Eastern Elliptio

Elliptio complanata

Diagnostics 8

SHELL

  • size: mid-sized to large, maximum 150 mm. most under 100 mm
  • thickness: moderate thickness to thick
  • shape: VERY VARIABLE. most specimens oval-elongate to trapezoidal , but ranges from quite elongate to squat. posterior ridge subtle to pronounced. ventral margin relatively straight to gently rounded, occasionally slightly concave towards posterior, especially in large specimens. posterior end often hooked downwards in older animals.
  • width: compressed to moderately inflated, mostly in posterior
  • surface: smooth to very rough
  • beaks: slightly elevated to nearly even with hinge line. sculptures: 4 to 6 distinct single loops, parallel to growth lines. often prematurely dissolved in most specimens
  • color/markings: yellow-tan to very dark brown, a chestnut shade being most common. faint green rays common in juveniles, less so in adults, occasionally heavy, irregularly spaced green rays in adults in some localities. Periostracum occasionally irridescent in specimens from sandy or muddy habitats.
  • sexual dimorphism: none
  • pseudocardinal teeth: well developed, striated
  • lateral teeth: well developed
  • nacre: most commonly purple, but occasionally pink, salmon or more rarely white or even gold in some localities

Soft parts: foot usually white, rarely bright orange

Similar species/lookalikes: With all its very variable characteristics, this taxon can be a great imitator. Average size, shell thickness and color are extremely variable depending on water quality and hardness of habitat. Live adults can especially be easily be confused with flutedshell specimens with subtle or absent posterior slope corrugations, as both taxons often share the same habitats. Weathered shells of E. complanata that have lost their purple nacre color can be readily identified by the well developed lateral teeth, which are lacking in L. costata. Those same criteria can be applied to differentiate from the Eastern pearlshell, Margaritifera margaritifera, but this taxon is rarely found in the same habitat as E. complanata.
Most confusing, in both live and dead state, when compared with the two other Canadian members of the genus, E. crassidens and E. dilatata, due to it's extremely variable shell length and morphology, a trait also shared to a lesser extent by these other two taxons. however, both of these taxons usually have older ventral growth lines at an angle with more recent ones, whereas Eastern Elliptios usually show proportional, harmonious growth lines throughout life, causing ventral margin lines to be relatively parallel, not angled.
A full spectrum of inter-grades occurring in some localities where these taxons coexist makes reliable identification challenging at best.
Future genetic studies are needed to help resolve this taxonomic morass.

Sources and Credits

  1. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/27396774
  2. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/12696931
  3. (c) Matthew Ireland, some rights reserved (CC BY-NC), http://inaturalist.ca/photos/9210117
  4. (c) Philippe Blais, some rights reserved (CC BY-NC-ND), https://www.inaturalist.org/photos/9541080
  5. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/12696517
  6. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/12696660
  7. (c) redgarter, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais, https://www.inaturalist.org/photos/35175999
  8. Adapted by Philippe Blais from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Elliptio_complanata

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