If importance is the magnitude of ecological effect - for those of us  
in North America in these latter days it's Dreissena - and the shells  
are available in uncountable myriads for those who wish to collect them.

fred.
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           Frederick W. Schueler & Aleta Karstad
       Mudpuppy Night - http://pinicola.ca/mudpup1.htm
Vulnerable Watersheds - http://vulnerablewaters.blogspot.ca/
     study our books - http://pinicola.ca/books/index.htm
           RR#2 Bishops Mills, Ontario, Canada K0G 1T0
    on the Smiths Falls Limestone Plain 44* 52'N 75* 42'W
     (613)258-3107 <bckcdb at istar.ca> http://pinicola.ca/
"[The] two fundamental steps of scientific thought - the conjecture  
and refutation of Popper - have little place in the usual conception  
of intelligence. If something is to be dismissed as inadequate, it is  
surely not Darwin [, whose] works manifest the activity of a mind  
seeking for wisdom, a value which conventional philosophy has largely  
abandoned." Ghiselen, 1969. Triumph of the Darwinian Method, p 237.
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