The new species Colobothrix deckeri is in the millipede family Dalodesmidae. It is remarkable because it is the first in its moisture-loving family to be found in a part of Australia with a low annual rainfall, between 400 and 500 mm.

The new species is also unusual for the shape of its sphaerotrichomes, which are tiny ball-shaped structures found on the legs of mature males in Dalodesmidae and some other millipedes. Sphaerotrichomes normally have a long, pointed seta emerging from the ball. The new species has been placed in the new genus Colobothrix, which means “stunted hair”, because the seta on its sphaerotrichomes is reduced to a short, blunt rod.

Colobothrix deckeri was named by Australian myriapodologist Robert Mesibov in honour of German colleague Peter Decker, who played a key role in the story behind the species rediscovery, as described in the peer-reviewed, open-access journal ZooKeys.

The first specimen of C. deckeri was collected in 1936 and deposited as an unidentified millipede in the South Australian Museum (SAMA). In 2015 Decker found the specimen among many he borrowed from the Museum for his PhD work on another millipede family, Paradoxosomatidae.

Decker recognised the specimen as a dalodesmid and sent images of its microscopic characters to Mesibov, who is a dalodesmid specialist. The specimen was the first evidence for Dalodesmidae in dry South Australia, and in 2016 and 2017 Mesibov searched the 1936 locality on South Australia's lower Yorke Peninsula for fresh material. Both searches were unsuccessful, although the two trips yielded a new paradoxosomatid.

Meanwhile, arachnologists Michael Rix and Danilo Harms had been sampling spiders and associated litter invertebrates on Kangaroo Island, South Australia, about 50 km south of the 1936 locality. In 2010 they discovered a remarkable new species of assassin spider from a single site in the relatively wet northwestern corner of the island. They also collected several specimens of the new, still unidentified millipede at the same site and deposited them in the Western Australian Museum (WAM).

Early this year, Mesibov found the WAM millipede record online. He emailed WAM curator Mark Harvey, who kindly provided several images of the millipede collected by Rix and Harms, with close-ups of its diagnostic characters. The images showed that the 2010 Kangaroo Island specimens were the same species that had been collected in 1936 on the Yorke Peninsula.

Kangaroo Island suffered devastating bushfires in 2020. It was feared that the new assassin spider had been pushed towards extinction by the fires, because the 2010 site had been burned out. In 2021, arachnologist Jessica Marsh searched for the new assassin spider on Kangaroo Island. She found more specimens in 2021 at sites several kilometers distant from the 2010 site, and her by-catch included the new millipede.

“Third time lucky!” said Mesibov. “I found the new millipede alive and well this year at relatively wet sites not far from its 2010 and 2021 localities.” He collected a few specimens for description and future genetic analysis, and the 1936, 2021 and 2026 specimens are now all housed in SAMA.

An unanswered question is whether C. deckeri still lives on South Australia’s Yorke Peninsula, which is much drier than northwestern Kangaroo Island.

“The 1936 locality is underlain by limestone,” said Mesibov, “and the rock is broken where it is exposed at the ground surface. I wonder if the species survives in small voids in this bedrock, as a relict from wetter periods in South Australia’s past. That might explain why I couldn’t find it in 2016 and 2017, and how it could persist in such a dry climate.”

Mesibov R (2026) Two new millipede genera and species from Kangaroo Island, South Australia (Polydesmida, Dalodesmidae, Spirostreptida, Cambalidae). ZooKeys 1295: 277-291. https://doi.org/10.3897/zookeys.1295.214938