​刺胞动物：美丽与毒素并存 Cnidaria: in A Human View

刺胞动物门（Cnidaria）是一类具有刺细胞的动物，因此又称为“刺丝（细）胞动物门”。早期刺胞动物与栉水母动物一起分为腔肠动物门（Coelenterata），但随着栉水母动物的单独分类，现在所说的“腔肠动物”通常指的是刺胞动物门的动物。

Cnidarians are a type of animal that have stinging cells and are therefore also known as "stinging-thread (cell) animals" in Chinese. In the past, cnidarians were grouped together with comb jellies in the Coelenterata phylum. However, with the separate of comb jellies, the term "coelenterate" now usually refers to animals in the Cnidaria phylum.

虽然大部分的刺胞动物生活在海水中，但是也有少部分生活在淡水中，其中最著名的便是“桃花水母”。这种淡水水母是目前我国唯一的淡水水母，而且在古代曾广泛分布。

Although most cnidarians live in seawater, there are also a few that live in freshwater, with the most famous being the "Peach Blossom Jellyfish". This freshwater jellyfish is the only known freshwater jellyfish in China and was widely distributed in ancient times. 

古代的中国人曾经从“化生论”的角度认为桃花水母是桃花花瓣落水变化而来的，将其视为爱情的象征，并称其为“桃花鱼”。有趣的是，这种命名方式和西方人的“冻冻鱼”（Jelly-fish）不谋而合，说明世界各地人们对水母的感觉还是有相似之处的。由于生态环境的改变，现在桃花水母已经比较常见了。

Ancient Chinese people believed that the Peach Blossom Jellyfish was formed by the petals of peach flowers falling into the water, and viewed it as a symbol of love, calling it the "Peach Blossom Fish". Interestingly, this naming convention coincides with that of Westerners who call it the "Jellyfish", indicating that people around the world have similar feelings about jellyfish. Due to changes in the ecological environment, Peach Blossom Jellyfish are now relatively common.

辐射对称是一个通用的术语，在动物学上，它意味着一个动物身体沿中心轴可以有多个切面，将身体分成两个相等的部分。普通的多孔动物通常生理上不对称，但刺胞动物却有着固定的辐射对称形态。这种对称只有上下之分，而没有前后左右之分。这样的身体结构适合于没有特定运动方向的生活方式，比如固着或漂浮生活。

Radial symmetry is a universal term that, in zoology, means an animal's body can be divided into equal parts along a central axis. Common sponges are usually physiologically asymmetrical, but cnidarians have a fixed radial symmetrical shape. This symmetry only has an upper and lower division and no left or right or front and back division. This kind of body structure is suitable for a lifestyle without a specific direction of movement, such as being attached to a surface or drifting in water. 

你能想象一个没有前后左右之分的生物吗？

Can you imagine a creature with no left or right or front and back division?

刺胞动物可谓是进化史上最早具有细胞外消化的动物之一。它们的体内有一个原始的、被体壁包裹的消化循环腔，通过分泌消化液对食物进行消化。在消化过程中，腔内水的流动不仅能将消化后的营养物质输送到身体各部分，还兼具循环的作用。但刺胞动物可没肛门，消化后的残渣都是通过唯一的口排出体外。

The world of cnidarians is truly fascinating! These creatures are some of the earliest animals to have evolved the ability to digest food outside their body. They have a primitive digestive cavity enclosed by their body wall, where they secrete digestive enzymes to break down their food. As the nutrients are absorbed, water flowing in the cavity helps circulate them throughout the body. However, cnidarians do not have an anus, so any undigested waste is expelled through their only opening, the mouth.

水螅则是主要由干细胞组成，极少出现完全分化的细胞，因此成为科研实验的宠儿。这么厉害的小家伙，还是值得好好研究一下的！

Unlike other cnidarians, hydra are mostly made up of stem cells that rarely differentiate into specialized cells, making them a favorite subject for scientific research. It's amazing to think that these tiny creatures, without any complex organs, can still teach us so much about biology!

水母的毒性是众所周知的，现在水母爆发的频率越来越高，这使得人们更加担心。事实上，海龟和翻车鱼是水母的天敌，近期水母的爆发与它们的减少有关。目前最出名和致命的剧毒水母可能是澳大利亚箱形水母，旧称“钟型水母”，俗称海黄蜂，生活在澳大利亚和新几内亚北部、菲律宾和越南。它们已经造成了无数人受伤或死亡事件。

Jellyfish are known for their venomous stings, and their increasing frequency of outbreaks is a growing concern. Interestingly, sea turtles and sunfish are natural predators of jellyfish, and the recent increase in jellyfish outbreaks may be due to a decrease in their population. The most famous and deadly jellyfish is probably the Australian box jellyfish (Chironex fleckeri), formerly known as the "sea wasp," which lives in northern Australia, Papua New Guinea, the Philippines, and Vietnam. They have caused countless injuries and deaths.

水母群体中，海蜇或许是最为知名、却不致命的物种。和其他水母一样，海蜇也经历了受精卵、囊胚、原肠胚、浮游幼虫、螅状幼体、横裂体、碟状体、成体等多个阶段。早在唐朝时，中国就已经开始食用海蜇了。

Jellyfish are perhaps the most well-known and non-lethal species among jellyfish populations. Like other jellyfish, they go through various stages such as fertilized eggs, embryos, blastulae, larvae, polyps, medusae, and adults. In fact, the Chinese have been eating jellyfish since the Tang Dynasty, which dates back to over a thousand years ago! 

珊瑚是一种只有水螅体的刺胞动物，它们在海底可以分泌出美丽的石灰骨骼，构成了浅海中特有的奇妙风景。这些珊瑚和藻类有共生关系，藻类需要珊瑚提供庇护，而珊瑚则能从藻类中获得养分和氧气。

Coral is a fascinating and unique animal that only has polyps, which are small tentacle-like structures, as its body parts. They can secrete beautiful calcium carbonate skeletons that make up the amazing scenery found in shallow seas. Coral has a symbiotic relationship with algae, where the algae need coral for shelter and in return, the coral gets nutrients and oxygen from the algae.

因为珊瑚的美丽和神秘，很多人都认为它们是植物。然而，珊瑚是一种动物，而且它们的再生能力并不像植物那么强。过度的人为采集和破坏，再加上气候变化的影响，导致珊瑚种群大量消失。目前，珊瑚已经被列为保护动物，需要得到更多的保护和关注。

Many people mistake coral for a plant due to its beauty and mystique. However, coral is an animal and its ability to regenerate is not as strong as that of a plant. Human activities such as overfishing and destruction, coupled with the effects of climate change, have resulted in the significant loss of coral populations. Coral is now listed as a protected animal, requiring more attention and protection to help them survive.

珊瑚不仅是美丽的海洋生物，依旧是一种刺胞动物。在热带海域中，许多珊瑚触手上有毒的刺胞对人体也有作用，可以用作珊瑚的自我防御和攻击其他生物的武器。

Coral reefs are not just beautiful ocean creatures, but also a type of stinging animals known as cnidarians. In tropical waters, many corals have toxic stinging cells on their tentacles that can affect humans, serving as a defense mechanism against predators or as a weapon to attack other organisms. 

但是，如果游客在海中接触珊瑚，就有可能被刺胞刺伤，导致刺胞皮炎。这种情况下，轻者会感到瘙痒和红斑，重者会出现红肿，剧烈的刺痒和疼痛，甚至过敏反应。因此，了解珊瑚的特性和注意保护自己是非常重要的。

However, if tourists come into contact with corals in the water, they may be stung by the cells, leading to a condition known as "coral dermatitis". In mild cases, there may be itching and redness, while severe cases can cause swelling, intense itching and pain, and even allergic reactions. Therefore, it is important to understand the characteristics of corals and take measures to protect oneself while enjoying the beauty of the ocean.

了解刺胞动物是非常重要的，因为它们是海洋生态系统中的重要组成部分。珊瑚和水母都属于刺胞动物，它们对海洋生态系统起着重要的作用。了解刺胞动物的生态特点和生活习性可以帮助我们更好地保护海洋生态系统，减少人为干扰和破坏。

It's important to understand Cnidarians because they play a significant role in marine ecosystems. Coral and jellyfish are both examples of Cnidarians, and they have important ecological roles. Understanding the ecological characteristics and habits of Cnidarians can help us protect marine ecosystems from human interference and destruction.

此外，刺胞动物中的一些物种，如水母的触手上含有毒刺胞，对人类也有影响。了解这些动物可以帮助我们更好地预防和应对相关的健康问题。

Moreover, some Cnidarian species, such as jellyfish, have stinging cells on their tentacles that can affect humans. Understanding these animals can help us better prevent and deal with related health issues.

综上所述，了解刺胞动物不仅有助于保护海洋生态系统，还可以提高我们对自然界的认识和理解。让我们一起学习动物学，认识身边的动物吧。

In summary, learning about Cnidarians not only helps protect marine ecosystems, but also increases our knowledge and understanding of the natural world. Let's learn about animals and gain a better understanding of them!