This Snail Experiences The Weirdest Form Of Metamorphosis You'll Ever Hear About

The deep-sea hydrothermal vent home of G. chessoia. Rogers et al.2012/Wikimedia Commons; CC BY 2.5

Robin Andrews 26 Jul 2018, 13:08

Metamorphosis (literally “change shape”) is biological magic. Particularly prominent in insects and amphibians, it describes the remarkable processes in which a sudden, widespread, physical, cellular change occurs post-birth or hatching, leading to the creation of what looks like, but certainly isn’t, an entirely new beast.

From dragonflies to salamanders, the process is never not breathtakingly bonkers, but as spotted by The New York Times, a species of snail might have all others beat. As elucidated by a Japan Agency for Marine-Earth Science and Technology-led team, Gigantopelta chessoia has perhaps the strangest form of metamorphosis you’re ever likely to hear about.

Now, this snail lives deep within the Southern and Indian Oceans, and it hangs around hydrothermal vents. At a glance, it’s nothing too special: it’s not too big, too small, and doesn’t have some freakish predatory behavior or an ingenious way to disguise or camouflage itself.

As with plenty of marine animals, it also has a two-step (biphasic) lifestyle. As the authors explain in the Proceedings of the Royal Society B, it begins as a small larval critter living in the water column of the open ocean, before undergoing a metamorphosis process, turning into a proper snail, and settling in for a life on or near the seabed as it grazes for dinner.

So far, so shrug. Careful observations by the team, including with the use of very tiny X-ray imaging equipment, revealed something far stranger happens after it’s been down there for a while.

“Post-settlement,” they explain, “the hydrothermal vent gastropod Gigantopelta chessoia experiences a further, cryptic metamorphosis.”

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Cryptic essentially means hidden, which points to the fact that this stage of metamorphosis doesn’t involve change on the outside of the animal, but the inside only. Unlike other creatures, this change is not related to sexual maturity either.

This is where it gets freaky.

At a certain size, the snail’s digestive tract ceases its proliferation; instead, a gland that acts as its food pipe – its esophagus – begins to expand dramatically. Based on 3D scans of the snails’ internal organs, it appears this change happens incredibly quickly too.

This new organ takes up most of the snail’s body space, whereupon bacteria rapidly move in and set up shop. The snail then has no further need for eating like all those other pathetic organisms around it, instead letting the bacteria do all the energy conversion it requires.

Hydrogen sulfide, which is in abundance at those hydrothermal vents, is used to create the energy. They spend the rest of their lives continuing to expand and, if they fancy it, reproduce – and the fact they no longer need to feed significantly shifts the energy balance of the entire ecosystem down there.

This isn’t the first time the unorthodox innards of G. chessoia have been peered into. A 2017 article led by Dr Chong Chen, who is also first author of the new study, generated some beautiful 3D imagery of the curious creature, along with another, similar snail found elsewhere.

Their conclusion back then zeroed in on not just the massive esophageal organ, but the fact that such animals – and perhaps plenty of others – are capable of extraordinary action: “rapidly and repeatedly evolving equivalent anatomical adaptations and close-knit relationships” with bacteria that use inorganic energy sources, like hydrogen sulfide, to live.

This new paper expands on the snail’s biology, and describes the world’s first discovery of cryptometamorphosis. The big question: does anything else do it?

Well, therein lies the rub: it’s difficult to see. Hopefully, this kicks off a new zoological hunt, where creatures thought to be capable of this are assessed with a brand-new set of eyes.

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