轮虫动物（中）：精妙生理结构  Rotifera (Part 2/3): Internal Structures

轮虫的内部结构是如何排布的？它们微不足道的体积中究竟隐藏着哪些精密的生命结构？

How is the internal structure of rotifers designed? What precise life organizations are concealed within their minuscule volumes?

我们将简要地探讨这些问题，再次走进轮虫的微观王国。而当我们深入研究轮虫的繁殖策略时，将会发现它们是如何以奇妙的方式延续生命的，这将成为本文的重要探讨点。

How is the internal structure of rotifers designed? What precise life organizations are concealed within their minuscule volumes? We will systematically address these questions, guiding you into the microscopic kingdom of rotifers. As we delve into the study of their reproductive strategies, we will discover the fascinating ways in which they perpetuate life, serving as a focal point in this discussion.

在前文中，您了解了轮虫动物门的发现历史、演化、分类和基本特征。现在，让我们继续深入轮虫的神秘领域，揭示它们微小身体内部的精致结构和令人叹为观止的繁殖策略。

In the previous section, you learned about the discovery history, evolution, classification, and basic features of the phylum Rotifera. Now, let's continue our journey into the mysterious realm of rotifers, unveiling the intricate structures within their tiny bodies and the remarkable reproductive strategies that leave us in awe.

轮虫身体微小，因此它们并没有特化的循环和呼吸系统。相反，它们巧妙地通过身体表面直接进行气体交换和营养输送。这种简约而高效的生理机制使得轮虫能够在其微小的身体中实现必要的气体交换，同时也方便了养分的输送，为其在水中和湿地环境中的生存提供了巧妙的适应性。

Due to their minuscule size, rotifers lack specialized circulatory and respiratory systems. Instead, they ingeniously conduct gas exchange and nutrient transport directly through the surface of their bodies. This simple yet efficient physiological mechanism enables rotifers to achieve necessary gas exchange within their tiny bodies while facilitating the transport of nutrients. This clever adaptation contributes to their survival in aquatic and wetland environments.

轮虫的身体发育包括三个关键层次：外胚层、中胚层和内胚层。

Rotifer body development involves three crucial germ layers: the ectoderm, mesoderm, and endoderm.

1. 外胚层：外胚层形成了一薄层的角质外壳，通常被称为表皮或皮层（cuticle）。这一层的存在起到了保护作用，有效地防止轮虫受到外部环境的伤害。表皮上还有一些附属结构，如纤毛、刺和鳞片等，这些结构对于感知环境和防御敌人都发挥着重要的作用。

Ectoderm: The ectoderm forms a thin layer called the cuticle, commonly referred to as the epidermis or outer layer. This layer serves a protective function, effectively preventing rotifers from external environmental harm. The cuticle also features appendages such as cilia, spines, and scales, which play vital roles in environmental sensing and defense against predators.

2. 中胚层：中胚层形成了一层称为肌上皮层（myoepithelium）的肌肉层。这一层的存在使得轮虫能够进行运动，并在一定程度上实现身体的变形。肌上皮层的协同收缩和伸展为轮虫的运动提供了力量和柔韧性。

Mesoderm: The mesoderm forms a muscular layer known as the myoepithelium. This layer enables rotifers to move and achieve some degree of body deformation. The coordinated contraction and extension of the myoepithelium provide strength and flexibility for the movement of rotifers.

3. 内胚层：内胚层负责形成内部器官，其中包括消化系统、排泄系统和神经系统等。这些内部器官在维持生命活动和协调不同生理过程方面起到了关键的作用。

Endoderm: The endoderm is responsible for forming internal organs, including the digestive system, excretory system, and nervous system, among others. These internal organs play a crucial role in sustaining life processes and coordinating various physiological functions.

这三个胚层的协同发育为轮虫的整体结构和功能提供了坚实的基础。每一层在身体发育过程中扮演着独特而不可或缺的角色，使得轮虫在其微小的身体中具备了出色的生存和适应性。

The coordinated development of these three germ layers provides a solid foundation for the overall structure and function of rotifers. Each layer plays a unique and indispensable role in the process of body development, endowing rotifers with remarkable survival and adaptability within their tiny bodies.

轮虫的神经系统主要由一个脑神经节（brain ganglion）和一系列神经纤维组成。

The nervous system of a rotifer is primarily composed of a brain ganglion and a series of nerve fibers.

脑神经节位于头部环带的后方，是轮虫神经活动的中枢。它向上连接着眼点（eyespot），使轮虫能够感知光线的强弱和方向。在轮虫前方，通常还有触角（antenna）或头冠，这些结构能够感知触觉或化学刺激。脑神经节通过这些感知器官获取外部信息，为轮虫的行为和适应提供了重要的输入。

The brain ganglion is located behind the circlet in the head region and serves as the central hub for the nervous activities of the rotifer. It is connected upward to the eyespot, allowing the rotifer to perceive the intensity and direction of light. In the front of the rotifer, there are usually antennae or the corona, structures that can sense touch or chemical stimuli. The brain ganglion gathers external information through these sensory organs, providing crucial input for the rotifer's behavior and adaptation.

脑神经节向下连接一条腹神经索（ventral nerve cord），这条神经索贯穿整个身体，从头部延伸到尾部，分支至各个器官和肌肉层。这种布局使得神经信号能够有效地传递，协调轮虫身体的各个部分。腹神经索的支配范围包括内部器官和肌肉，通过这一系统，轮虫能够实现各种运动和生理功能。

The brain ganglion extends downward, connecting to a ventral nerve cord. This nerve cord traverses the entire body from the head to the tail, branching out to various organs and muscle layers. This arrangement facilitates the efficient transmission of nerve signals, coordinating different parts of the rotifer's body. The ventral nerve cord's jurisdiction includes internal organs and muscles, allowing the rotifer to perform various movements and physiological functions through this system.

轮虫的消化和排泄系统的复杂性和高效性使得它们能够在微小的身体中实现有效的食物处理和废物排除，为其在不同环境中的生存提供了重要的生理支持。

The complexity and efficiency of the rotifer's digestive and excretory systems enable them to efficiently process food and eliminate waste in their tiny bodies, providing crucial physiological support for their survival in different environments.

轮虫的消化系统包括口腔、咽喉、胃、肠和肛门。口位于头部环带的中央，具有张开和闭合的功能。咽是一个肌肉化的器官，内含一对硬质结构，称为颚器（trophi），用于咀嚼食物。颚器的形状和数量在轮虫的分类中是一个重要的依据，因为它们在不同类群中表现出差异。

The digestive system of a rotifer includes the mouth, pharynx, stomach, intestine, and anus. The mouth is located in the central region of the head circlet and has the functionality of opening and closing. The pharynx is a muscular organ containing a pair of hard structures called trophi, which are used for chewing food. The shape and number of trophi are important criteria for the classification of rotifers, as they exhibit variations among different groups.

轮虫的胃肠道呈直管状，从咽喉延伸至尾部附近，负责消化和吸收食物。一些轮虫的胃部还具备原始的消化腺。肠的末端开口于肛门，用于排出消化后的废物。

The straight tube-shaped alimentary canal of the rotifer extends from the pharynx to near the tail, responsible for the digestion and absorption of food. Some rotifers have primitive digestive glands in the stomach. The intestine opens at the anus near the tail, serving to expel digested waste.

轮虫的排泄系统由一对原肾管（protonephridia）组成，这是一种原始的排泄器官，包括一些细长的排泄管道和内部的焰细胞（flame cell）。焰细胞内含有鞭毛，能够产生水流，将体液中的多余水分和废物过滤出来，并通过管道输送到外界。尽管颜色与常见的钠焰有很大差异，但焰细胞得名于显微镜下观察到的鞭毛的摆动。

The excretory system of the rotifer consists of a pair of protonephridia, which is a primitive excretory organ comprising slender excretory ducts and internal flame cells. The flame cells contain cilia that generate a flow of fluid, filtering out excess water and waste from the body fluids and transporting them through the ducts to the external environment. Despite their significant color difference from typical sodium flame cells, they are named after the observed ciliary motion under a microscope.

轮虫采用两种不同的繁殖方式：无性生殖和有性生殖。这种选择与轮虫所处的生态环境密切相关。

Rotifers employ two different reproductive modes: asexual reproduction and sexual reproduction. This choice is closely related to the ecological environment in which the rotifers exist. 

在无性生殖中，雌性轮虫通过孤雌生殖生成与母体基因完全相同的后代。这一繁殖方式在我国现阶段定量考察阶元的单巢纲（Monogononta）、双巢纲（Digononta）和尾盘纲（摇轮虫纲，Seisonidea）中广泛存在，是轮虫最为常见的繁殖方式。无性生殖的优势在于能够迅速增加轮虫数量，使其在相对稳定的环境中快速占据优势地位。

In asexual reproduction, female rotifers reproduce through parthenogenesis, generating offspring that are genetically identical to the mother. This reproductive mode is widely prevalent in the Monogononta, Digononta, and Seisonidea, which are quantitatively investigated in the exams in China. Asexual reproduction is the most common reproductive mode among rotifers. The advantage of asexual reproduction lies in its ability to rapidly increase the population of rotifers, allowing them to quickly dominate in relatively stable environments.

相对地，有性生殖是指雌性轮虫与雄性轮虫交配，产生具有遗传变异的后代。这种繁殖方式主要发生在单巢纲中，并且通常仅在特定的环境刺激下发生，如温度变化、食物缺乏或拥挤等。有性生殖的优势在于能够生成新的基因组合，使轮虫能够更好地适应不断变化的环境条件。

On the other hand, sexual reproduction involves mating between female and male rotifers, resulting in offspring with genetic variations. This reproductive mode primarily occurs in the Monogononta and usually happens only under specific environmental stimuli, such as temperature changes, food scarcity, or overcrowding. The advantage of sexual reproduction lies in its ability to generate new combinations of genes, enabling rotifers to better adapt to continuously changing environmental conditions.

在有性生殖中，轮虫产生两种类型的卵：普通卵和休眠卵。

In sexual reproduction, rotifers produce two types of eggs: ordinary eggs and dormant eggs. 

普通卵是无性生殖时产生的卵，它们没有或只有薄薄的壳，发育速度快，最终孵化出雌性后代。而休眠卵则是有性生殖时产生的卵，它们具有厚厚的壳，并具备抗干旱的能力。

Ordinary eggs are produced during asexual reproduction, and they have little or no shell, develop quickly, and eventually hatch into female offspring. Dormant eggs, produced during sexual reproduction, have a thick shell and possess resistance to desiccation. 

休眠卵在适合的条件下孵化，形成新的个体，为轮虫在面对不利环境时提供了一种有效的生存策略。这两种繁殖方式的巧妙结合使得轮虫能够在多样的生态条件下成功繁衍。

Dormant eggs hatch under favorable conditions, giving rise to new individuals, providing an effective survival strategy for rotifers in unfavorable environments. The clever combination of these two reproductive modes allows rotifers to successfully reproduce in diverse ecological conditions.

轮虫是一种令人惊叹的精致而奇妙的生物，它们在水中呈现出多样且复杂的繁殖策略和行为。

这是基于 #经典动物知识# （可点击，下同）轮虫系列三篇推送的 #双语动物知识# 中轮虫的第二篇。

Rotifers are astonishingly delicate and marvelous creatures that exhibit diverse and intricate reproductive strategies and behaviors in aquatic environments. This is the second push of the #双语动物知识# series on rotifers, based on #经典动物知识#. 

By delving into the internal structure and reproductive methods of the Rotifera, we can contemplate the ever-changing microcosm in which these tiny organisms exist from different perspectives.

轮虫的滤食 via Reddit

轮虫以其独特的生理机制和适应性，成为微生物生态系统中引人入胜的研究对象，同时也为我们揭示了生命的多样性和生存的奥秘。在这个微小而精彩的世界中，它们为我们提供了一个微观的奇妙窗口，让我们欣赏自然的动物之美。

With their unique physiological mechanisms and adaptability, rotifers become captivating subjects for research in microbial ecosystems, simultaneously unveiling the diversity of life and the mysteries of survival. In this minuscule yet fascinating world, they provide us with a microscopic and enchanting window to appreciate the beauty of nature's creatures.