Sea cucumbers aren't all boring, trundling bags. Some of them swim -- and glow. Though I opted to focus on creatures found at greater depths in my last post, one of the creatures observed by the Deepsea Challenger expedition in the New Britain Trench at a relatively shallow 1000 meters was just such a swimming sea cucumber. The graceful, languid flapping of these creatures can be hypnotic.

Before I narrowed the focus of my post, I decided to try and find some video of this beautiful swimming to share with you, and lo, I stumbled on a film that contained that and a lot more. Since I couldn't fit it in last time, I decided it deserved its own post.

You've probably picked up on my fascination with biologist Edith Widder's work with bioluminescence. She tells the story of sea creatures that cover themselves with sticky glowing packets that come off on attackers to alert the attacker's predators, a tactic she has compared to the exploding paint packs deposited in bags of pilfered cash for bank robbers. The following sea cucumber video seems to illustrate that tale.

In it, you first see the swimming sea cucumber in natural light doing the dance I wanted to show you, and then glowing in the dark. Then, you can see someone's hand caress the sea cucumber. Then, when the lights go out, you can see the glowing packets stuck to the hand by the cucumber flying off like fireflies.

Pretty cool, huh?

I believe this video may be the product of the Widder lab, since ORCA -- the Ocean Research and Conservation Association -- is a group she founded.

I also recently stumbled on a follow-up to the original 2010 Edith Widder TED talk that I've posted here numerous times before. In the following 2011 sequel, she gives many other fascinating examples of the bioluminescent burglar alarm phenomenon displayed in the sea cucumber above. She also does a super-cool live demo of the glow of bioluminescent dinoflagellates when agitated. Nocturnal beachgoers sometimes spot this eerie phenomenon when plunging waves stimulate plankton to glow.

In my last post, someone asked why the sea cucumbers of Challenger Deep would be so expertly camouflaged in a place that is presumably black as pitch. Deep sea predators with headlights could be one answer -- even if the cucumber originally evolved to evade headlights at much shallower and more dangerous depths than the relatively predator-free bottom of the Mariana. This is, of course, sheer speculation on my part.

Finally, while researching this post I discovered Widder spoke at TED again just this February to explain how her team found and filmed the first giant squid in their own habitat, a topic I wrote about here a few months ago. It's worth watching this just to hear her tell the story in her own words, but she also expands much more eloquently on ideas I touched on here last time: if a two-story squid could elude us until now, surely many great biological discoveries await us in the deep ocean. But she also suggests there are other important reasons for prioritizing ocean exploration beyond the simple, if profound, joy of discovery. Enjoy.