Alasmidonta marginata



  • size: small to medium. maximum 140 mm, but most under 70 mm.
  • thickness: thin to moderately thick.
  • shape: trapezoidal, wedge-shaped in cross-section, with relatively flat posterior slope bordered by a sharp posterior ridge, giving it a distinctive truncated look. mostly straight ventral margin
  • width: moderately to very inflated
  • surface: smooth. posterior slope with many fine ridges/creases
  • beaks: pronounced double loops, usually dissolved/abraded
  • color/markings: greenish with dark rays that are punctuated with numerous darker spots. Occasionally spots very few or entirely absent. Wider and darker rays common close to posterior ridge.
  • sexual dimorphism: none
  • pseudocardinal teeth: rudimentary or weakly developed, lamellar
  • lateral teeth: none. thickening of the hinge line
  • nacre: white

Soft parts: foot bright orange, more rarely peach.

Similar species/lookalikes: usually unmistakable in the field, even as weathered shells. Young live spotless specimens can resemble young creepers, Strophitus undulatus.


Lake Huron-St-Clair dr.:

  • Saugeen R.
  • Ausable R.
  • Maitland R.
  • Sydenham R.
  • Thames R.
    Lake Erie dr.:

  • Grand R.
    Lake Ontario dr.:

  • Moira R.

- Salmon R.


  • Ottawa R. < Noire R. (Pontiac), Rouge R.(Argenteuil), < Rivière-des-Prairies (Montreal)
  • L'Assomption R. < Ouareau R.
  • Yamaska R.
  • St-Francois R.
  • Nicolet R.
  • Bécancour R.

Habitats and habits 7

This is a small to medium river species, typically found in riffle and other fast water areas but also frequents larger rivers in very low densities. Usually buried deep enough as to be visually inconspicuous, it seems to vertically migrate up from the substrate in early and late summer. It is said to be more sensitive to water quality degradation than most freshwater mussels, but seemingly healthy populations have been found in rivers significantly affected by agricultural runoff. This species is possibly more common than currently estimated, due to it's secretive nature.

Conservation status 7

The elktoe is currently classified "of special concern" in Quebec, where it's restricted range is currently under review. No status in Ontario, and does not occur in other provinces.

Sources and Credits

  1. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/5936097
  2. (c) Matthew Ireland, some rights reserved (CC BY-NC), http://inaturalist.ca/photos/7598255
  3. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/12186691
  4. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/12186692
  5. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/10831838
  6. Adapted by Philippe Blais from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Alasmidonta_marginata
  7. (c) Philippe Blais, some rights reserved (CC BY-SA)

More Info

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