An Ancient Snorkeler

Long before dinosaurs thundered across the land, before even the first fish dared to sprout fins, an unassuming yet extraordinary creature roamed the ancient seas. It was...

 

a snail.

 

Yochelcionella (yo-kel-see-oh-nell-uh) is a tiny, enigmatic mollusk from the Cambrian period, which ended about 485 million years ago. Its shell is adorned with a delightfully perplexing feature, a tubular snorkel-like extension near its peak. Paleontologists are debating its function. Was it an inhalant siphon drawing in fresh, oxygen-rich water? Or an exhalant tube expelling spent deoxygenated currents? Perhaps, in an elegant evolutionary flourish, it did both! No matter the answer, this humble creature is a key to the great puzzle of molluscan evolution.

  Yochelcionella greenlandica, stolen from Atkins & Peel, 2008.

The Cambrian was a period where evolution tried out a vast diversity of body plans. Imagine an ocean floor teeming with newly evolving life, an era of experimentation where nature sculpted forms wondrous and strange. In this grand evolutionary workshop, Yochelcionella thrived. Some of these ancient snails bore coiled shells with narrow openings, ideal for burrowing into sediment. In contrast, others stretched into almost straight, tube-like forms, better suited for crawling over the seafloor. Their varied designs suggest different lifestyles. Some snuggled into the ocean floor; others boldly roved above it. Yet all shared that curious snorkel, an evolutionary riddle awaiting a solution.

 

The fossil record whispers secrets of Yochelcionella’s long-lost world. Specimens have surfaced from the fossil beds of Greenland and North America, preserving glimpses of a vanished era. Recent discoveries in Greenland unveiled two new species, Yochelcionella greenlandica, and evidence points to its presence as far afield as New York and Quebec, and Yochelcionella gracilis, an elegant, almost straight-shelled form with a telltale fissure near its snorkel, a feature shared only by its distant cousin Y. fissurata. These scattered fossils paint a portrait of a creature that once spanned vast distances of the shallow Cambrian seas, a small but abundant player in the marine tapestry of its time.

 

Unlike its modern, sluggish relatives, Yochelcionella may have been a nimble navigator of the seabed, an explorer of the ocean’s frontier. Some species likely hugged the surface, while others partially buried themselves in sediment, siphoning water to keep oxygen flowing across their gills. If its snorkel functioned as a respiratory aid, it might have granted Yochelcionella an advantage in murky, low-oxygen waters, allowing it to filter cleaner currents from above, a periscope of sorts. 

In the grand evolutionary tree of mollusks, Yochelcionella belongs to the enigmatic Helcionelloida, an ancient lineage that may have paved the way for modern mollusks. Though lost to time, its distinctive snorkel speaks to an evolutionary experiment that never quite took hold in later molluscan lineages. Some scientists speculate it shares distant ties with today’s scaphopods, sleek, tubular tusk shells burrowing into the seafloor. Whether an ancestor or a relative on a different evolutionary path, Yochelcionella offers an intriguing glimpse into the incredible adaptability of early life.

 

Yochelcionella is likely more closely related to Neopilina (one of my obsessions) than to the rest of the gastropods, an early branching off of the mollusks, though this is challenging to determine because, well, Yochelcionella is extinct. 

 

Other ancient snails:

Pelagiella is another ancient fossil mollusk that resembles a snail; its shell is coiled. The equally ancient Helcionella, found in the famous Burgess Shale and other locations, is also considered closer to the snail branch of the evolutionary tree than Yochelcionella, it does not exhibit as distinct coiling as Pelagiella.

       Pelagiellacea fossil from Czechoslovakian shales (Horny, 1964).

        Helcionella, side view. (Ebbestad et al., 2024).

How did the evolutionary story of gastropods begin? That is still open for debate and research. The story of Yochelcionella with its snorkel-like appendage, remains a bit of an enigma and a testament to how natural selection’s experiments shape evolution. The adaptations that made it to modern times are a mix of luck and the right features under the right conditions. 

 

End note: the number of fossil mollusks described in 2023 is over 50. I had no idea there was that much activity in this field. 

 

 

Sources and Further Readings:

 

Atkins CJ, & Pee JS. 2004. New species of Yochelcionella (Mollusca: Helcionelloida) from the Lower Cambrian of North Greenland, Bulletin of the Geological Society of Denmark, vol. 51, pp. 1-9. Available at: https://doi.org/10.37570/bgsd-2004-51-01​.

 

Atkins CJ, & Peel JS. 2008. Yochelcionella (Mollusca, Helcionelloida) from the lower Cambrian of North America, Bulletin of Geosciences, vol. 83(1), pp. 23-38. Czech Geological Survey, Prague. Available at: https://www.researchgate.net/publication/26568981​.

 

Ebbestad JOR, Cederström P & Peel JS(2024) Helcionelloid molluscs from the lower Cambrian (Series 2, Stage 4) of southern Sweden, Historical Biology, 36:9, 1854-1882, DOI: 10.1080/08912963.2023.2234393

 

Gould SJ. 1989. Wonderful Life: The Burgess Shale and the Nature of History, W.W. Norton & Company.

 

Morris SC. 1998. The Crucible of Creation: The Burgess Shale and the Rise of Animals, Oxford University Press.