Excellent photos. Thank you!

One of the species is amphiatlantic (Littorina obtusata) and personally 
I know that species from mary places on the European Atlantic and North 
Sea coasts, and the shell morphology of the American specimens really 
looks different to me compared to the European ones (American specimens 
are much less flat than over here). Also: on the European side of the 
Atlantic L.obtusata forms a species complex with L.fabalis. Thus I'm 
wondering if the American L.obtusata are really that species or a 
distinct, but different, member of the species complex.

See also e.g.:

https://bmcecolevol.biomedcentral.com/articles/10.1186/s12862-019-1561-6

Sincerely, Erick

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