Scale shell
Encyclopedia
The scale shell or scaleshell (Leptodea leptodon) is a species
of freshwater mussel in the family Unionidae
, the river mussels. This aquatic
bivalve mollusk has disappeared from much of its historical range. It is endemic to the United States
, where it is now present in four or fewer states; it is only found with any regularity in Missouri
. It is a federally listed endangered species
of the United States.
This mussel is generally up to 10 centimeters long but old individuals may reach 12 centimeters. The shell is very thin and translucent in parts, and is yellowish, greenish, or brownish in color. The nacre
is very iridescent and is blue or purple in color with a pinkish or copper tinge. The species is sexually dimorphic
, with males having a pointed posterior end and females having a ruffled end.
This mussel had a historical distribution in 56 rivers in 13 states throughout the Mississippi River
drainage: Alabama
, Arkansas
, Illinois
, Indiana
, Iowa
, Kentucky
, Minnesota
, Missouri
, Ohio
, Oklahoma
, South Dakota
, Tennessee
, and Wisconsin
. While it had a widespread distribution, it was considered rare throughout its range. Today it is considered extirpated
from nine of these states, with scattered occurrences remaining in Missouri, South Dakota, Arkansas, and Oklahoma. It has been seen in 18 rivers in the last 25 years. The largest known populations, which are very small and isolated, are in the Meramec, Bourbeuse
, and Gasconade River
s of Missouri.
Most freshwater mussels reproduce by releasing their larvae, called glochidia
, into the water, where they are then taken in by fish. The glochidia lodge in the gills or fins of the fish and develop into juvenile mussels encysted in the fish tissue. They then drop off the fish into the substrate. Little is known about how this species transfers its glochidia to fish hosts, but it may occur when the adult female is eaten by the fish. The fish host for this mussel species is the freshwater drum
(Aplodinotus grunniens).
This mussel inhabits medium-sized to large rivers and can be found in riffle
s with a slow or moderate current
. It often buries itself a few centimeters deep in the substrate, which may be sand, gravel, rocks, or mud. It can be found among other species of mussels in the few remaining fragments of appropriate habitat.
The main threat to this species is the loss and degradation of its habitat. Channelization and impoundment
of the river systems have eliminated large areas of habitat. Increased sedimentation
and pollution
have degraded remaining areas. The best populations on the Meramec River are threatened by pollution from lead mining
. Sand mining
and dredging kill individuals. Riverbank erosion
removes strips of habitat and may increase sedimentation and pollution.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of freshwater mussel in the family Unionidae
Unionidae
Unionidae is a family of freshwater mussels, the largest in the order Unionoida, the bivalve mollusks sometimes known as river mussels, naiads, or simply as unionids.The range of distribution for this family is world-wide...
, the river mussels. This aquatic
Aquatic animal
An aquatic animal is an animal, either vertebrate or invertebrate, which lives in water for most or all of its life. It may breathe air or extract its oxygen from that dissolved in water through specialised organs called gills, or directly through its skin. Natural environments and the animals that...
bivalve mollusk has disappeared from much of its historical range. It is endemic to the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, where it is now present in four or fewer states; it is only found with any regularity in Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
. It is a federally listed endangered species
Endangered species
An endangered species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters...
of the United States.
This mussel is generally up to 10 centimeters long but old individuals may reach 12 centimeters. The shell is very thin and translucent in parts, and is yellowish, greenish, or brownish in color. The nacre
Nacre
Nacre , also known as mother of pearl, is an organic-inorganic composite material produced by some mollusks as an inner shell layer; it is also what makes up pearls. It is very strong, resilient, and iridescent....
is very iridescent and is blue or purple in color with a pinkish or copper tinge. The species is sexually dimorphic
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
, with males having a pointed posterior end and females having a ruffled end.
This mussel had a historical distribution in 56 rivers in 13 states throughout the Mississippi River
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
drainage: Alabama
Alabama
Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...
, Arkansas
Arkansas
Arkansas is a state located in the southern region of the United States. Its name is an Algonquian name of the Quapaw Indians. Arkansas shares borders with six states , and its eastern border is largely defined by the Mississippi River...
, Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
, Indiana
Indiana
Indiana is a US state, admitted to the United States as the 19th on December 11, 1816. It is located in the Midwestern United States and Great Lakes Region. With 6,483,802 residents, the state is ranked 15th in population and 16th in population density. Indiana is ranked 38th in land area and is...
, Iowa
Iowa
Iowa is a state located in the Midwestern United States, an area often referred to as the "American Heartland". It derives its name from the Ioway people, one of the many American Indian tribes that occupied the state at the time of European exploration. Iowa was a part of the French colony of New...
, Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...
, Minnesota
Minnesota
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
, Missouri
Missouri
Missouri is a US state located in the Midwestern United States, bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska. With a 2010 population of 5,988,927, Missouri is the 18th most populous state in the nation and the fifth most populous in the Midwest. It...
, Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
, Oklahoma
Oklahoma
Oklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
, South Dakota
South Dakota
South Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, Tennessee
Tennessee
Tennessee is a U.S. state located in the Southeastern United States. It has a population of 6,346,105, making it the nation's 17th-largest state by population, and covers , making it the 36th-largest by total land area...
, and Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
. While it had a widespread distribution, it was considered rare throughout its range. Today it is considered extirpated
Local extinction
Local extinction, also known as extirpation, is the condition of a species which ceases to exist in the chosen geographic area of study, though it still exists elsewhere...
from nine of these states, with scattered occurrences remaining in Missouri, South Dakota, Arkansas, and Oklahoma. It has been seen in 18 rivers in the last 25 years. The largest known populations, which are very small and isolated, are in the Meramec, Bourbeuse
Bourbeuse River
The Bourbeuse River is a river located in east-central Missouri, in the Ozarks region, and is one of two major tributaries of the Meramec River, the other being the Big River...
, and Gasconade River
Gasconade River
The Gasconade River is about long and is located in central and south-central Missouri in the United States.The Gasconade River begins in the Ozarks southeast of Hartville in Wright County and flows generally north-northeastwardly through Wright, Laclede, Pulaski, Phelps, Maries, Osage and...
s of Missouri.
Most freshwater mussels reproduce by releasing their larvae, called glochidia
Glochidium
The glochidium is a special microscopic larval stage of larger freshwater mussels, aquatic bivalve mollusks in the families Unionidae and Margaritiferidae, the river mussels and European freshwater pearl mussels....
, into the water, where they are then taken in by fish. The glochidia lodge in the gills or fins of the fish and develop into juvenile mussels encysted in the fish tissue. They then drop off the fish into the substrate. Little is known about how this species transfers its glochidia to fish hosts, but it may occur when the adult female is eaten by the fish. The fish host for this mussel species is the freshwater drum
Freshwater Drum
-Introduction:The freshwater drum, Aplodinotus grunniens, is a fish endemic to North and Central America. It is the only species in the genus Aplodinotus. The Freshwater drum is a member of the family Sciaenidae, and is the only member of the species that inhabits freshwater for its entire life...
(Aplodinotus grunniens).
This mussel inhabits medium-sized to large rivers and can be found in riffle
Riffle
A Riffle is a short, relatively shallow and coarse-bedded length of stream over which the stream flows at higher velocity and higher turbulence than it normally does in comparison to a pool....
s with a slow or moderate current
Current (stream)
A current, in a river or stream, is the flow of water influenced by gravity as the water moves downhill to reduce its potential energy. The current varies spatially as well as temporally within the stream, dependent upon the flow volume of water, stream gradient, and channel geometrics...
. It often buries itself a few centimeters deep in the substrate, which may be sand, gravel, rocks, or mud. It can be found among other species of mussels in the few remaining fragments of appropriate habitat.
The main threat to this species is the loss and degradation of its habitat. Channelization and impoundment
Dam
A dam is a barrier that impounds water or underground streams. Dams generally serve the primary purpose of retaining water, while other structures such as floodgates or levees are used to manage or prevent water flow into specific land regions. Hydropower and pumped-storage hydroelectricity are...
of the river systems have eliminated large areas of habitat. Increased sedimentation
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
and pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
have degraded remaining areas. The best populations on the Meramec River are threatened by pollution from lead mining
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
. Sand mining
Sand mining
Sand mining is a practice that is becoming an environmental issue as the demand for sand increases in industry and construction. Sand is mined from beaches and inland dunes and dredged from ocean beds and river beds. It is often used in manufacturing as an abrasive, for example, and it is used to...
and dredging kill individuals. Riverbank erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
removes strips of habitat and may increase sedimentation and pollution.
Source
- Bogan, A.E. 1996. Leptodea leptodon. 2011 IUCN Red List of Threatened Species. Downloaded on 25 September 2011.