Megalonaias nervosa

Geographic Range

Megalonaias nervosa, a freshwater mussel called the washboard, can be found in 18 states around the United States. The washboard's horizontal geographic boundary starts in South Dakota and moves east until reaching Ohio. The vertical geographic boundary for the washboard starts in Minnesota and stretches south to the Gulf of Mexico, including Texas and the very northeastern tip of Mexico. ("Megalonaias nervosa", 2011; Clayton, 2012; Haag, 2012; "Megalonaias nervosa", 2014)


The washboard's habitat consists of large slow moving rivers systems that include adjacent tributaries and drainage basins. This mussel is most commonly found in the Mississippi River. The washboard is adapted to use a wide variety of river bottom substrates such as mud and rocks, but this mussel prefers to live on gravel or sandy river bottoms. ("Megalonaias nervosa", 2014)

  • Aquatic Biomes
  • benthic
  • rivers and streams
  • Range depth
    15.25 (high) m
    50.03 (high) ft

Physical Description

Shells of the Megalonaias nervosa are rectangular and covered with loops and folds, which makes the washboard look much different from other mussels. Young washboards are known to have fine ridges and folds. These ridges and folds become more apparent as the mussel ages. The outer shell of the mussel is known as the periostracum. Proteins within the periostracum is what gives the washboard its black or brown coloring. The inner surface of the shell is white and known as the nacre. The mussel also exhibits psuedocardinal teeth. ("Megalonaias nervosa", 2011; Haag, 2012; "Megalonaias nervosa", 2014)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    263.8 (high) g
    9.30 (high) oz
  • Range length
    40 to 250 mm
    1.57 to 9.84 in


After fertilization, the eggs of Megalonaias nervosa move to the female's gills and reside there until the eggs hatch into larvae commonly known as glochidia. As a glochidia, the washboard leaves the female's gills and attaches to the gills of fish. The three most common fish that Megalonaias nervosa attaches to are the flat headed catfish, white crappie and bluegills. Once attached to the fish, the glochidia finish larval development. After larval development is complete, the young washboards release from the gills of the fish and land on the river bottom to mature into adults. Throughout their adult life, the mussels continue to grow. ("Megalonaias nervosa", 2011; Haag, 2012; "Megalonaias nervosa", 2014)


For reproduction, the male Megalonaias nervosa releases sperm into the water and the female Megalonaias nervosa uptakes the sperm into her incurrent siphon. The spawning behavior of Megalonaias nervosa is dependent of the temperature of river water. The river water cooling down in the fall is what cues washboards to begin their mating process. ("Megalonaias nervosa", 2011; Cummings and Graf, 2009; Haag, 2012; "Megalonaias nervosa", 2014)

After the female's eggs are fertilized, the female washboard keeps the eggs in her gills for development. The size of washboard larvae is extremely small, ranging from 50 µm to 450 µm. After finishing development, the female washboard begins to attract fish to finish the embryo development process. The embryos of washboards have a parasitic relationship with fish. A grouping of parasitic washboard larvae is known as a glochidia. A female attracts fish using a her mantle as a lure. Once the fish moves close enough while investigating the mantle bait, the female releases her glochidia for the larvae to attach to the fish's gills. The larvae finish development in the gills of fish before turning into an adult. Larger female washboards typically have higher fecundity rates than smaller female washboards. ("Megalonaias nervosa", 2011; Cummings and Graf, 2009; Haag, 2012; "Megalonaias nervosa", 2014)

  • Breeding interval
    Washboard individuals breed only once a year.
  • Breeding season
    Spawning takes place in early fall.
  • Range number of offspring
    1,000 to 1,000,000
  • Range age at sexual or reproductive maturity (female)
    3 to 9 years
  • Average age at sexual or reproductive maturity (female)
    8 years
  • Range age at sexual or reproductive maturity (male)
    3 to 9 years
  • Average age at sexual or reproductive maturity (male)
    8 years

Males provide no parental care, but females do invest a significant amount of energy. Female carry the fertilized eggs for a short while until they hatch into glochidia. The female uses her mantle as a lure to attract a host fish, and when the fish draws near enough, the female washboard releases the glochidia, which are parasitic and attach to the host fish. The glochidia continue their development on the fish, independent of the female parent. (Cummings and Graf, 2009)

  • Parental Investment
  • pre-hatching/birth
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female


The oldest recorded washboard was 54 years of age. Typically, washboards on average live between 30 to 40 years. ("Megalonaias nervosa", 2011; Cummings and Graf, 2009; Haag, 2012)

  • Range lifespan
    Status: wild
    54 (high) years
  • Typical lifespan
    Status: wild
    30 to 40 years


Megalonaias nervosa is a solitary species that does not have very much interaction with other species after maturity. Mussels are sedentary creatures, but can maneuver around using their foot that extends out between the two halves of the shell. The washboard normally moves about during changes in water levels to the rivers. (Haag, 2012; "Megalonaias nervosa", 2014)

Communication and Perception

Megalonaias nervosa typically lives in groupings of other mussels. They respond to strong cues from the environment when it comes to mating practices. In particular, water temperature is what cues the washboard to mate. Otherwise there is no further communication. (Haag, 2012)

Food Habits

Washboards are filter feeders that eat algae, bacteria, protozoans and other organic material. This mussel accomplishes this by taking in water through the incurrent siphon by filtering out food as the water passes through. Both food and oxygen are removed as the water passes through the washboard's gills. Waste from this process is removed by the excurrent siphon. Tiny hair-like particles called cilia move the food up from the gills to the mouth. ("Megalonaias nervosa", 2011; Haag, 2012)

  • Plant Foods
  • algae


Humans are the largest predator of Megalonaias nervosa. Other predators for this mussel include muskrats, raccoons, waterfowl and some fish. ("Megalonaias nervosa", 2011; Haag, 2012; "Megalonaias nervosa", 2014)

Ecosystem Roles

Like other freshwater mussel species, Megalonaias nervosa is a parasite during the early larval stage of life. The larvae of washboards, known as glochidia, live as parasites on fish until larval development is complete. Some fish hosts include flat headed catfish, white crappie and bluegills.

Zebra mussels (Dreissena polymorpha) are known to attach themselves to Megalonaias nervosa, causing the washboard to suffocate and die. Washboards also serve as prey to a variety of vertebrates, such as raccoons and muskrats. This mussel helps with water clarity in numerous river systems during its adult life, by filtering particles out of the water. ("Megalonaias nervosa", 2011; Clayton, 2012; Haag, 2012)

Species Used as Host

Economic Importance for Humans: Positive

Megalonaias nervosa is harvested for their shells. In the pearl industry the washboard's shell is highly valued for the white nacre. The white nacre is used in the production of pearls. Historically, buttons for clothing were made out of washboard shells. This process was extremely wasteful of this species and no doubt has contributed to the decline in this species today. ("Megalonaias nervosa", 2014)

  • Positive Impacts
  • body parts are source of valuable material

Economic Importance for Humans: Negative

There are no known adverse effects of Megalonaias nervosa on humans. ("Megalonaias nervosa", 2014)

Conservation Status

Megalonaias nervosa is currently a threatened species in numerous states around the U.S. Destruction of habitat is one of the largest factors to the washboards decrease in population size in these states. Pollutants, damming of streams, increased siltation and blockage of host fish migration contributes to this problem. Additionally, Dreissena polymorpha, commonly known as the zebra mussel, attaches to the shell of washboards, killing them by suffocation. The washboard is also harvested for the pearl industry, contributing to its population decrease.

Megalonaias nervosa is listed as a species of "least concern" by the IUCN, and has no federal conservation status. This status may need to be reviewed in light of the habitat destruction occurring in some states. ("Megalonaias nervosa", 2011; Clayton, 2012; Cummings and Graf, 2009; Haag, 2012)


Kathryn Brekken (author), Minnesota State University Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Angela Miner (editor), Animal Diversity Web Staff.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


Referring to an animal that lives on or near the bottom of a body of water. Also an aquatic biome consisting of the ocean bottom below the pelagic and coastal zones. Bottom habitats in the very deepest oceans (below 9000 m) are sometimes referred to as the abyssal zone. see also oceanic vent.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


particles of organic material from dead and decomposing organisms. Detritus is the result of the activity of decomposers (organisms that decompose organic material).


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


union of egg and spermatozoan


a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.


mainly lives in water that is not salty.


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

internal fertilization

fertilization takes place within the female's body


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death


an animal that mainly eats plankton

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


2011. "Megalonaias nervosa" (On-line). EOL Encyclopedia of Life. Accessed April 12, 2014 at

Minnesota Department of Natural Resource. 2014. "Megalonaias nervosa" (On-line). Minnesota Department of Natural Resources. Accessed March 20, 2014 at

Clayton, J. 2012. "Mussel Restoration in West Virginia Streams" (On-line). Accessed April 23, 2014 at

Cummings, K., J. Cordeiro. 2011. "Megalonaias nervosa" (On-line). The IUCN List of Threatened Species. Accessed March 20, 2014 at

Cummings, K., D. Graf. 2009. Ecology and Classification of North American Freshwater Invertebrates. Italy: Academic Press.

Haag, W. 2012. North American Freshwater Mussels. New York: Cambridge University Press.

Haggerty, T., J. Garner, R. Rogers. 2005. Reproductive phenology in Megalonaias nervosa (Bivalvia: Unionidae) in Wheeler Reservoir, Tennessee River, Alabama, USA. Hydrobiologia, 539: 131-136. Accessed March 20, 2014 at

Klocek, , Bland, Barghusen. 2008. "Washboard" (On-line pdf). Accessed March 20, 2014 at

Woody, C., L. Holland-Bartels. 1993. Reproductive characteristics of a population of the washboard mussel Megalonaias nervosa (Rafinesque 1820) in the upper Mississippi River. Journal of freshwater ecology. La Crosse, WI, 8/1: 57-66. Accessed March 20, 2014 at