刺胞动物：水螅、水母，基本特征 Cnidaria: Hydroids, Jellyfishes

朋友们，刺胞动物曾经和栉水母动物一起组成了腔肠动物门。但是，最近的系统发生学研究表明刺胞动物其实是一个单系群。

Did you know that cnidarians were once classified with ctenophores as part of the phylum Coelenterata? However, recent studies show that cnidarians actually form a monophyletic group!

经典的动物学把刺胞动物分为三个纲，分别是水螅纲、钵水母纲和珊瑚纲。但是现代部分分类学研究也主张把它们分为珊瑚纲、立方水母纲、水螅纲、水螅虫纲、钵水母纲和十字水母纲，还有一个独立于以上阶元的黏体动物类群。

Traditional taxonomy divides cnidarians into three classes: Hydrozoa, Scyphozoa, and Anthozoa. But modern classification divides them into Anthozoa, Cubozoa, Hydrozoa, Staurozoa, Scyphozoa, and a separate group called Myxozoa.

虽然这些纲下阶元已经比较稳定，但是为了符合我们的生产生活实践和现阶段的研究生入学考试要求，本系列还是会按照经典类群来为大家介绍！

Although the current taxonomic levels are relatively stable, we will STILL use the traditional classification system to introduce cnidarians, to better understand our daily life and meet the requirements of certain traditional exams. 

首先我们要聊聊一个神奇的动物——薮枝螅，也叫薮枝虫。它是水螅群体生活的代表呢，薮枝螅的群体长成树状，可以固着在岩石和海藻上，大小不一，有的只有几厘米，有的却可以长到十几厘米。

Let's talk about a magical creature - the Obelia  hydrozoans, also known as the "sea fur". It's a representative of colonial hydroid animals! The colonies of hydroids grow in a tree-like shape and can attach to rocks and seaweed, ranging in size from a few centimeters to over ten centimeters.

薮枝螅的基部固着的部分叫做螅根，螅根向上长出螅茎，螅茎分支末端有两种形态的螅体。一种是有口有触手的水螅形，另一种是无口无触手的棒状繁殖型螅体。

The base of the hydroid polyp is called the hydrorhiza, which grows upward to form the hydrocaulus. The hydrocaulus branches and ends with two types of hydroid bodies: the polyp with mouth and tentacles, and the non-feeding reproductive body.

薮枝虫的水母体是雌雄异体，通过性生殖产生水母芽。薮枝虫卵在水中受精，发育成表面具有纤毛、自由游泳的浮浪幼虫，经过一段时间后固着下来，以出芽方式形成新的群体。

The medusa is dioecious, and it produces medusae buds through sexual reproduction. The hydroid eggs are fertilized in the water and develop into free-swimming, ciliated larvae. After a period of time, they settle and form new colonies by budding.

除了薮枝螅，水螅纲还有其他一些种类，比如筒螅，但只有水螅型，没有水母型。还有一些种类水母型发达，水螅型不发达，比如钩手水母（Gonionemus vertens）、桃花水母（Craspedacusta）。这些神奇的生物是不是很吸引人呢？

Besides the hydroid, there are other types of hydrozoans in the class Hydrozoa, such as Tubularia, which only have the polyp form and no medusa form. There are also species where the medusa form is well-developed, but the polyp form is not, such as the Gonionemus vertens and the Craspedacusta. Aren't these magical creatures fascinating?

钵水母类动物，是一类体型较大的海洋生物，它们的水母型十分发达。其中，海月水母是最典型的代表，通常呈现盘状，透明或近乎白色，边缘有触手。在经典动物学研究中，人们认为它们主要以漂浮为生。

Let's talk about a fascinating group of marine animals called Scyphozoa. These animals are quite large and have a well-developed jellyfish body shape. One of the most typical representatives of this group is the Moon Jellyfish (Aurelia aurita，英文确实如此). It's usually flat and transparent or almost white with tentacles along the edge. In classical zoology, people believed that they mainly live by floating foraging.

海月水母的伞体边缘还有8个缺口，内有触手囊，这些囊不仅能够感受到味道和嗅觉，还能维持平衡。钵水母类动物是肉食性动物，海月水母的口位于伞体中央，呈四角形，四个角上各有一条口腕，可以过滤水中的小型浮游生物，并将食物送入口腔和胃中进行消化。

The umbrella edge of a moon jellyfish has eight notches with tentacle pouches inside. These pouches not only sense taste and smell but also help maintain balance. Bowl jellyfish are carnivorous, and the mouth of a moon jellyfish is located in the center of the umbrella, forming a square shape with four oral arms. They filter small planktonic organisms from the water and digest them in their oral cavity and stomach.

大家可能有所了解，水母的胃腔可以向四方扩大形成四个胃囊，胃囊间有分支或不分支的辐管相连，构成了水母复杂的消化系统。

Did you know that the stomach of a jellyfish can expand in all four directions, forming four gastric pouches? These pouches are connected by branching or unbranched radial canals, forming the complex digestive system of jellyfish. 

海月水母的胃囊内还有四个马蹄形的生殖腺，它们既是雌性又是雄性。有趣的是，雄性的精子会成熟后随水流进入雌性体内受精。有些钵水母还会在海水中直接受精。

There are also four horseshoe-shaped gonads in the stomach pouch of moon jellyfish, which are both male and female. Interestingly, the mature sperm of males will flow into the female's body and fertilize the eggs. Some bowl jellyfish even directly produce sperm and eggs in the seawater!

水母是一个神秘的海洋生物，拥有奇特的生命周期。它们的生命从受精卵开始，经历了一系列的变化才能成为美丽的水母。水母的生殖腺位于胃囊内部，经过受精卵发育成为螅状幼体，最后发育成为水母成体。

Jellyfish are mysterious creatures of the sea, with a unique life cycle. They start out as fertilized eggs and go through a series of changes before becoming beautiful jellyfish. Their reproductive organs are located in their stomachs, and after fertilized eggs develop into larvae, they eventually become the jellyfish that we see.

有些水母只有水母型，而有些则有水母型和水螅型世代交替，它们的生命可谓是奥妙无穷啊！

Some jellyfish only exist in the form of an adult jellyfish, while others go through generations of both jellyfish and larvae. The life cycle of jellyfish is truly mysterious!

有些钵水母类动物中胶层特别发达，这使得它们在经济上也有很高的价值。大家可能听说过海蜇（Rhopilema esculentum），它们的口腕经常愈合在一起。海蜇是一种人们喜闻乐见的海鲜，它的伞部和口柄部可以经过加工处理后分别制成海蜇皮和海蜇头，被广泛应用于餐饮业。

Some jellyfishes have a special layer called the mesoglea that is highly developed, making them valuable economically. You may have heard of the flame jellyfish (Rhopilema esculentum), also known as a species of Rootmouth Jellyfish. Their oral arms frequently stick together, but they are a popular seafood delicacy. The umbrella and the oral arms can be processed into jellyfish skin and jellyfish head, which are widely used in the food industry.

在这篇文章中，我们共同领略到了水螅和水母的多样性和神秘之处。水母是一个令人着迷的生物群体，包括了各种形态、大小和生活方式的成员。

In this article, we collectively appreciate the diversity and mystery of hydra and jellyfish. Jellyfish are a fascinating group of organisms, encompassing members of various shapes, sizes, and lifestyles. 

从优雅的海月水母到具有刺细胞的海蜇，它们都在海洋中展示着不同的生命之美。而水螅则以其简单而又神秘的生活方式，让我们对生命的多样性有了更深刻的认识。让我们继续探索这些神秘的生物，感受它们的美丽和神奇。

From the graceful moon jellyfish to the stinging sea jellies, they all showcase the beauty of different life forms in the ocean. Meanwhile, hydra, with its simple yet enigmatic lifestyle, deepens our understanding of life’s diversity. Let’s continue exploring these mysterious creatures and marvel at their beauty and wonder.