Alasmidonta heterodon

Ge­o­graphic Range

The dwarf wedge­mus­sel, Alas­mi­donta het­erodon, has a dis­con­tin­u­ous range on the At­lantic coast of the United States. Twenty-four pop­u­la­tions of dwarf wedge­mus­sels are found within 12 states from Maine to North Car­olina. This species may have oc­curred in Canada but is likely ex­tir­pated. ("Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

Habi­tat

Dwarf wedge­mus­sels are usu­ally found in wa­ters with slow to mod­er­ate cur­rent that have muddy sand to sand and gravel sub­strate. (Shaw, et al., 2006; Wind­sor, 2012)

  • Aquatic Biomes
  • rivers and streams

Phys­i­cal De­scrip­tion

This fresh­wa­ter mus­sel has a trape­zoidal shell usu­ally less than 45 mm long and 25 mm high. The an­te­rior end of the shell is thick and the pos­te­rior end is usu­ally thin­ner. The pe­rios­tracum, or the outer layer of the shell, is a brown color. In ju­ve­niles red­dish brown col­ored rays of dif­fer­ing widths are vis­i­ble. The most dis­tin­guish­ing char­ac­ter­is­tic of this species is the hinge teeth, with the right valve hav­ing two and the left hav­ing only one. These mus­sels are slightly sex­u­ally di­mor­phic, with the fe­male shell swollen pos­te­ri­orly and more trape­zoidal than the male, and the male shell being more com­pressed, ovate and elon­gated. (Michael­son and Neves, 1995; "Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

  • Sexual Dimorphism
  • sexes shaped differently
  • Average length
    45 mm
    1.77 in

De­vel­op­ment

Dwarf wedge­mus­sel fe­males carry eggs in their gills and re­ceive sperm (re­leased from males) through the gills. After eggs have been fer­til­ized, they de­velop into par­a­sitic bi­valved lar­vae called glochidia. The time needed to de­velop from fer­til­ized eggs to glochia is un­known. The newly formed glochidia are re­leased from the fe­male and into the water where they need to at­tach to a host fish to sur­vive. The glochidia de­velop into ju­ve­niles while at­tached to a host. After meta­mor­pho­sis, a ju­ve­nile mus­sel will be sloughed from its host, where it fur­ther de­vel­ops on the stream/river bot­tom.

The par­a­sitic lar­vae have been found to meta­mor­phose on the fol­low­ing host species: mot­tled sculpin, tes­sel­lated darter, and johnny darter. (Wind­sor, 2012)

Re­pro­duc­tion

This species is a long term brooder that spawns in late sum­mer. The male re­leases sperm out into the water, which float down stream and enter the fe­males gills for fer­til­iza­tion. Fe­males can re­ceive sperm from mul­ti­ple males. The re­sult­ing glochidia are then re­leased by the fe­male into the water. (Michael­son and Neves, 1995; "Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012; Shaw, et al., 2006; Wind­sor, 2012)

The dwarf wedge­mus­sel is a long term brooder that spawns in late sum­mer and then be­comes gravid in the fall and re­leases the glochidia any­where from late March to early June. Start­ing around Au­gust, the males re­lease their sperm into the water which is then car­ried to­wards the fe­males. The fe­males take the sperm in through their gills and they fer­til­ize the eggs. Once fer­til­ized, the eggs are held in the mar­su­pia of the fe­male which be­comes swollen and dark when oc­cu­pied. The eggs are held in the mar­su­pia and re­cieve parental care through the win­ter until they are ready to be re­leased as glochida any­where from March to June. (Michael­son and Neves, 1995; "Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

  • Breeding interval
    The dwarf wedgemussel spawns once a year.
  • Breeding season
    Males release sperm into the water around August.
  • Average gestation period
    8.5 months

Fe­males brood fer­til­ized eggs in the mar­su­pia from seven to 10 months. The lar­vae (glochidia) are re­leased in the spring. ("Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

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

Lifes­pan/Longevity

The av­er­age lifes­pan of a dwarf wedge­mus­sel is ap­prox­i­mately 15 years. (Div. of Wildlife, NJ Dept. of Env. Pro­tec­tion, 2004)

  • Average lifespan
    Status: wild
    15 years

Be­hav­ior

Mus­sels in gen­eral are fairly seden­tary. Slight move­ment down­stream might occur but is not usu­ally noted. Dis­per­sal of the species oc­curs when the glochidia at­tach to their mo­bile fish hosts. ("Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

Com­mu­ni­ca­tion and Per­cep­tion

Mus­sels in gen­eral are re­spon­sive to tac­tile and chem­i­cal stim­u­la­tion. Many sen­sory or­gans are on the mid­dle lobe of the man­tle edge. In the foot, mus­sels have paired sta­to­cysts, fluid filled cham­bers with a solid gran­ule or pel­let. The mus­sels use the sta­to­cysts to ori­ent them­selves.

Union­ids in gen­eral may have some form of chem­i­cal re­cep­tion to rec­og­nize fish hosts.

Glochidia re­spond to both touch, light and some chem­i­cal cues. In gen­eral, when touched or a fluid is in­tro­duced, they will re­spond by clamp­ing shut. (Arey, 1921; Br­usca and Br­usca, 2003)

Food Habits

The glochidia of the species are par­a­sitic on its fish host. Once an adult, the dwarf wedge­mus­sel is a fil­ter feeder, feed­ing on phy­to­plank­ton and de­tri­tous. ("Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

Pre­da­tion

Young dwarf wedge­mus­sels are often con­sumed by birds, such as ducks and herons. Young mus­sels are also eaten by fish. Ma­ture dwarf wedge­mus­sels can be con­sumed by some mam­mals, such as rac­coons and muskrats. (Div. of Wildlife, NJ Dept. of Env. Pro­tec­tion, 2004)

Ecosys­tem Roles

Fresh­wa­ter mus­sels in gen­eral oc­cupy many tropic guilds by feed­ing on de­tri­tous. The mus­sels may also aid in the biodegra­da­tion of plant mat­ter. ("Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life", 2012)

Species Used as Host

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Fresh­wa­ter mus­sels in gen­eral are im­por­tant water qual­ity in­di­ca­tor for streams and rivers. (Wind­sor, 2012)

  • Positive Impacts
  • research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are cur­rently no known ad­verse ef­fects of the dwarf wedge­mus­sel on hu­mans.

Con­ser­va­tion Sta­tus

The dwarf wedge­mus­sel, Alas­mi­donta het­erodon, was list as fed­er­ally en­dan­gered on March 14, 1990. The dwarf wedge­mus­sel was added to the fed­er­ally en­dan­gered list pri­mar­ily be­cause of human im­pacts on its habi­tat and water qual­ity. Some fac­tors in­clude: agri­cul­ture, con­struc­tion, pol­lu­tion, silt de­posits, low oxy­gen lev­els, water level fluc­tu­a­tion, tem­per­a­ture fluc­tu­a­tions, flood­ing, ero­sion, and sil­ta­tion. (Wind­sor, 2012)

Con­trib­u­tors

jill Bowne (au­thor), Rut­gers Uni­ver­sity, pat dzi­amba (au­thor), Rut­gers Uni­ver­sity, David V. Howe (ed­i­tor), Rut­gers Uni­ver­sity, Renee Mul­crone (ed­i­tor), Spe­cial Pro­jects.

Glossary

Nearctic

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

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.

chemical

uses smells or other chemicals to communicate

detritivore

an animal that mainly eats decomposed plants and/or animals

detritus

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

ectothermic

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

fertilization

union of egg and spermatozoan

filter-feeding

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.

freshwater

mainly lives in water that is not salty.

heterothermic

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.

internal fertilization

fertilization takes place within the female's body

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

metamorphosis

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.

motile

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.

parasite

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

phytoplankton

photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)

planktivore

an animal that mainly eats plankton

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

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

tactile

uses touch to communicate

vibrations

movements of a hard surface that are produced by animals as signals to others

Ref­er­ences

Na­ture­Serve. 2012. "Na­ture Serve Ex­plorer: An On­line En­cy­clo­pe­dia of Life" (On-line). Alas­mi­donta het­erodon. Ac­cessed July 06, 2012 at http://​www.​natureserve.​org/​explorer/​servlet/​NatureServe?​searchName=Alasmidonta+heterodon.

Arey, L. 1921. An ex­per­i­men­tal study on glochidia and the fac­tors un­der­ly­ing en­cyst­ment. J. Exp. Zool., 33: 463-499.

Br­usca, R., G. Br­usca. 2003. In­ver­te­brates. Sun­der­land, Mass­a­chu­setts: Sin­auer As­so­ci­ates, Inc.

Div. of Wildlife, NJ Dept. of Env. Pro­tec­tion, 2004. "Dwarf wedge­mus­sel - Au­gust species of the month" (On-line). New Jer­sey De­part­ment of En­vi­ron­men­tal Pro­tec­tion, Di­vi­sion of Wildlife. Ac­cessed July 06, 2012 at http://​www.​nj.​gov/​dep/​fgw/​ensp/​somaug.​htm.

Michael­son, D., R. Neves. 1995. Life his­tory and habi­tat of the en­dan­gered dwarf wedge­mus­sel, Alas­mi­donta het­erodon. Jour­nal of the North Amer­i­can Ben­tho­log­i­cal So­ci­ety, 14 (2): 324-240. Ac­cessed Sep­tem­ber 01, 2012 at http://​fishwild.​vt.​edu/​mussel/​PDFfiles/​wedgemussel.​pdf.

Shaw, K., T. King, W. Lel­lis, M. Eack­les. 2006. Iso­la­tion and char­ac­ter­i­za­tion of mi­crosatel­lite loci in Alas­mi­donta het­erodon (Bi­valvia: Union­idae). Mol­e­c­u­lar Ecol­ogy Notes, 1: 365-367.

Wind­sor, B. 2012. "Dwarf wedge­mus­sel" (On-line). U.S. Fish & Wildlife Ser­vice. Ac­cessed July 06, 2012 at http://​www.​fws.​gov/​northeast/​njfieldoffice/​Endangered/​dwarfwedge.​html.