The Sand Octopus Was Hiding in Plain Sight

And yet it took a 19th-century naturalist, a 21st-century grad student, and some Brazilian fishers to crack the mystery.

A sand octopus
Manuella Dultra

The crinkly form of a small, dried octopus lay on a desk in Washington, D.C., 170 years ago. The curious cephalopod, which had been collected more than 7,000 kilometers away in Brazil, was one of thousands of creatures obtained by researchers on the United States South Seas Exploring Expedition, which had taken explorers, navy men, merchants, and scientists on an epic voyage around the Pacific Ocean. The project took years, and some preserved specimens—including a few small-headed red octopuses with white, leopard-like spots that had been picked up from a fish market in Rio de Janeiro, and from local fishers—eventually wound up with experts, such as American naturalist Augustus Addison Gould, for scientific analysis.

A seasoned taxonomist who had cataloged countless mollusk species, from sea snails to bivalves, Gould was convinced that what he had in front of him was a species new to science. He called it Callistoctopus furvus.

But Gould’s work soon faded from memory, and the existence of C. furvus became the subject of dispute. Specimens that Gould had used for his identification went missing, and researchers began to question whether his description of the animal was enough to verify that it truly was a distinct species. Even as recently as a few years ago, biologists could come to little agreement as to whether the octopuses in the Americas that roughly match his report should be classed as C. furvus, or whether they’re really just C. macropus, a similar species found thousands of kilometers away in the Mediterranean Sea.

Altogether, it would take nearly two centuries and—yet again—the help of local fishers for the riddle of Gould’s missing octopus to be solved.


Roughly 10 years ago, Manuella Dultra, a graduate student at the State University of Santa Cruz in Brazil, was hunting for information about octopuses in Brazil’s Bahia state. Local fishers kept telling her about a strange species that only appeared in shallow waters when the wind changed and blew from the east. Dultra’s curiosity was piqued. She asked the fishers to tell her if and when they caught sight of the creature, and to send pictures or video evidence if they could.

In 2013, a fisher captured one of the octopuses and sent it to Dultra. The staff at Brazil’s Federal University of Rio Grande do Sul classified it as C. macropus—but Dultra was unconvinced.

“The information available on the Callistoctopus macropus octopus did not accurately describe the species we were studying,” she says by email. For instance, the local Brazilian octopus had a significantly smaller and narrower head than its Mediterranean brethren.

Dultra launched an investigation hoping to settle the octopus’s identity once and for all. Years of work ensued. She turned again to local fishers, befriending them and learning more about their craft. Among those willing to help with her research was Braz Santos de Oliveira, a fisher in the coastal village of Morro de São Paulo.

For 20 years, de Oliveira has practiced free diving: holding his breath and using a spear to catch fish to eat or sell. He also uses a J-shaped iron bar called a bicheiro to catch octopuses and retrieve fishing nets. He told Dultra how the octopus that interested her was easier to find whenever a new moon was rising—and that, when disturbed, this octopus would often bury itself in the sand. Dultra soon learned from fishers like de Oliveira that the local name for the species means “sand octopus”, whereas another species found in the area, Octopus insularis, is nicknamed the “stone octopus” because it prefers to hide among rocks.

Dultra and her colleagues went to great lengths to understand what local people knew about the elusive sand octopus. The researchers tagged along on fishing trips to take photographs and collect live specimens, and they conducted a total of 187 interviews with locals, seeking to plumb their knowledge.

To fully investigate the identity of the sand octopus, the researchers gathered genetic material from their specimens and tried to find a match elsewhere. At first, they came up dry—meaning that this octopus was genetically distinct from other Callistoctopus species, such as C. macropus.

The team was poised to claim the discovery of a completely new species to science—but that was when they learned of Gould’s work all those years ago. They realized that their specimens could be the same as his C. furvus species, but they needed more proof.

Luckily, in 2018, two researchers in Mexico had identified an octopus that they also suspected was Gould’s C. furvus. Those researchers made a drawing of that octopus and collected a genetic sequence. When Dultra compared the genes of Brazil’s sand octopus to this Mexican specimen, they hit a 99 percent match. That linked Gould’s specimen, Dultra’s sand octopus, and the Mexican C. furvus together.

“For more than 150 years this species has been forgotten in the academic community,” Dultra says. “It was a fantastic result for us.”

That’s twice—in both the 19th and the 21st centuries—that local fishers in Bahia have helped scientists uncover information about the cryptic C. furvus.


Dultra and her colleagues’ research is an example of citizen science in action, says Mike Vecchione, a zoologist at the Smithsonian Institution in Washington. He argues that a similar approach could help resolve taxonomic questions about other animals.

“People that work with nature—they’re sort of natural-born taxonomists or naturalists,” he says. “I think it’s an untapped resource that we’re just starting to take advantage of.”

In their paper, Dultra and her colleagues write that they aren’t aware of other cases in which scientists have formally described a new octopus species with the help of local fishers. But there are examples of this happening with other organisms. Take the people of the Solomon Islands, who described a giant rat they called the vika. These reports finally prompted researchers to investigate in depth, and, sure enough, they detailed the species formally for the first time in a study published in 2017.

The fishers of Bahia learned something during Dultra’s study, too. De Oliveira was intrigued to find out that the sand octopus he knew so well was in fact quite rare. As he said to Dultra: “I used to capture this octopus to eat, but not anymore.”


This post appears courtesy of Hakai Magazine.