Animal Diversity Web

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)

• Biogeographic Regions
• nearctic
  • native

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)

• Habitat Regions
• freshwater

• 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)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• 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)

• Development - Life Cycle
• metamorphosis

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)

• Mating System
• polygynandrous (promiscuous)

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)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
  • internal

• 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)

• Key Behaviors
• parasite
• motile
• sedentary

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)

• Communication Channels
• chemical

• Perception Channels
• tactile
• vibrations
• chemical

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)

• Primary Diet
• planktivore
• detritivore

• Plant Foods
• phytoplankton

• Other Foods
• detritus

• Foraging Behavior
• filter-feeding

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)

• Known Predators

  • Ducks
  • Herons
  • Fish
  • Racoons, Procyon lotor
  • Muskrats, Ondatra zibethicus

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)

• Ecosystem Impact
• parasite

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)

• IUCN Red List

  Vulnerable

• US Federal List

  Endangered

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

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

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.