Cloze: Stingers of the Sea 海中“刺”客 ── 水母

Given impressive-sounding names like "Portuguese man-of-war," jellyfish are certainly respected and feared by humans. Not exactly a fish, and lacking a spine, this creature has a single body cavity or mouth. Any food consumed passes through this opening, and so do undigested remains being expelled.

A jellyfish's tentacles, which can exceed 30 meters in length, drag through the sea and capture any prey that may be in their path. Special cells that line the tentacles then fire small "arrows" into the victim, paralyzing it with a poison toxic enough to freeze even a human. The unfortunate prey is then drawn into the jellyfish's mouth.

Possessing neither blood nor brain, jellyfish are primarily filled with a jelly-like substance loaded with nerve cells that help them navigate the seas. These cells detect light and touch, and then pass this information on to muscle cells.

In all its simplicity, the jellyfish has existed for more than 600 million years with little change. Perhaps the jellyfish is indeed nature's perfect beast.

擁有“葡萄牙軍艦”這個聽起來就讓人印象深刻的名字，水母的確讓人類又敬又怕。這種生物既非魚類，又缺少脊椎，它只有一個體腔，或者也可稱之為嘴巴。任何被攝取的食物都要經過這個開口，沒有被消化的殘骸也是由此排出。

水母在海中拖曳著長度可以超過30米的觸須，捕捉任何可能在它前進路線上的獵物。水母的觸須上遍布著一種特殊的細胞，它可以向受害者射出“小箭”，足以讓一個人動彈不得的毒液去麻痹它。接著這不幸的獵物就被吸入水母的嘴里。

水母既沒有血液也沒有大腦，主要由滿是膠狀物質的神經細胞來協助它在海中的航行。這些細胞能偵測光線和觸覺，然后把信息傳達到肌肉細胞。

雖然水母的結構很簡單，它已經在地球上存在超過六億年了，而且沒有什么改變。也許水母真的是自然界中真正的霸主。