Weird little things on my towel

A few summers back I had these weird things show up on my towel at the cottage. They were some kind of shell thing, hard and crunchy. They were tiny. That's part of my finger in the background. Some were open, some were closed. I think something was hatching out of them. If I knew what a barnacle looked like, I could maybe say they looked like that. Or maybe more like some of the things growing on Bootstrap Bill Turner's face during his time on the Flying Dutchman. Were those barnacles? Anyway, I scraped them off and washed the towel and haven't seen them since. Click for the supersize.