The strand of half dollar sized pods is an egg case. Actually each pod has about twenty tiny animals in each pod.
The tiny animal that will grow from this egg case is the knobbed whelk. This is basically a northeast version of a conch (pronounced conk). If you hold the tiny discs up to the sunlight you can see the tiny versions of the whelk developing.
The whelk is a mollusk (like clams and oysters) but only has one shell. This shell grows with the whelk as it gets older – as opposed to the hermit crab which moves out as it gets bigger.
Also, if you hold the whelk shell up to your ear you can hear the ocean. Lastly, do not hold up a whelk shell to your ear if it has a tough protective “door” covering its opening. That’s the mantle and means that an animal inhabits the shell. Please place it right back where you found it.
Image (c) Jo O’Keefe.
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Thanks for posting this. My friend and I were wondering what those were, and thanks to the power of Google and your blog, we now know. I remember seeing these on the beaches of New England when I was a kid, but none of us knew what they were.