Given that Z.nitidus has been described by Müller in 1774 from material
collected at a quite specific location: Denmark: Fridrichsberg near
Kopenhagen (source:
http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/speciestaxon?id=6483
).
Fridrichsberg (at the moment called Frederiksberg) is anno 2012 a
western suburb of Copenhagen, but inland. Even if the species would have
been introduced from the New World by shipping into Europe, it would
have established itself over a very large part of Europe, even to Greece
and deep into Russia, in the 350 year period from the discovery of the
New World by Europeans until the start of consistent faunistic  studies
of terrestrial mollusca in Europe.
For a terrestrial snail, that is highly unlikely. Therefore Z.arboreus =
Nearctic, Z.nitidus = Holarctic with possible introductions by man into
the New World.

Sincerely, Erick




On 12/11/2012 03:39 AM, Harry Lee wrote:
> /Zonitoides arboreus/ is certainly a New World species. /Z. nitidus/
> needs further scrutiny in that regard.
>
> Harry
>
>
> At 07:59 PM 12/10/2012, you wrote:
>> L.s.,
>>
>> Analysis indeed correct but some species are yet missing and need to be
>> added to the list by David:
>>
>> other recent introductions in Western Europe from the New World:
>>
>> Geukensia demissa - recent introduction into W.Europe (probably via
>> ballast water) - in W.Europe locally a plague in brackish water.
>>
>> Mercenaria mercenaria - recent introduction on purpose into W.Europe
>> (local attempts to breed this species, and escaped locally into the
>> wild. S.W.Netherlands, Brittany)
>>
>> Crassostrea virginica - recent introduction on purpose into W.Europe
>> (local attempts to breed this species, and escaped locally into the
>> wild. S.W.Netherlands, Brittany). Is being replaced rapidly by the
>> Pacific oyster, which adapts much better to the W.European marine
>> environment.
>>
>> Ensis directus (or Ensis americanus) - probably introduced via ballast
>> water and at the moment almost a plague in the (sandy) S.E. part of the
>> North Sea. Has become a staple food for molluscivore birds and fishes in
>> the North Sea.
>>
>> Petricola pholadiformis - old introduction, first collection on Dutch
>> coast around 1923. Probably via shipping. Has been constantly common
>> ever since.
>>
>> possibly the Zonitoides could be an introduction from the old world into
>> the new world, since Zonitoides is a quite common genus over here.
>>
>> All species above have been collected by most shell collectors in The
>> Netherlands (myself included) since these are quite common (for
>> Mercenaria and C.virginica, you have to know specific locations).
>>
>> Sincerely, Erick
>>
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