Water spider spins its own scuba tank

[Sledge]

From the description though it sounds more like an artificial gill.

http://news.nationalgeographic.com/news/2007/08/070828-scuba-spider.html

Scientists at the University of Bern, Switzerland, determined that spiders use these scuba tanks, called air bells, as reservoirs, monitoring and replenishing oxygen levels to enable the animals to live underwater.

"The water spider's air bell is in some ways working like an external lung," said study co-author Michael Taborsky.


...

As the spider fills the web structure with air, the structure takes on a bell shape and a silvery sheen. The silk membrane allows oxygen to diffuse in from the water and carbon dioxide to diffuse out, so the spiders do not have to replenish the air supply often.

 

[BidAndDive.com]

Hey now, that's pretty nifty...I wonder how much refills cost?

 

[archman]

More cool excerpts from the article. I would love to see how the scientists did the air experiments.
http://news.nationalgeographic.com/news/2007/08/070828-scuba-spider_2.html

The team replaced the gas volume in each spider's air bell with pure oxygen, pure carbon dioxide, or a control of ambient air to test whether the spiders keep tabs on the air quality in the bells.

The team speculated that if the arachnids rely on air bells as a source of oxygen, their ability to detect elevated amounts of carbon dioxide and restore a proper balance is critical.

The test spiders only reacted to the carbon dioxide treatment, surfacing more frequently and increasing bell-building behavior until oxygen levels had been sufficiently replenished, co-author Taborksy said.