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Here’s what you’ll learn when you read this story:

  • In 2023, a National Oceanic and Atmospheric Administration (NOAA) expedition off the coast of Alaska discovered an inexplicable “golden orb” and had no idea what it could be.

  • Three years of analysis has revealed that the orb is actually remnant of a secreted cuticle that allows the strange sea anemone Relicanthus daphneae to attach itself to a rocky substrate.

  • Discovering the answer required genomic analyses across a variety of disciplines, including morphology, genealogy, and bioinformatics.

While the frontiers of human exploration often look toward the stars, some of that attention should also be spent exploring Earth’s oceans. According to the U.S. Geological Survey, we have better maps of the surface of Mars than we do of our planet’s own ocean floor, and expeditions exploring the depths of our aquatic terrain regularly turn up head-scratching mysteries.

One of those scientific puzzles appeared during a National Oceanic and Atmospheric Administration (NOAA) expedition off the coast of Alaska when scientists spotted what could only be described as a shiny golden orb. The moment of discovery was captured by a crew aboard the Okeanos Explorer during a livestream of the Seascape Alaska 5 expedition, which was mapping some of the deepwater habitats in remote regions of Alaska’s coastline.

“I don’t know what to think about that,” one of the researchers could be heard saying. “I would love to poke it and see how hard it is,” said another researcher.

Now, in a new study uploaded to bioRxiv, scientists from NOAA fisheries and the Smithsonian National Museum of Natural History explain how they studied the sample’s structure and DNA to confirmed that this golden “egg” wasn’t some preamble to a deep-sea horror story. Instead, it’s part of the base of a giant sea anemone.

The anemone in question is Relicanthus daphneae, one of the weirder animals found in Earth’s oceans. First discovered in the 1970s, R. daphneae is uncommonly large for a sea anemone, as its tentacles can stretch up to seven feet long in some cases. For the past 20 years, scientists have gone back and forth about its taxonomic status. In 2014, a DNA analysis suggested the animal belonged in an entirely new order, but a future study including some of the same researchers revised that opinion and instead decided that the on-again, off-again anemone belonged in its own suborder (Helenmonae), of which it remains the only species.

“This turned into a special case that required focused efforts and expertise of several different individuals,” NOAA fisheries’ Allen Collins, a co-author of the study, said in a press statement. “This was a complex mystery that required morphological, genetic, deep-sea and bioinformatics expertise to solve.”

Step one was nixing the idea this was some kind of animal itself. It was immediately apparent that the object contained no animal anatomy of any kind, but the layered surface did contain cnidocytes, a kind of stinging cell found in the phylum Cnidaria, which contains corals and anemones. Further analysis drilled deeper, discovering that these cells were spirocysts, meaning this “orb” belonged to some member of the group Hexacorallia. It wasn’t until whole-genome sequencing, specifically mitochondrial genomes, determined that the animal DNA must belong to R. daphneae. It’s likely that the golden orb itself is the remnant of a secreted cuticle that allows the anemone to anchor itself to a rocky substrate.

“This is why we keep exploring,” acting director of NOAA Ocean Exploration William Mowitt said in a press statement, “to unlock the secrets of the deep and better understand how the ocean and its resources can drive economic growth, strengthen our national security, and sustain our planet.”

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