MetaFilter

Late writers report, that not only in Scotland, but in the River of Thames also by London, there is a kind of shellfish in a two-leafed shell, that has a foot full of plaits and wrinkles. These Fish are little, round, and outwardly white, smooth and brittle shelled, like an almond shell, inwardly they are great bellied, bred as it were of moss and mud. They commonly stick on the keel of some old ship, where they hang together like mushroom stalks, as if there were thereby nourished. Some say, they come of Worms, some of the boughs and branches of trees which fall into the sea, if any of these be cast upon shore, they die; but they which are swallowed still into the sea, live, and get out of their shell, and grow to be Ducks or such like Birds.