Leeneina, of course there are the odd Americans who read (past tense, out-dated now) English mysteries (Christie and Sayers excepted), and read them (present tense)- I am one- but I was speaking of the great majority (dare I say 90+%?) who have never heard of a winkle. As an amateur malacologist, I have, but would most wonder if it is, perhaps, a small wrinkle?). Then there are crossworders and scrabblers (my wife suffers from this syndrome), peculiar people all.
On travels to jolly old, I have met with plaice (Pleuronectes), like sole a genetically confused and lop-sided thing, but no one introduced me to a winkle.