You may recognize this if you live on the east coast of the U.S. south of Cape Cod: it’s a whelk egg string. Here in the NYC region, we have two types of big whelks, the channeled and the knobbed. The knobbed is the state shell of New Jersey and Georgia, should you ever be asked. (State shells?) Down south, you may also come across the lightning whelk and the pear whelk. Up north in the New England states north of Cape Cod, fugetaboutit!
The string pictured was found on Nantucket. It’s from a knobbed whelk. I grew up seeing these things on the beach, but it was not until last year that I learned that the individual cases on the string can be full of tiny whelks.
Yes, these are in the palm of my hand; the sand (which spilled out with them) is also for scale. What you see is the contents of just one of the coin-sized cases on the string. Successful whelks can grow to be 5-9 inches long.
UPDATE: The search term feature of WordPress allows me to see the words and phrases that lead people to this site. “My dog ate a whelk egg case” was one. The strings look and feel pretty crunchy, but I think the dog will be OK. I used to know a dog that ate shampoo and soap and he was OK, albeit crazy.
Backyard and Beyond 
Fantastic. I never knew about the tiny whelks inside. Thanks.
Love those, even if my ears are too big to hear all their little voices.
I bet they all say, like Xenophone’s Greeks, “Thalatta, thalatta!”