My understanding (though I do not have a reference) is that Crepidula
fornicata was accidentally imported to England along with Crassostrea
virginica intended for oyster farming. It then crossed the Channel,
probably not requiring assistance, and has become a nuisance in many oyster
beds. I heard that some people took up eating Crepidula instead.
The species name is derived from fornix, an arch.
David C.