Scott Trageser took pictures of several species of invertebrates he encountered on Hon Cau island, part of an archipelago off the southeast coast of Vietnam, and posted them on citizen science website iNaturalist, hoping that an expert somewhere in the world might be able to identify the specimens and benefit from his observations.

Then, in November 2015, that’s exactly what happened. Trageser was contacted by Junn Kitt Foon, a Malaysian malacologist who specializes in the snails of Southeast Asia.

Junn had identified one of the species captured on film by Trageser as Myxostoma petiverianum, a snail that had not been seen in over a hundred years. No photo of a live specimen had ever even been taken before.

Scientists have rediscovered a snail species not seen for over a hundred years after spotting a picture of the species on a citizen science website.

In 2014, Scott Trageser was working for the Biodiversity Group, an organization that works to encourage citizen science. He was stationed on Con Dao, an island that is part of an archipelago off the southeast coast of Vietnam, teaching secondary school students about how they could contribute to science without needing any formal training.

On August 3 of that year, Trageser took a day trip to a rarely visited satellite island of the archipelago called Hon Cau. Trageser himself is trained as a herpetologist, and thus had very little knowledge of the snail diversity on the islands.

But he was, of course, well aware of the power of citizen science. He took pictures of several species of invertebrates he encountered on Hon Cau and posted them on citizen science website iNaturalist, hoping that an expert somewhere in the world might be able to identify the specimens and benefit from Trageser’s observations.

Then, in November 2015, that’s exactly what happened. Trageser was contacted by Junn Kitt Foon, a Malaysian malacologist who specializes in the snails of Southeast Asia. Junn had identified one of the species captured on film by Trageser as Myxostoma petiverianum, a snail that had not been seen in over a hundred years. No photo of a live specimen had ever even been taken before.

Though the snail is common on Hon Cau, the island is so rarely visited due to national park restrictions and its distance from Con Son, the archipelago’s main island, that no researcher had ever traveled there to document the local flora and fauna.

“In lieu of academic researchers [being] present, citizen science is the next best thing,” Trageser told Mongabay.

Myxostoma petiverianum was first discovered during James Cook’s voyage in the South Seas in the 1700s, according to Junn. “The discovery was published by Thomas Martyn, in a famous hand-crafted book, The Universal Conchologist,” he told Mongabay, adding that the snail hasn’t been officially reported in scientific literature in over a century.*

The last time the species was documented was in 1905 by Dautzenberg and Fischer, a French scientific research team. Junn added that a checklist of land snails in Vietnam published in 2008 mentioned Myxostoma petiverianum, but nothing much was known about the species beyond that.

“I have been researching the genus Myxostoma since 2010,” Junn said. “Online information on the genus was almost non-existent back then. I have had a hard time looking for pictures of this genus online and had to look through 19th Century and early 20th century literature instead, which yielded a few hand-drawn illustrations of Myxostoma petiverianum.”

Junn says he was surprised and excited when he came across Trageser’s full-colour photo of a living snail while doing random searches for Southeast Asian land snail pictures on Google. “The photo back then was labelled simply as ‘Gastropods,’ with no mention of the species, but I knew instantly what it was. I was jumping around and shouting ecstatically, ‘That’s it! That’s the Myxostoma petiverianum I’ve been looking for!’

The species is safe and protected at the moment, being that its population lives within the Con Dao National Park, Junn said.

Though he has no plans to travel to the Con Dao archipelago and study the snail firsthand, Junn said he would “certainly” love to visit Hon Cau island with local malacologists if an opportunity arises in the future.

“Most importantly though,” he said, “I hope this rediscovery will inspire more scientists and citizen scientists to explore the diverse yet vastly understudied molluscs of Southeast Asia.”

*Correction 08/15/2016: Junn Kitt Foon would like to clarify that Myxostoma petiverianum has been rediscovered and reported by Egorov (2016) in an article in the journal Conchylia vol. 46, pages 97 to 102. However, the discovery of Myxostoma petiverianum on Hon Cau remains significant because it is a new distributional record for the species and it was made possible through citizen science.