The most common guesses include a geode, a misshapen pomegranate, and a “period rock.” But all these guesses are wrong.
Scientific American’s Becky Crew explains that this bizarre-looking specimen is actually a sea creature (Pyura chilensis, to be exact, but known less formally as a “sea squirt.”) It’s commonly found in the coastal waters of Chile and Peru. They don’t look like much from the outside — their squishy bits are encased in a thick substance called “Tunicin” that’s very similar to the cellulose that you find in plants — but slice one open, and you’ll see they’re actually quite beautiful, if a little alien-looking.
But that’s not the only thing odd about P. chilensis. Despite its crimson appearance, this creature has clear blood. Its meat contains the rare element vanadium, in concentrations up to 10 million times that of the ocean waters where it makes its home (nobody’s quite sure why this is.) And it possesses both male and female gonads. They’re also, evidently, delicious. But while P. chilensis have been fished commercially by Chilean and Peruvian natives for years, it wasn’t until 2005 that researchers had a clear idea of this bizarre animal’s mating habits.