One of the mussel species that is quite common in New Brunswick streambeds is the eastern pearl shell mussel (Margaritifera margaritifera). It happens to have a thicker layer of nacre than most species. This mussel was also abundant in Europe in feudal times. In this period, royalty owned the rivers and would have workers gently pry open the shell of the mussel to see if a pearl was present. If there wasn't, the mussel would be placed back in the river.