Freshwater Pearl Mussel
Margaritifera margaritiferaDIAGNOSTICS 4
SHELL
- size: medium to large. maximum 150 mm. most specimens under 100 mm
- thickness: moderate
- shape: elliptic, long, often curved dorsally with a concave ventral margin in adults. The posterior end typically has the same profile as a blunted bowie knife, with its angled posterior slope edge.
- width: compressed to moderately inflated
- surface: smooth; concentric undulations along growths rings are common in early shell, more evident around posterior slope giving a corrugated appearance. Periostracum thick.
- beaks: low, and prematurely dissolved, severely so in older animals; sculptures rarely evident for that reason, even in very young specimens.
- color/markings: uniformly brown to black
- sexual dimorphism: none
- pseudocardinal teeth: slightly wider than hinge plate, sometimes serrated
- lateral teeth: absent to weak and low, on cavity side of hinge plate; single in either valve when present.
nacre: white, with light pink common towards beak cavity. Few to numerous pits in middle of beak cavity, at the ventral end of discrete furrows radiating from umbos, giving a 'meteor shower' effect. Anterior abductor muscle scar very rough, deeply pitted in very old specimens*, with raised branching septae arising from posterior rim (the ''winter hedgerow" sign) in adults, as opposed to radial creases as in most other North American unionids.
(*This feature can sometimes be observed from the outside of the shell in older animals with extremely dissolved umbos)
Soft parts: Inhalant aperture protruding, flared, frilly and often colorful (bluish or purplish inside, rusty orange on edges and on exterior), but shades of earth tones are more common. Exhalant aperture long and floppy. Inter-siphon mantle not fused; gills cream or bluish. Foot beige.
Similar species/lookalikes: shape of live specimens can be very similar to Eastern elliptio, which is occasionally found in the same habitat. But that species always has two well developed lateral teeth in left valve. Most E. complanata usually have a purple colored nacre, but occasionally pale cream or white as in M. margaritifera. Some specimens of E. complanata can also share the kidney shaped shell with a slightly concave ventral edge of most adult M. margaritifera, but never display the concentric, even swellings along growth lines of some younger M. margaritifera.
Mid-shell pitting of the nacre is diagnostic on its own in Eastern Canada, as is the single weak lateral in the left valve, but those inner shell features can be dissolved quickly after death, making weathered shells much harder to clearly discern from equally weathered Elliptio complanata shells. The deeply pitted anterior muscle scar, with raised branching septae is also distinctive, and is often a persistent, readily observable trait even in weathered shells.
The uniquely flared, frilly and colorful inhalant aperture is diagnostic as well for in-situ live specimens, and can sometimes be seen for a good distance from the shoreline.
DISTRIBUTION/DRAINAGES 5
QUEBEC
Ottawa R. dr.:
- R. Kinonge (Argenteuil)
- R. du Nord < R. Doncaster (Laurentians)
R. L'Assomption < R. Ouareau < R. Jean-Venne (Lanaudière)
Saint-Lawrence R. dr.:- R. Bayonne < R. Berthier (Lanaudière)
- R. St-Francois < Ruis. McLeod (Eastern Townships)
- R. Etchemin (Beauce)
- R. Malbaie (Charlevoix)
- R. Du Gouffre (Charlevoix)
- R. aux Saumons (Lac-St-Jean)
- R. Godbout (Cote-Nord)
- R. Matane (Gaspésie)
- R. Sainte-Anne (Gaspésie)
- R. Ristigouche (Gaspésie)
NEW BRUNSWICK
- Kennebecasis R.
- Miramichi R.
- Restigouche R.
- Bouctouche R.
-
NOVA SCOTIA
- Musquodoboit R.
- Stewiacke R.
PRINCE EDWARD ISLAND
- Morell R.
NEWFOUNDLAND
- Daniel's Br.
- Bear Br. Pond
- Bethune's Br.
- Come-by-Chance R.
- Indian R.
Sources and Credits
- (c) Philippe Blais, some rights reserved (CC BY-NC-ND), uploaded by Philippe Blais
- (c) Joel Berglund, some rights reserved (CC BY-SA), http://commons.wikimedia.org/wiki/File:Group_of_Margaritifera_margaritifera.jpg
- (c) btk, some rights reserved (CC BY-ND)
- Adapted by Philippe Blais from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Margaritifera_margaritifera
- (c) Philippe Blais, some rights reserved (CC BY-SA)