This is yet another one of those projects that I thought of while doing something completely unrelated to cake decorating; probably driving or doing dishes. I was thinking about the curved petal tips used for piping violets and, well, not much else. It seemed to me they might be the right shape to pipe shells; after looking around on Wikipedia, I figured the exact shell I had in mind was the cockle, a "group of (mostly) small, edible, saltwater clams." Here's all I needed; medium consistency royal icing in a bag fitted with a #61 curved petal tip, parchment paper squares, a flower nail, and a glue stick.
First, stick a parchment square to the nail with a dab from the glue stick.
striped bag or dusted with Pearl Dust.