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Researchers have described a species of shark new to science, a native of the waters off north-western Australia, all thanks to a set of mysterious, furrowed eggs.

The findings are the culmination of a story that began in 1983 in Rowley Shoals, Western Australia. That August, researchers collected several strange, empty shark egg cases from about 450 metres down. In 1989, researchers found another egg case with an embryo inside it. The cases sported tightly coiled tendrils at their bases and were covered in deep ridges that widen at the edges in a T-shape.

But it wasn鈥檛 until 2011, when the late researcher examined in detail the eggs and embryo 鈥� kept in the Western Australian Museum 鈥� and determined they must belong to some yet undescribed species of demon catshark (Apristurus). These small, shovel-snouted deep-water sharks are poorly understood, says at the聽Commonwealth Scientific and Industrial Research Organisation in Hobart, Australia.

In 2017, when White鈥檚 colleague began studying shark and ray egg cases in the Australian National Fish Collection, two more egg cases turned up that strongly resembled the other mysterious ridged eggs. White, O鈥橬eill and their colleagues compared all the egg cases from known demon catshark species in Australia and nearby regions.

鈥淓ventually, we were able to eliminate all possible species, which suggested we had found something new,鈥� says White.

In 2022, the team looked through the museum collection for whole animal specimens of demon catsharks collected from the same region where the strange egg cases were discovered. The researchers found a half-metre-long female with an egg inside of her. It too had the same distinctive ridges. After nearly 40 years, the shark species that had laid the Rowley Shoals eggs had been found.

Between the distinctive egg cases, physical features of the shark and differences in the shark鈥檚 DNA when compared with other demon catsharks, the researchers determined it was indeed a new species. They named it Apristurus听辞惫颈肠辞谤谤耻驳补迟耻蝉, with the species name referencing the 鈥渃orrugated鈥� surface of the egg case.

Most demon catsharks look alike, but this species has a shiny, white iris in its eyes, something it only shares with Apristurus听苍补办补测补颈, a species from New Caledonia and Papua New Guinea.

It is unknown what the eggs鈥� T-shaped ridges are for, says White. But he and his colleagues have ideas.

鈥淚t could be something to do with hydrodynamics, preventing [the eggs] getting washed away if currents are strong,鈥� he says. Other hypotheses include armour against predators, or keeping invertebrates from growing on the eggs and asphyxiating the embryos inside.

at San Jos茅 State University in California says the findings highlight that there is 鈥渙bviously a lot out there still to be discovered, especially when it comes to sharks and rays鈥�.

White notes that this Australian demon catshark isn鈥檛 the first shark or ray to be discovered via its egg. An Antarctic skate was described solely on its egg case in 1904. It wasn鈥檛 that the skate itself was discovered.

Researchers are still describing many new shark and ray species. Ebert and a colleague described a new Apristurus species from the Indian Ocean in 2021.

鈥淎lmost 20 per cent of the species we know have been discovered within the last 15 to 20 years,鈥� he says.