Triangle Floater

Alasmidonta undulata

Diagnostics 13

SHELL

  • size: small to medium. Maximum 85 mm, but most under 50 mm
  • thickness: very thick in anterior, thin in posterior with abrupt mid-shell transition
  • shape: oval to ovoid, with posterior more pointed in large individuals. Old, large individuals may have open gap in foot area when shell is fully closed
  • width: very inflated,
  • surface: smooth
  • beaks: elevated and anterior. umbonal cavity deeply set, reaching under pseudocardinals (best viewed facing posterior end) . sculptures: very thick and large single loop bars, the most pronounced of all our native unionids
  • color/markings: brownish to greenish with dark green rays throughout. Older shells uniform and very dark.
  • sexual dimorphism: none
  • pseudocardinal teeth: very strong, often with pronounced serrations ("teeth on teeth"), especially in hard water habitats
  • lateral teeth: vestigial. slanted folds radiating from beaks
  • nacre: white in posterior, bluish and iridescent in anterior.

Soft parts: foot white or peach

Similar species/lookalikes: usually distinct. The deep umbonal cavity with it's deepest point only visible from a posterior viewpoint is a reliable criteria for quick identification in specimens where the diagnostic extra heavy beak sculptures are dissolved beyond recognition. The pronounced serrations on the pseudo-cardinals is also a telltale feature, when present.

Sources and Credits

  1. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/12771164
  2. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/31988639
  3. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/31988640
  4. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/31988641
  5. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/31988643
  6. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/31988644
  7. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/79279631
  8. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/79279657
  9. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/78848765
  10. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/78849681
  11. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/74937187
  12. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/74937200
  13. (c) Philippe Blais, some rights reserved (CC BY-SA)

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