Extinct snail Chilonopsis melanoides – from the Atlantic to Aotearoa

Extinct snail Chilonopsis melanoides – from the Atlantic to Aotearoa

While rummaging through cabinets, Curator Invertebrates Rodrigo Salvador found a two-centimetre treasure: the shell of an extinct snail from Saint Helena. Here he talks about the ecology of Saint Helena and how the snail ended up in a museum in New Zealand.

You would be excused if youve never heard of Saint Helena before. It is a very small British island, roughly 120 km square, sitting 2,000 km away from the coast of Africa, right in the middle of the Atlantic.

Manati Bay, Saint Helena. Photo by Peter Neaum, CC BY 3.0, via Wikimedia Commons (dark borders removed)

Despite its small size, Saint Helena is tremendously important biodiversity-wise. So much so that the United Kingdom has put it on the list to become a UNESCO World Heritage Site. But what makes it so unique?

The island was formed by volcanic eruptions back in the Miocene Epoch, between 14 and 11 million years ago. Since then, a variety of environments developed there, from desert areas to highland forests. Saint Helena was an evolutionary playground during those millions of years and across that range of habitats, especially due to its isolation from other landmasses. Over 400 unique species of animals, plants, and fungi have evolved there.

But you know where this is going, right?

Colonial pile on

Saint Helena was discovered – and named – by the Portuguese in 1502. In the century that followed, the island was ravaged by the settlers, their domestic animals, pets, and uninvited guests (mice and rats). The Portuguese were eventually bullied off the island by the British, who piled up on the damage. Saint Helena was for a long time an important port of call in the East India route. Hundreds of ships stopped there every year.

Shipping off St. Helena, oil on canvas by Adam Callandar (late 18th to early 19th century). Public domain, via Wikimedia Commons

During that time, a great deal of the islands natural cover was lost and many species became extinct. We know about such species by the semi-fossilised remains theyve left behind, such as eroded bones and shells. And a few other species we know only from brief mentions in writings people left behind.

One of the high-profile casualties was the Saint Helena rail (Aphanocrex podarces). This flightless bird was about the size of New Zealands charismatic rail, the weka. Saint Helenas rail was extinct in the early 16th century, soon after the Portuguese arrived with their cats and rats. Out of the eight endemic bird species of Saint Helena, only one still remains, the wirebird (Charadrius sanctaehelenae) [PDF 1.5MB], which is even present in the territorys flag.

Sub-fossil skull of the Saint Helena rail, with the beak reconstructed based on other rails. Olson, Storrs L., Public domain, via Wikimedia Commons

Snails pace not fast enough

Another animal group that took a major hit was the land snails. This is not surprising, though. Land and freshwater snails, together with amphibians, are the animals most threatened by extinction.

Saint Helena had over 20 endemic snail species and a rather unique endemic genus: Chilonopsis. This genus belongs to the family Achatinidae, the same as the giant African snails, and contains eight species (or maybe nine, depending on whom you ask). All eight became extinct during the time since Portuguese arrival and the late 19th century.

Even though naturalists managed to collect some shells (and even one live specimen) and send them back to natural history collections, it is rather rare to come across one of them. So I was positively surprised to find one here at our collection in Te Papa.

Our specimen is a shell of Chilonopsis melanoides – and one in great condition. This is the most unusual species in the genus because of the shape of its shell: narrow and elongated. It was also likely the last Chilonopsis species to become extinct. Because examples of this species are hard to come across and photos of it are apparently non-existent online, I decided to share this small treasure here.

The shell of a Chilonopsis melanoides in three different views. Photo by Jean-Claude Stahl. Te Papa (M.209881)

The shell exchange

But how did this shell get to Te Papa? Well, it was once part of the collection of Henry Suter, a Swiss-born naturalist who migrated to New Zealand and studied snails. His amazing land snail collection included thousands of specimens from all around the world. Luckily, that collection was acquired by the then Dominion Museum and is now safely kept here at Te Papa.

Suter exchanged specimens with many naturalists worldwide and his Chilonopsis melanoides shell came from John Ponsonby, an English malacologist (a person who studies molluscs).

Even though Chilonopsis is now extinct, some of the Saint Helena endemic species still survive. That is the case of Succinea sanctaehelenae, known as the blushing snail because of the red marks on its “cheeks”. Blushing snails are widespread on the island, but their small population size makes them very close to being threatened.

By the same token, many of the non-snail endemic species of Saint Helena are vulnerable or endangered. The good news is that for the past three decades, there have been concerted efforts of reforestation and conservation on the island. So there is hope for them.

The past years, however, saw a drive to develop tourism in Saint Helena and concerns about potential impacts to the natural environment have been raised. The tourism industry was starting to pick up but was brutally cut short by the COVID-19 pandemic. Going forward, Saint Helena will have to regain its footing as a tourist destination while guarding its natural wonders.

Natural history of Saint Helena

If you want to know more about Saint Helena, the book St Helena and Ascension Island: A Natural History should be a good start. The website of the African Bird Club has plenty of information for birders, so its worth checking out.

Unfortunately, there’s nothing on that level for land snails; all we have are old and specialised scientific articles, some of which quite difficult to find.

And as a final note, another high-profile casualty on Saint Helena was Napoleon. He was exiled to the island in 1815 after his second abdication and died there in 1821. I know that was completely unrelated, but it is a rather curious tidbit: 2021 marks the bicentennial anniversary of his death.

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