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Pyganodon grandis
Giant Floater - photo by Bob Gress


Pyganodon grandis

This is perhaps the most common large species of mussel in Kansas.  Its shell typically reaches a length of 150 mm (6 inches) in length in our area.  It has been recorded as large as 10 inches in the upper Mississippi valley.   It prefers mud-bottomed bodies of water with little or no current.  It may be found from very shallow areas down to 20 feet deep.

Giant Floater
Thin-shelled morph of Pyganodon grandis
- photo by Jim Mason

It occurs in two different versions.  One has a very thin shell.  The other (see above) is much thicker.  The shape of the shell is also divergent with some being blunt at the posterior end and others being more oblong with a pointed posterior end.  2 - 3 year old individuals often have fine green rays, as is seen in the photo of the thin-shelled morph.  They become dark brown with age.   These extreme variations in shell shape and thickness have confounded authorities for years.  The variance may be a response to differences in current and bottom substrate or it may just be genetic.  In either case the giant floater has a very inflated or "fat" look to it.

Pyganodon teeth
Hinge line of Giant Floater - photo by Jim Mason

A key characteristic of the giant floater is the absence of either lateral or pseudocardinal teeth.

This is a bradytictic species, forming embryos in fall and releasing the glochidia in late winter/early spring.  It uses a wide variety of fish species as hosts for its glochidia including freshwater drum and various gar, catfish and sunfish.

RANGE AND STATUS IN KANSAS:  Because of its wide habitat tolerances, it is one of the few species of mussel found in the western half of Kansas.  It is absent only from the extreme western counties where permanent water bodies are not present.  For more information and a distribution map, see the species entry in the Mussel BedSTABLE

RANGE AND STATUS IN NORTH AMERICA:  The giant floater is found throughout the Great Plains from the lower Rio Grande valley to Manitoba and east to Quebec, Ohio and Alabama.  STABLE

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Great Plains Nature Center
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