Come out of your shell.

That is easier said than done if you are a bivalve. Bivalves are two-shelled animals that live in marine and fresh water environments. The word bivalve connotes “two leaves of a door,” which refers to its two-sided, or double-shelled, form.

One reason that a bivalve might not want to come out of its shell could be the fear of what’s outside: people’s (and other animals’) propensity to devour them. Included in the bivalve group are some of the world’s finest eating shellfish, such as oysters, clams and mussels.

But there is another bivalve that is safe from the cocktail sauce. Jingle shells will never be made into chowder, though they sound as if they belong in a Christmas carol and garner as much attention at the beach as the grandest holiday tree laden with gifts.

Jingle shells won’t tempt you with a delicious flavor, because they are known to have quite a bitter taste. Even Euell Gibbons, who staked (and ‘steak-ed’) his fame on eating almost every marine animal available, ignores the jingle shell, not even mentioning it in his famous tome on wild edibles of the sea and shore, Stalking the Blue-Eyed Scallop.

Though one may be able to disregard jingle shells as a possible meal, it is impossible to deny the intrigue and beauty or this unique bivalve.

Jingle shells come in many colors, including yellow, orange, silver and black. The shell can be as large as a quarter, and is thin, almost paper-like, and translucent. It is a seaside treasure familiar to most beachcombers. And although single shell halves are almost always found by themselves, remember that they come from a bivalve, and, as a bivalve, that jingle shell originally had two halves that were hinged together to hold an animal within.

Those two shells that were once connected by a hinge at the top are not identical twins. Each half of the shell has its own form and function. The lower shell is usually flat, and has a hole in the top where the animal’s byssal threads grow out to attach it to another surface. Jingle shells can lay claim to a rare and specific zoological term: They are called “epifaunal,” which means that they attach to rocks or other shells. There’s more though, as they also (and here’s the interesting part) take the form of what they grow on.

Look for scalloped or ridged jingle shells that grew on and took the shape of a scallop shell. The rounded jingle shells most often collected from the beach are the top shells — which, not needing to mold themselves to the contour of the surface below, simply grow concave.

And where does the name “jingle shell” come from? It describes the sound they make when a few of them come together (outside the water, of course). They have been made into jewelry, wind chimes and even lampshades due to their delicate beauty and appealing sound.

Jingle shells are also called mermaid’s toenails, though I always imagined that mermaids had fins, not toes. They were more plausibly called Neptune’s toenails, which is another of their aliases. Perhaps sand dollars, fool’s gold, fool’s platinum, or fool’s silver might be appropriate nicknames, too, because one can’t help feeling you’ve come across a special piece of treasure from the ocean when you spy one of these pearl-slices (another possible nickname) lying on the beach. The next time you pick one up, contemplate the circumstances that brought this half of a highly adaptable, attractive but unpalatable bivalve out of the ocean and into your hand.

Suzan Bellincampi is director of the Felix Neck Wildlife Sanctuary in Edgartown.