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.  

拥有“葡萄牙军舰”这个听起来就让人印象深刻的名字，水母的确让人类又敬又怕。这种生物既非鱼类，又缺少脊椎，它只有一个体腔，或者也可称之为嘴巴。任何被摄取的食物都要经过这个开口，没有被消化的残骸也是由此排出。

水母在海中拖曳着长度可以超过30米的触须，捕捉任何可能在它前进路线上的猎物。水母的触须上遍布着一种特殊的细胞，它可以向受害者射出“小箭”，足以让一个人动弹不得的毒液去麻痹它。接着这不幸的猎物就被吸入水母的嘴里。

水母既没有血液也没有大脑，主要由满是胶状物质的神经细胞来协助它在海中的航行。这些细胞能侦测光线和触觉，然后把信息传达到肌肉细胞。

虽然水母的结构很简单，它已经在地球上存在超过六亿年了，而且没有什么改变。也许水母真的是自然界中真正的霸主。