52 | ULTRAMARINE Twinkle, Twinkle, Little Star

By Tony Wu Digital illustration ©Christopher Hart

he brittlestar is a humble animal. It animal’s arms is a single calcite crystal, friend, who after hearing about some of Thas no head, a disk-shaped body, and and each “window” is in the shape of a the vexing issues facing the ocean, said, five long-thin “brittle” arms that it uses double lens... Interesting. “It’s quite sad, but one person can’t make for locomotion. An echinoderm, the brit- a difference.” We talked about this for tlestar is closely related to other familiar Curiosity peaked, they exposed some some time, and I brought up examples reef crawlers like starfish, urchins and of the crystals to light, and found that of individuals I know who have made sea cucumbers. Most divers have prob- the clear, window-like areas are able important contributions to changing the ably come across brittlestars; very few to direct and focus light. Even more world around us. (including me) pay much attention to exciting, the researchers meticulously them. measured the optimal focal distance for Then echinoderms came to mind, these miniature lenses, and found that it specifically Ophiocoma wendtii. But there’s more here than meets the corresponds precisely with the depth at eye. which nerve bundles are located beneath In the case of this animal, it’s reason- each of the lenses in the brittlestar’s able to conclude that just one lens A few years ago, a group of research- arms. Finally, the quality of the lens im- wouldn’t make much of difference. After ers published a study about a particular ages is such that some researchers believe all, the small lenses can only point in one brittlestar – Ophiocoma wendtii – a species the lens construction to be superior to direction at a time, with a very limited that ranges from Bermuda to Brazil and manmade lenses. field of view. Predators and such are grows to about the size of an outstreched rarely so kind as to approach from the adult hand. If we put two and two together, it side where you just happen to be looking. appears very likely that the unassuming At first blush, there’s nothing par- brittlestar uses a complex network of For O. wendtii, it’s the collective result ticularly special about this brittlestar. lenses to process images from its sur- of hundreds, perhaps thousands, of indi- It’s brittle, it lives on the reef, it looks roundings. Being small, each individual vidual lenses that give it an advantage in awkward and alien. lens is probably not terribly effective. the quest for survival. Individual lenses But if all the lenses, which are distrib- do make a difference, but much more so Gordon Hendler, a marine biologist uted over the animals arms, are linked when other lenses are also functioning at the Natural History Museum of Los through the nervous system, what results and cooperating. Angeles County, noticed that O. wendtii is an elegant compound eye that imparts changes color from dark red during the vision to the brittlestar, and enables it to In many ways, we are like the lenses of day, to a black/ grey at night. This ap- change colours, detect predators and seek the brittlestar. Each of us can contribute parently trivial talent, of course, implies refuge. a lot of valuable information and effort to that the brittlestar can sense light, which preserving the environment, but we can would be extremely difficult for an Makes you think, doesn’t it? A simple be much more effective sharing what we animal without any obvious eyes or other animal, relatively low on the evolution- know, and cooperating with others. photoreceptors. ary ladder, may have one of the most complex, and effective photoreceptive/ So the next time that you come across Hendler and other researchers then vision systems in the animal kingdom. something (good or bad) that affects our noticed that among the many bumps reefs and waters, let others know. Write, and markings on the arms of the brit- Which brings me to the reason I started email, fax…whatever. tlestar were what appeared to be tiny, thinking about this. clear “windows”. With further work, The more lenses we have, the better they found that each of the bones in the At dinner recently, I met a friend of a we’ll be able to see.

August/September 07 | 53