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Scientists Tour Elaborate, Deep-Sea ‘Snot Palaces’ for the First Time

Tiny transparent sea creatures make elaborate houses out of their own mucus. Now, researchers have illuminated the framework within these structures

The blue outlined tadpole-like creature at the center of this elaborate structure, made of mucus, is a giant larvacean. New techniques have allowed scientists to model and study this structure, which is used by the larvacean to gather food. (© 2002 MBARI)
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Small, transparent sea creatures called larvaceans build mansions out of mucus that house, protect and feed them, but these “snot palaces” are so delicate that scientists have found them hard to study. Now, researchers have used lasers mounted on an undersea robot to understand the architecture of the larvaceans’ gossamer homes, reports Seth Borenstein for the Associated Press.

The new study, published this week in the journal Nature, focuses on the giant larvaceans, which, despite their name, are only about five inches long. They look like see-through tadpoles with flat, beaver-style tails, and they hang in the ocean depths capturing floating bits of food in their houses. These creatures construct their dwellings at a tiny scale and inflate them to reach sizes of more than three feet across, which is equivalent to five-story buildings compared to the larvacean’s size, according to a statement.

“Think of a balloon that hasn't been blown up,” Kakani Katija, a bioengineer at Monterey Bay Aquarium Research Institute and first author of the new research, tells Hannah Seo of Popular Science of the structures before they’re inflated. The process is sort of similar to how a spider builds its web, but unlike with a spiderweb, these mucus houses are secreted all at once. Sadly, larvaceans don't have the appendage advantages that spiders have either.

“A spider has eight legs to build and lay down material for its web,” Katija tells Popular Science, “this animal really just has a head and a tail.”

Since the giant larvacean’s snotty digs are too fragile to study at the surface, researchers with the Monterey Bay Aquarium Research Institute (MBARI) used a 12,000-pound, remotely-operated vehicle equipped with scanning lasers to get a closer look, reports Rosanna Xia of the Los Angeles Times.

When the robot encountered a giant larvacean, the team used its sheet-like laser beam to illuminate the design of the mucus house by tracking the movements of particles through its various cavities, per the statement. The slices of the giant larvacean’s pad illuminated by the laser’s broad beam also provided the researchers with cross-sections of its internal structure. By combining these cross-sections the team created a 3D image of the transparent animal’s filtration system, much like a radiologist taking a CAT scan of the human body.

giant larvacean
This is a 3D reconstruction of a giant larvacean, revealing the complex structure of its inner filter. (© 2020 MBARI)

The researchers found these snot palaces have two layers: an amorphous outer bubble and a more structured, fist-sized inner sanctum made of two fluted chambers that the larvacean pumps water through by beating its tail. Both layers filter potential food particles from the water column, and are connected by a pair of inlet channels. The whole apparatus works to eventually deliver the choicest morsels to the larvacean’s mouth. With just the flaps of their tails, these tiny animals can filter more than 20 gallons of seawater per hour, according to the statement.

These gloopy home bodies construct their dwellings out of mucus secreted by cells on the tops of their heads and abandon them every day or so when they become too clogged with particles. Prior research has shown these parachute-like discards provide a crucial source of food for deep sea ecosystems, which also serves to sequester tons of carbon, combating climate change, according to the LA Times.

The new 3-D images of the giant larvacean’s house allowed marine biologists to “fly” through the chambers of the mucus abode using a virtual reality headset.

Learning how the larvaceans build their structures could help humans design better filters, lead to innovations in 3-D printing or even inspire NASA engineers, reports Yasemin Saplakoglu for Live Science.

“There are a lot of marine animals that use mucus to create really complex structures,” says Katija in the statement. “Now that we have a way to visualize them deep below the surface, we can finally understand how they function and what roles they play in the ocean.”

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