國家地理:水母為何如此迷人(2)

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Scary, squishy, cool, brainless, mesmerizing -- jellyfish are all of these and a whole lot more. Anatomically they're relatively simple animals; they lack not just brains, but also blood and bones, and possess only rudimentary sense organs. Despite their name, jellyfish aren't, of course, fish. In fact they aren't any one thing.

可怕、黏糊、酷炫、無腦、迷人--水母綜合了所有這些特點(diǎn)，而且遠(yuǎn)不只如此。從身體構(gòu)造來看，它們是相對簡單的動物；它們不只沒有腦，也沒有血液和骨骼，只有基本的感覺器官。水母的英文是jellyfish，盡管如此，它們并不是魚。事實(shí)上，水母在分類學(xué)上無法分類成單一群體。

Many of the creatures lumped together as jellyfish are no more closely related than, say, horseflies are to horses. Not only do they occupy disparate branches of the animal family tree, but they also live in different habitats; some like the ocean surface, others the depths, and a few prefer freshwater. What unites them is that they've converged on a similarly successful strategy for floating through life: Their bodies are gelatinous.

許多被籠統(tǒng)歸類成水母的動物，它們之間的親緣關(guān)系其實(shí)就跟馬蠅和馬一樣，并不密切。它們不但在動物系譜樹里占據(jù)不同的分支，也生活在不同的棲地里：有些喜歡海洋表面，有些喜歡深海，少數(shù)偏好淡水。這些動物的共同點(diǎn)，是它們都趨同演化出類似且成功的漂浮式生命策略：它們都有膠質(zhì)狀的身體。

Not surprisingly, given their diverse evolutionary history, jellies exhibit a fantastic range of shapes, sizes, and behaviors. When it comes to reproduction, they're some of the most versatile creatures on the planet. Jellyfish can produce offspring both sexually and asexually; depending on the species, they may be able to create copies of themselves by dividing in two, or laying down little pods of cells, or spinning off tiny snowflake-shaped clones in a process known as strobilation. Most astonishing of all, some jellies seem able to reproduce from beyond the grave.

可以想見，由于水母的演化史各異，它們也呈現(xiàn)出形形色色的外形、大小和行為。在繁殖方面，它們可以說是地球上最多才多藝的生物。水母可以行有性生殖與無性生殖；按物種不同，有的可以一分為二變出另外一個自己、有的會在水里產(chǎn)下精子或卵子，有的能透過稱為斷裂生殖的過程，釋放出許多微小的、雪花狀的無性繁殖系。最令人驚訝的是，有些水母似乎在死后還可以繁殖。

The so-called immortal jellyfish resembles a tiny, hairy thimble and lives in the Mediterranean Sea and also off Japan. Members of the species can reverse the aging process so that instead of expiring, they reconstitute themselves as juveniles. The juvenile then starts the jellyfish's life cycle all over again. It's as if a frog, say, were to revert to a tadpole or a butterfly to a caterpillar. Scientists call the near-miraculous process transdifferentiation.

有永生水母之稱的燈塔水母，看起來就像是毛茸茸的迷你頂針，生活在地中海與日本沿海。這種水母可以逆轉(zhuǎn)老化過程，因此不會死亡，反而能返老還童，回到幼體期，重新開始生命周期。這就好比一只青蛙重新變成蝌蚪，或是蝴蝶重新回到毛毛蟲的階段?？茖W(xué)家將這種堪稱奇跡的過程稱為轉(zhuǎn)分化。