 


Above are the beginning sections of the Proposed Rule. Click here to download a 33-page PDF (240KB) file of the complete Federal Register Proposed Rule to List the Rayed Bean and Snuffbox as Endangered.


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Last updated: September 21, 2016