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Freshwater Bivalves of North America
Caleb Royon 27 October 2012
Transcript of Freshwater Bivalves of North America
Unionoida The mussels of this group have very minimal hinge teeth as adults or none at all. The glochidia possess a pair of hooks that enable them to clamp onto external features of host fish such as fins and scales. All members of this group have very thick shells with well-developed hinge teeth. The glochidia all lack hooks and therefore encyst on the gills of the host fish. Several species produce conglutinates (worm-like lures) that are released into the water column. These often mimic food items fish prefer. For this reason most have a large array of suitable fish hosts. The mussels within this subfamily often have shells that are sexually dimorphic (males and females are visibly different). Female shells are typically inflated. This provides more room for the females to brood her many young within her gill pouches. The glochidia from this group are all gill parasites. The females often have a developed visual lure as part of their mantle tissue that is inflated, extended and moved independently. This mantle tissue often realistically mimics a small baitfish or crayfish. Water clarity is essential for the host fishes to see the lures being displayed by these gravid females. family ELKTOE Alasmidonta Marginata - 5in The elktoe is a beautifully marked, relatively thin-shelled mussel with narrow rays and spots on a background of bright, yellowish-green. It typically lives in swift, flowing riffles with stable gravel or gravel-sand substrates. Freshwater mussels have an extendible foot used for locomotion. In the elktoe, it is orange and elongated. Although rare, this mussel is found in the Spring and Marais des Cygnes rivers. FLAT FLOATER Anodonta Suborbiculata - 8in Relative to other mussels, the flat floater is a short-lived species (8-12 years). Its thin, yellowish-green shell is smooth, shiny and nearly circular. There are no interlocking teeth to help hold its two valves together. This mussel prefers the soft mud of oxbow lakes and ponds occasionally flooded by the Neosho and Marais des Cygnes rivers. In late winter a female releases mucous strands laced with glochidia. When a fish swims through this “web,” some of the glochidia clamp down on the fish’s fins. If the fish is a suitable host and a spring flood occurs, the fish will carry these “hitchhikers” to invade other oxbow habitats where they drop off and grow. CYLINDRICAL PAPERSHELL Anodontoides Ferrusacianus - 3.5in This mussel has a straw-colored, thin shell with a smooth and shiny exterior. Young shells reveal fine V-ridges on the umbo. The nacre is white. While most of the mussels in Kansas are found in the southeastern part of the state, the cylindrical papershell’s range was across the northern half of Kansas. Relic shells have been found in the Kansas, Saline, Nemaha and Blue rivers. Currently, the only remaining population exists in a short stretch of the Smoky Hill River. Low to nonexistent stream flow rates threaten the remaining population in Kansas. WHITE HEELSPLITTER Lasmigona Complanata - 8in The white heelsplitter is a large flattened mussel shaped similar to a dinner plate with a flat, narrow-edged wing extending from the dorsal margin. As its name implies, this wing is so narrow-edged it could split your heel if you stepped on it with a bare foot. It has notable fine ridges on the umbo that resemble the number 3. Internally, this shell is entirely white with undeveloped lateral teeth that fail to interlock. This mussel is often found in the pools or slow runs of rivers, small perennial creeks and even reservoirs. FLOATER Pyganodon Grandis - 10in The floater’s shell varies from tan to dark greenish-brown then to dark brown in the older shells. It has no interlocking teeth. The large umbos are centered on the shell and give the floater an inflated appearance. This mussel largely inhabits calm water of mud, silt or sand substrate, therefore, it is usually found in ponds, oxbows, reservoirs and slow pools of streams. Unlike most freshwater mussels that may live decades, the floater lives only about 10 years. It gets its name from the supposed ability to float in the water to move to a new location if conditions deteriorate. These mussels have been seen floating but they were already dead. Evidently, the trapped gases of decomposition cause this mussel to float. CREEPER Strophitus Undulatus - 4.5in The creeper has a thin, oval-shaped shell that causes the mussel to feel light for its size. Young shells are frequently yellow, rayed with green, turning dark brown to black with age. Internally, the nacre is also variable in color from cream to white, bluish-white or even salmon-colored. The lateral teeth are reduced and do not interlock. The creeper resides in most southeast Kansas streams with permanent flow. Some research suggests this species’ glochidia do not require a fish host, but they will attach to a fish if given the opportunity. PAPER PONDSHELL Utterbackia Imbecillus - 3.75in
This species inhabits still waters, thus is largely found in isolated ponds, oxbows, backwaters and permanent pools. It is well adapted to mud substrates. Its shells are usually found along shores where raccoons, muskrats and birds have used them for food. As the name implies, the paper pondshell has a paper-thin shell and can be found in ponds. The shell is yellow to greenish-yellow and often cracks upon drying so is easily broken. Internally, there are no interlocking teeth and the nacre is whitish-blue and iridescent.
The BUTTERFLY Ellipsaria Lineolata - 6in The butterfly has a dazzling, golden-yellow shell with dark, broken, radiating rays. The overall shape, when viewed at a distance, resembles its namesake. The shells are dimorphic as the male’s shape is flatter than the female. The shell was once valuable in the button industry. Butterfly mussels reportedly are disappearing from many areas where they formerly were found. A few still inhabit the best mussel sites of the Fall, Verdigris, Neosho and Marais des Cygnes rivers. The fish hosts for the butterfly represent three different families of native fish. POCKETBOOK Lampsilis Cardium - 7in The plain pocketbook is relatively easy to identify because of its large umbos. However, male and female mussels of this species are dimorphic, meaning their shapes differ. The female is more inflated as she requires more internal space to brood her eggs within gill pouches each year. The male is longer and more pointed at its posterior end than the female. See pages 10-11 for a detailed account of plain pocketbook reproduction. The plain pocketbook is widespread but is never found in high numbers at any site. One intact shell was found in a Pleistocene bank deposit where mammoth and ground sloth bones were also buried. FATMUCKET Lampsilis Siliquoidea - 6.5in The fatmucket is sexually dimorphic in shape. With age, females develop into a hatchet shape, the anterior end being much smaller than the posterior end. This difference is to provide more room to brood the eggs in her gills while the male’s shape with age is more symmetrical. Like other Lampsilis mussels, the female displays a large lure to attract host fish. This lure is less fish-like than others within the Lampsilis group yet still attractive to a variety of host fish. The fatmucket is more likely found in smaller streams and can be found in some reservoirs. YELLOW SANDSHELL Lampsilis Teres - 5.5in The yellow sandshell is a long and rather narrow mussel. Because of its color and shape some of the old shellers would refer to it as the “banana boat,” while another colloquial name is “bank creeper” because it tends to crawl around. It is sexually dimorphic, with the female being slightly more bulged in appearance than the male.
The female has a mantle lure to entice fish into close range to
enhance the probability of glochidia encystment on the host
fish. This mussel is widespread in Kansas but never reaches
high densities in any location. It is better represented in
southeast Kansas and is sometimes found in sparse
numbers in reservoirs. Historically, the yellow sandshell
was found farther north and west in Kansas streams
where relic shells can be found as evidence of
past occurrence. THREEHORN-WARTYBACK Obliquaria Reflexa - 3.25in The threehorn wartyback typically has three large protruding pustules on its shell which led to its common name. However, sometimes two or four of these pustules are found on each valve. These pustules are arranged alternately from the ones on the opposite valve. The similar-appearing wartyback (Q. nodulata) has pustules arranged opposite the ones on the opposing valve. The threehorn wartyback is a river species, and it ranks near the top in overall density at several sample sites. It is seldom found in small streams. The female releases glochidia in the late spring to early summer. There is some speculation this mussel does not always require a fish host to metamorphose from the larval to the juvenile stage. More research is needed to clarify the life history of this shell. PINK HEELSPLITTER Potamilus Alatus - 8in The pink heelsplitter gets its name from the large, flat wing often found extending from the dorsal side of the shell. This “wing” has a very narrow edge and if stepped on, might easily injure a person’s bare foot. The shell’s interior has a showy, purplish-pink nacre that may be tinged with a bronze color. Young shells have green rays that fade with age. The glochidia within this genus Potamilus are uniquely hatchet-shaped. Other mussels have round-shaped glochidia. Research has shown this species can be utilized in the culture of purple pearls. Other colloquial names for the pink heelsplitter are “hatchetback” and “pancake.” In Kansas, the pink heelsplitter is restricted to the Kansas and Marais des Cygnes river basins. In these flowing waters, it is more commonly found in pools and sluggish areas where it can be found in a mix of gravel and silt substrates. BLEUFER Potamilus Purpuratus - 7in The bleufer is best known for its brilliant purple nacre which gives it the scientific name purpuratus. It is sometimes called “purple shell.” Externally, the bleufer has a very dark periostracum and a slight wing arising on its dorsal side. It is one of the larger mussels in Kansas. The female is more inflated and truncated toward the posterior end. Because of its colored nacre and large size, it has been used in the past for jewelry inlays. It is most confused with the pink heelsplitter. In similar sized shells, the bleufer has a more inflated, heavier shell and the ventral margin is nearly straight. The bleufer appears to be a habitat generalist and can be found in pools, riffles and runs of rivers and is often present in reservoirs and below low-head dams. This is a southern Mississippi River Basin species and is at the northwest periphery of its range in southeast Kansas. FAWNSFOOT Truncilla Donaciformis - 2.25in The fawnsfoot is one of the smallest mussels in Kansas rivers. The markings on the shell are striking because they look like zigzags, scribbles or wide, dark rays on a background of golden to light brown. Fawnsfoot mussels can sometimes be found washed up along the shoreline of reservoirs.
The juvenile fawnsfoot produces a byssal thread it attaches to a small rock or even a nearby larger mussel shell. These act as anchors to keep this small mussel from being washed downstream. The only known host fish in Kansas is the freshwater drum, a fish well known for its appetite for small mussels. The fawnsfoot is found in the rivers of eastern Kansas. PINK PAPERSHELL Potamilus Ohiensis - 6in Externally, the pink papershell is flattened with a dorsal wing that becomes jagged with age. The shell color is chestnut brown and has a shiny luster. As the name implies, the shell is very thin with dark pink or purple nacre from margin to margin.
The shell from a dead specimen may crack as it dries. It is often confused with the fragile papershell, but differs in having a more rounded ventral surface and a darker shell color. The pink papershell is most common in still water but can occur in low numbers in rivers. It can be found in central Kansas within several sandy streams and the Arkansas River. Because it is adapted to live in ox-bow environments, it sometimes reaches high numbers in some reservoirs. It apparently does well in silty substrates that many other species cannot tolerate. It has been used in studies to detect the toxic effects of ammonia. Deertoe Truncilla Truncata - 3in This is a very well-marked mussel with a shell showing numerous greenish rays, chevrons or zigzag patterns on a background of yellowish, greenish or reddish-brown. The nacre is white or various shades of pink. It is closely related to the fawnsfoot, but is larger with a more sharply angled posterior margin.
It is generally more triangular-shaped which reflects its common name, the deertoe. It can be found in several southeast Kansas rivers and streams. It appears to be rare below some reservoirs, suggesting fish are unable to transport the juveniles to these locations because the dams act as barriers to dispersal. THREERIDGE Ablema Plicata - 7in This thick-shelled mussel gets its name from the three prominent ridges (sometimes two or four) that are easily noticed. On older specimens, the periostracum (external layer) is worn off the umbos and they appear white. Shellers called them “old gray beards.” In some Kansas rivers, the threeridge is the most common mussel. This species does well in rivers and streams and can tolerate more pollution than other native mussels. Its glochidia are released from late spring to early summer. Threeridge shells were extensively utilized in the pearl button and cultured pearl industries due to their thickness and unblemished nacre. PURPLE WARTYBACK Cycolonaias Tuberculata - 6in As the name implies, the purple wartyback has pustules (bumps) on the exterior of its dark brown shell. Internally, the nacre is a coppery-purple color. Because of this colored interior, it was never valued for the button industry. Its shell appears more rounded as compared to other thick-shelled species.
Within Kansas, its distribution and abundance is limited to the lower reaches of the Marais des Cygnes River. However, further downstream in Missouri it was noted as the most abundant shell of the mussel community. It is widespread across the eastern United States but is seldom common at any location. In some of the Great Lakes drainages, the purple wartyback has returned to rivers where water quality has improved. SPIKE Elliptio Dilatata - 5.5in The spike is an elongated, heavy, smooth-shelled mussel. The older shells are dark brown and the bottom margin is slightly arched. It could be mistaken for the kidneyshell or spectaclecase mussels. The nacre may be dark purple, lilac, pink, salmon, bluish-white, white or a combination of these colors.
It is normally found partially buried within swift currents of gravel or cobble substrate. The spike is known for the occasional black pearl it produces. Another name sometimes used for the spike is ladyfinger. It is found in the Spring, Neosho and Marais des Cygnes rivers but was once more widespread. WABASH PIGTOE Fusconaia Flava - 4.5in The Wabash pigtoe has no external bumps, waves or rays to help identify it. Its shape can vary from being nearly round to very elongate. The external color is reddish or yellowish-brown, becoming darker with age. Darker growth-rest lines (rings) are often obvious. Inside, the nacre is white, salmon or rose pink. It is often mistaken for the round pigtoe. The orange foot color is a helpful identifying characteristic, contrasting with the tan to whitish foot of the round pigtoe.
The Wabash pigtoe is found in rivers and large creeks of eastern Kansas. Its past distribution was farther north and west where relic shells can still be located in the Ninnescah, Chikaskia, Republican and South Fork Big Nemaha rivers. A closely related mussel, the Ozark pigtoe, is very similar to the Wabash pigtoe but is smaller, more flattened and of uniform shell thickness. It may occur in the Spring River of Cherokee County. MONKEYFACE Quadrula Metanevra - 4.5in The monkeyface has a very prominent posterior ridge and is sometimes strikingly marked with dark triangles. By viewing the shell edge-on and using your imagination you can see the face of a monkey. It is a river species and is most common in riffles and swift runs.
Because of its heavy shell, white nacre and decent numbers, it was also targeted in the button and cultured pearl industry. Its population density has apparently been increasing at some sampling sites in southeast Kansas. This is a positive sign for all native mussels. However, it is absent above some of the large mainstem reservoirs in southeastern Kansas. RABBITSFOOT Quadrula Cylindrica - 5in The rabbitsfoot is named for its general shape. Its length is about three times longer than its height. The elongate, greenish-brown shell has a row of knobs and often exhibits a beautiful pattern of dark triangles. It is one of the rarest mussels in Kansas.
It is found in clear streams with swift current flowing over stable gravel substrates. Specimens can be found in the Spring River and a short stretch of the mid-Neosho River. The Verdigris River currently contains chalky, long dead specimens only. However, surveys in Oklahoma recently discovered an extant population below Oologah Reservoir. So, propagating and reintroducing juveniles to sites upriver in Kansas remains a possibility to help recover this species. ROUND PIGTOE Pleurobema Sintoxia - 4.5in This mussel is most easily confused with the Wabash pigtoe, although the round pigtoe is typically darker, less flattened and has a higher umbo than the Wabash pigtoe. Also, the younger round pigtoe has noticeable dark greenish rays that radiate from the umbo region.
If identification is still in question, the pigtoe can be slightly pried open to examine the internal tissue coloration. The foot of the round pigtoe is light tan-gray to white while the Wabash pigtoe has an orange cast. The nacre in the round pigtoe is usually white, but pink, rose and salmon colors can be found in limited numbers and make the shell interior very striking. The round pigtoe appears to be declining across its range. In Kansas, however, its population may be increasing in the Verdigris River. WASHBOARD Megalonaias Nervosa - 11in The washboard is the largest and probably the longest-lived freshwater mussel in North America. The shell exterior is nearly black and roughened (like a washboard) with ridges and grooves. Young washboards have a noticeable zigzag sculpturing in the umbo area that over time erodes to a smooth surface. It could be confused with large threeridge shells.
Using growth-rest lines (rings) as reference, some authorities believe these mollusks can live over a century. Also, these mussels have been located in several archeological sites suggesting Indians used these large shells for plates, hoes or scrapers. The females release glochidia in late winter.
There are several potential fish hosts for this species in Kansas rivers. The washboard can be found in the Marais des Cygnes, Fall, Verdigris and Neosho rivers and the lower end of Labette Creek. PONDHORN MUSSEL Uniomerus Tetralasmus - 4.5in As the name implies, the pondhorn is typically found in ponds, small lakes or the pooled headwaters of small streams. It has the unusual capability of going dormant in dry conditions by burying itself deeply in the mud. It can survive exposure to air for up to 578 days at 59° F. To conserve water, it will plug its siphons with mucous. After sufficient rainfall, it will resume life processes by siphoning water over its gills.
This mussel has a unique distinguishing characteristic: two shallow parallel grooves extending from the umbo area outward to the posterior margin. The color of the periostracum sometimes abruptly changes from yellow to dark brown at a growth-rest line (ring).
The shell is relatively smooth but may have a slight ridge where these rest lines are located. Because of its relatively thin shell, the pondhorn is often eaten by muskrats. It is widespread and is one of the few species that can be found in southwest Kansas. PISTOLGRIP Tritogonia Verrucosa - 7in With the general shape of a pistolgrip, this mussel is easily identified. The sexes differ in shape as the female is more elongated than the male. Recent research has also shown pistolgrips will move toward each other as spawning season approaches. This may help ensure the eggs within the female’s gill pouches are fertilized because the male simply releases sperm into the open water.
Its fish hosts are all in the catfish family and some authorities believe it uses scent to attract these host fish to enhance its chances of completing its life cycle. The pistolgrip is found in rivers and streams with permanent flow and occasionally in reservoirs. PIMPLEBACK Quadrula Pustulosa - 4in The pimpleback usually has pustules on its shell but sometimes it can be found without this characteristic and the shell is smooth. The overall appearance is circular with the exception of a squared-off posterior margin. It is a common mussel where found and is typically in the top three mussel species in abundance at river sample sites in southeast Kansas. WARTYBACK Quadrula Nodulata - 4.5in The wartyback is a straw-colored mussel that looks very similar to its closest relative, the pimpleback, but differs by having fewer and larger pustules on the shell. These knob-like structures are most notably arranged in diverging rows exactly opposite the knobs on the opposing valve. These features are an adaptation to help this mussel stay anchored in the substrate, especially during flood conditions.
In addition to the pimpleback, the wartyback can also be confused with the threehorn wartyback. Another characteristic to help differentiate this shell is a pronounced wing on the posterior portion of the shell. The wartyback is found in most southeast Kansas rivers but is not numerous. Within some of the best Verdigris River mussel beds, one wartyback will be found for every 100 mussels identified. MAPLELEAF Quadrula Quadrula - 5in The mapleleaf shell’s shape resembles its namesake. A noticeable ridge, with an adjacent valley (finger groove), is consistently apparent in the external shell structure. This groove, or sulcus, is often bordered by a row of pustules lining each ridge.
This mussel species has the most shell variability across its wide geographical range in North America, creating taxonomic struggles. It is unique in having the flathead catfish as its only known fish host. Without this fish present, the mapleleaf would eventually disappear. Because host fish can gain immunity from past glochidia infestations, it is necessary that young flathead catfish be produced each year to be suitable candidates to host mapleleaf glochidia.
The mapleleaf is found in a wide array of habitats including small sandy streams in western Kansas, backwater pools within larger rivers and even large reservoirs. This suggests it is a generalist species and more tolerant of pollution than other mussels.
The Great Plains Nature Center
TTC Shells Ltd.
TIK & TOC with special thanks to
KANSAS UNIONIDS VISUALIZED
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