海膽沒有眼鏡，拿什么來看世界？

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.

海膽是人類已知的唯一一種不需要眼睛就能看清物體的動物。瑞典隆德大學(xué)的研究人員們近期在一項研究中證實了這一點，他們發(fā)現(xiàn)這種多刺的球形動物視覺分辨率較低。

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.

海膽存在于全球溫暖的海底，在寒冷的極地區(qū)域十分罕見。海膽常常生活在深海里，它們在珊瑚礁中也很常見。人們對它們不甚喜愛，因為海膽會蜇人。

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為了他的博士論文進行了這一研究。他與同事專注研究名為Diadema africanum的海膽，他們將海膽放在了墻壁上有各種陰影區(qū)域的圓缸中，同時對其照射強光。

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.

先前的研究發(fā)現(xiàn)雖然海膽沒有眼睛，但它們能夠通過觸手一樣的腳視物。該研究進一步證實了這一點。

“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解釋道：“一般而言，海膽會走到陰影區(qū)域?qū)で蟊幼o。我注意到它們對特定大小的圖片有反應(yīng)，于是對它們的視力進行了測量。”

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的研究結(jié)果表明，海膽那像管子一樣的腳上含有光敏感細胞，而它們的腳遍布全身。這讓它們成為了動物王國中獨一無二的存在。

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

Kirwan說道：“你可以將一整只海膽看成一個復(fù)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及其同事在另外一個研究中，拿一個快速移動的輪廓模擬捕食者靠近海膽的場景。接著他記錄了輪廓必須有多大，海膽才能有所反應(yīng)。

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.

根據(jù)他的計算，一個物體必須在海膽三百六十度的視角中占據(jù)30至70度，才能讓海膽看見。人類的視力更加精確，物品只需要占據(jù)0.02度就能被看見。這進一步證實海膽的視力很低。

“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總結(jié)道：“然而，這依舊能夠滿足海膽的需求。畢竟對于一個沒有眼睛的動物來說，能夠看見世界已經(jīng)很幸運。”

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，海膽的腳還能夠幫助它們進食和移動。某些種類的海膽還能夠利用腳來附著在其它物體表面，方便它們在栽跟頭時糾正位置。