海胆没有眼镜，拿什么来看世界？

Sea urchins are the only animals that we know of that can see without having eyes. Researchers from Lund University, Sweden, recently confirmed this fact in a new study, showing that the spiny, globular animals have low-resolution-vision.

海胆是人类已知的唯一一种不需要眼睛就能看清物体的动物。瑞典隆德大学的研究人员们近期在一项研究中证实了这一点，他们发现这种多刺的球形动物视觉分辨率较低。

The sea urchin is found across warm ocean floors worldwide, but rarely in the colder, polar regions. Sea urchins are commonly found along the rocky ocean floor in both shallow and deeper water and sea urchins are also commonly found inhabiting coral reefs. People usually aren’t too fond of them, as coming into contact with sea urchins can result in an inadvertent sting.

海胆存在于全球温暖的海底，在寒冷的极地区域十分罕见。海胆常常生活在深海里，它们在珊瑚礁中也很常见。人们对它们不甚喜爱，因为海胆会蜇人。

John Kirwan conducted the research as part of his Ph.D. thesis. He and colleagues focused on a sea urchin species called Diadema africanum, which they placed in strongly illuminated cylinders that had various dark patches on the walls.

John Kirwan为了他的博士论文进行了这一研究。他与同事专注研究名为Diadema africanum的海胆，他们将海胆放在了墙壁上有各种阴影区域的圆缸中，同时对其照射强光。

Although they lack eyes, previous research had suggested that they can see through their tentacle-like tube feet. The experiment was designed to put this assumption to the test.

先前的研究发现虽然海胆没有眼睛，但它们能够通过触手一样的脚视物。该研究进一步证实了这一点。

“Ordinarily, sea urchins move towards dark areas in order to seek cover. When I notice that they react to certain sizes of images but not to others, I get a measurement of their visual acuity”, explained Kirwan.

Kirwan解释道：“一般而言，海胆会走到阴影区域寻求庇护。我注意到它们对特定大小的图片有反应，于是对它们的视力进行了测量。”

According to Kirwan, sea urchins have light-sensitive cells in their tube feet, which — like their famous spines — cover their whole body. This makes them unique in the animal kingdom.

Kirman的研究结果表明，海胆那像管子一样的脚上含有光敏感细胞，而它们的脚遍布全身。这让它们成为了动物王国中独一无二的存在。

“You could say that the entire sea urchin is one single compound eye,” Kirwan said.

Kirwan说道：“你可以将一整只海胆看成一个复合眼。”

In another experiment, Kirwan and colleagues introduced rapidly growing figures above the sea urchin, as a way of mimicking an approaching predator. He then recorded how large the figures had to be before the sea urchin reacted by pointing its spines towards the towering shadow.

Kirwan及其同事在另外一个研究中，拿一个快速移动的轮廓模拟捕食者靠近海胆的场景。接着他记录了轮廓必须有多大，海胆才能有所反应。

According to his calculations, an object must take between 30 and 70 degrees of the sea urchin’s surrounding 360-degree area in order for the animal to see it. Humans, who have much better visual acuity, need an object to take up only 0.02 degrees to detect it. This made it clear that the sea urchin has a very low-resolution vision — but it does indeed see.

根据他的计算，一个物体必须在海胆三百六十度的视角中占据30至70度，才能让海胆看见。人类的视力更加精确，物品只需要占据0.02度就能被看见。这进一步证实海胆的视力很低。

“However, this is still sufficient for the animal’s needs and behaviour. After all, it’s hardly poor eyesight for an animal with no eyes,” John Kirwan concludes.

John Kirwan总结道：“然而，这依旧能够满足海胆的需求。毕竟对于一个没有眼睛的动物来说，能够看见世界已经很幸运。”

Besides sensing light, the tube feet are used for feeding and locomotion. In some species, the tube feet also assist in attaching the sea urchin to surfaces or as levers to correct their position when they fall upside down.

除了感光外，海胆的脚还能够帮助它们进食和移动。某些种类的海胆还能够利用脚来附着在其它物体表面，方便它们在栽跟头时纠正位置。