轮虫动物（上）：带轮盘的动物  Rotifera (Part 1/3): Animal with Wheels

朋友们是否曾想过，微小的生物中隐藏着怎样的隐秘世界？

Have you ever wondered what secrets lie hidden in the tiny world of microorganisms?

在动物界的微观世界中有一种不可思议的生物，身形纤小却蕴含着复杂的结构和功能，具备令人叹为观止的抗逆性。这神秘的生灵正是轮虫。尽管其身体仅有几十到几百微米，轮虫却展现出令人难以置信的微观奇迹。

In the microscopic realm of the animal kingdom, there exists an incredible creature—small in size yet harboring intricate structures and functions, possessing astonishing resistance. This enigmatic being is none other than the rotifer. Despite measuring only tens to hundreds of micrometers in length, the rotifer showcases unbelievable microcosmic wonders.

今天，让我们一起探索轮虫的奇妙之旅。

Today, let's embark on a fascinating journey to explore the marvels of the rotifer.

轮虫是一类原腔动物，在我国现阶段考察的经典动物学中，隶属于轮虫动物门（Rotifera Cuvier, 1798）。轮虫动物门包括大约2000种已知物种，主要分布在淡水和海水环境中，也有少数生存在湿润的土壤或植物表面。

Rotifers are a type of pseudocoelomate animal belonging to the phylum Rotifera (Cuvier, 1798) in the classic classification. The phylum Rotifera encompasses approximately 2000 known species, primarily distributed in freshwater and marine environments, with a minority inhabiting moist soil or the surfaces of plants.

这些微小而多样化的生物以其独特的特征而闻名，其身体呈轮状或椭圆形，通常具有透明的外壳。轮虫以其广泛的生态适应性而著称，能够在不同的水域和湿地环境中找到生存的机会。

These tiny yet diverse organisms are renowned for their distinctive features, with bodies often exhibiting a wheel or oval shape and typically possessing a transparent outer shell. Rotifers are noted for their broad ecological adaptability, allowing them to thrive in various aquatic and wetland environments.

在轮虫动物门中，约有2000个已知物种，它们展现出卓越的生存能力和繁殖策略。这些生物在水体中执行重要的生态功能，包括分解有机物和维持水体生态平衡。

Within the Rotifera, there are about 2000 known species, showcasing remarkable survival abilities and reproductive strategies. These organisms play crucial ecological roles in aquatic environments, including the decomposition of organic matter and the maintenance of ecological balance in water bodies.

轮虫是显微镜下最早被发现的微生物之一。这一重要的发现可追溯到17世纪末，由英国自然学家约翰·哈里斯（John Harris）首次观察到。

Rotifers are among the earliest microorganisms discovered under a microscope. This significant discovery dates back to the late 17th century and is credited to the British naturalist John Harris. 

当时的哈里斯是一位英国圣公会牧师，他于1696年描述了这些微小生物，形容其为“一种像大蛆一样的动物（这次大家知道某英国文学作品中“麻瓜”的谐音来源了），它可以将自己收缩成球形，然后再伸展开来；它的尾部末端出现了一个像蠼螋那样的夹子”。

At the time, Harris, a Church of England clergyman, first observed these tiny organisms in 1696. He described them as "an animal like a large maggot which could contract itself into a spherical figure and then stretch itself out again; the end of its tail appeared with a forceps like that of an earwig."

这种初步的描述描绘出轮虫独特的形态特征，特别是那个被称为“夹子”的结构，我们现在知道这其实指的是轮虫的趾。哈里斯的发现为微生物学的开创性研究奠定了基础，也为后来对轮虫及其生态学角色的深入了解提供了重要线索。

This initial description outlined the distinctive morphological features of rotifers, particularly the structure referred to as the "forceps," which we now know as the toes of the rotifer. Harris's discovery laid the foundation for pioneering research in microbiology and provided crucial clues for later in-depth understanding of rotifers and their ecological roles.

随着时间的推移，微生物学的发展进程进一步丰富了人们对轮虫的认识。在1702年，荷兰显微镜大师安东尼·范·列文虎克（在台湾地区被称为李文虎克，都是指 Antonie van Leeuwenhoek）在对其他动物类群进行研究时，也成功地观察到了轮虫。

Over time, the development of microbiology has further enriched our understanding of rotifers. In 1702, the Dutch microscopy pioneer Antonie van Leeuwenhoek (various translations in the Mainland and Taiwan region) successfully observed rotifers while studying other animal groups.

列文虎克的观察不仅局限于轮虫的整体结构，他还特别强调了轮虫头部两侧的环形结构。据称，他最早将这些结构形象地称为“轮”（现译为 wheels）。正是由于这一独特的观察，轮虫这个名字由此而来，成为了这一生物群体的正式命名。

Van Leeuwenhoek's observations extended beyond the overall structure of rotifers; he specifically emphasized the ring-like structures on both sides of the rotifer's head. It is said that he was the first to vividly describe these structures as "wheels" (now translated as "wheels"). It is due to this unique observation that the name "rotifer" originated, becoming the formal designation for this group of organisms.

轮虫的演化历史在科学界引起了一些争议，但通过分子系统发生学的研究，目前的理论倾向于认为轮虫可能是从古早线虫动物的祖先中分化出来的一个支系。

The evolutionary history of rotifers has sparked some controversy in the scientific community. However, current theories, supported by molecular phylogenetics research, tend to suggest that rotifers may have diverged from the ancestors of ancient nematode worms.

分子系统发生学是通过研究生物分子（例如DNA、RNA和蛋白质）的序列和结构来推断物种之间的亲缘关系的一种方法。

Molecular phylogenetics is a method of inferring the evolutionary relationships between species by studying the sequences and structures of biological molecules such as DNA, RNA, and proteins. 

通过比较轮虫与其他生物的分子特征，科学家们发现了与古早线虫动物相似的基因序列和结构，这为轮虫与线虫之间的亲缘关系提供了支持。

Through the comparison of molecular features between rotifers and other organisms, scientists have identified gene sequences and structures in rotifers that are similar to those found in ancient nematode worms, providing support for the hypothesis of a relationship between rotifers and nematodes.

在经典分类学的研究中，轮虫和线虫被认为具有一些共同的特征，这些特征在它们的基本生物学结构上显示出一定的相似性。例如，它们都具有假体腔（伪体腔），没有特化的循环系统和呼吸系统等特点。

In classical taxonomic studies, rotifers and nematodes are considered to share some common features, indicating a certain degree of similarity in their fundamental biological structures. For instance, both exhibit a pseudocoelom, lack specialized circulatory and respiratory systems, among other characteristics.

然而，轮虫也展现了一系列独特的特征，这些特征在其与线虫之间的区分上起到了关键作用。

However, rotifers also display a range of unique features that play a crucial role in distinguishing them from nematodes. Some of these distinctive features.

这些独特的特征使得轮虫在形态学上与线虫有所区别，同时也为其在生态学和生物学上的角色提供了独特的适应性。经典分类学的研究为科学家们提供了对这两个生物群体的基本认识，而分子生物学的进展则进一步强化了对它们演化历史和亲缘关系的理解。

These distinctive features set rotifers apart morphologically from nematodes and contribute to their unique adaptability in ecological and biological roles. Classical taxonomic studies have provided scientists with a fundamental understanding of these two biological groups, while advancements in molecular biology have further enhanced our understanding of their evolutionary history and relationships.

在我国的经典动物学中，轮虫动物门被划分为三个主要纲，分别是单巢纲（Monogononta）、双巢纲（Digononta）和尾盘纲（摇轮虫纲，Seisonidea）。而在这三个纲中，单巢纲和双巢纲被合称为真轮形动物（Eurotatoria）。

In classical zoology in China, the phylum Rotifera is divided into three main orders: Monogononta, Digononta, and Seisonidea (also known as the tail-plate order). Among these three orders, Monogononta and Digononta are collectively referred to as Eurotatoria.

单巢纲是轮虫动物门中最庞大的一个纲，包含大约1500种已知物种。这些轮虫主要栖息在淡水环境中，少数种类也适应在海水或土壤中生活。单巢纲轮虫的显著特征之一是其仅有一个卵巢，并且表现出两种截然不同的生殖方式：无性生殖和有性生殖。

Monogononta is the largest order within the phylum Rotifera, comprising approximately 1500 known species. These rotifers primarily inhabit freshwater environments, with a few species adapted to life in seawater or soil. One notable characteristic of the Monogononta rotifers is that they have only one ovary and exhibit two distinct modes of reproduction: asexual reproduction and sexual reproduction.

在无性生殖过程中，雌性轮虫通过孤雌生殖，产生与母体基因完全相同的后代。这种生殖方式有助于个体在适应环境中快速繁殖，从而适应不断变化的生态条件。

In asexual reproduction, female rotifers engage in parthenogenesis, producing offspring that are genetically identical to the parent. This reproductive strategy enables rapid population growth, allowing individuals to adapt quickly to changing environmental conditions.

相反，在有性生殖时，雌性轮虫会产生少量的雄性后代。这些雄性后代的功能主要是参与受精过程，而它们自身无法进食或存活很久。受精后的卵会发展成具有抗干旱能力的休眠卵，在适宜的条件下孵化，形成新的个体。

Conversely, in sexual reproduction, female rotifers produce a small number of male offspring. The primary function of these male offspring is to participate in the fertilization process, and they are unable to feed or survive for an extended period. Fertilized eggs develop into dormant eggs with resistance to desiccation. Under favorable conditions, these dormant eggs hatch, giving rise to new individuals.

单巢纲是轮虫动物门中最庞大的一个纲，包含大约1500种已知物种。这些轮虫主要栖息在淡水环境中，少数种类也适应在海水或土壤中生活。单巢纲轮虫的显著特征之一是其仅有一个卵巢，并且表现出两种截然不同的生殖方式：无性生殖和有性生殖。

Monogononta is the largest order within the phylum Rotifera, comprising approximately 1500 known species. These rotifers primarily inhabit freshwater environments, with a few species adapted to life in seawater or soil. One notable characteristic of the Monogononta rotifers is that they have only one ovary and exhibit two distinct modes of reproduction: asexual reproduction and sexual reproduction.

在无性生殖过程中，雌性轮虫通过孤雌生殖，产生与母体基因完全相同的后代。这种生殖方式有助于个体在适应环境中快速繁殖，从而适应不断变化的生态条件。

In asexual reproduction, female rotifers engage in parthenogenesis, producing offspring that are genetically identical to the parent. This reproductive strategy enables rapid population growth, allowing individuals to adapt quickly to changing environmental conditions.

相反，在有性生殖时，雌性轮虫会产生少量的雄性后代。这些雄性后代的功能主要是参与受精过程，而它们自身无法进食或存活很久。受精后的卵会发展成具有抗干旱能力的休眠卵，在适宜的条件下孵化，形成新的个体。

Conversely, in sexual reproduction, female rotifers produce a small number of male offspring. The primary function of these male offspring is to participate in the fertilization process, and they are unable to feed or survive for an extended period. Fertilized eggs develop into dormant eggs with resistance to desiccation. Under favorable conditions, these dormant eggs hatch, giving rise to new individuals.

双巢纲是一个相对较小的纲，其中的种类主要生活在海水中。双巢纲的特征是有两对卵巢，而且一般只有无性生殖方式。

The class Digononta (Bdelloidea), which is relatively small, primarily inhabits marine environments. A distinctive feature of Bdelloidea is having two pairs of ovaries, and they typically reproduce through parthenogenesis.

雌性轮虫通过孤雌生殖产生与母体基因完全相同的后代。近期，也有人直接用蛭形轮虫（Bdelloidea）代指扬弃过的此类群。

In parthenogenesis, female rotifers produce offspring that are genetically identical to the mother. Recently, some researchers have directly associated Bdelloidea with this discarded group of rotifers.

其中，头部是最显著的部分，具有两侧对称的环轮结构，被称为头冠（corona）。头冠是轮虫身体中的重要特征，由许多带有纤毛的突起组成，它们能够迅速旋转或摆动，产生水流来吸引食物或推进运动。

Among these, the head is the most prominent part, featuring a pair of symmetrically arranged circular wheel structures known as the corona. The corona is a significant feature of the rotifer's body, composed of numerous ciliated projections that can rapidly rotate or swing, generating water currents to attract food or propel movement.

Heraldic Royal Crown of Italy 可见形似 via Wikimedia

头冠的功能多样，其主要职责之一是通过产生水流，引诱和捕获食物。这种水流产生的方式可以使轮虫更有效地在其生活环境中获取营养。头冠上有多种刚毛类的感觉器官，例如感须或触角，这些器官有助于轮虫感知周围环境，并对外界刺激作出相应的反应。

The corona serves diverse functions, with one of its primary responsibilities being the generation of water currents to attract and capture food. This method of water flow allows the rotifer to more efficiently obtain nutrients in its living environment. Various bristle-like sensory organs, such as setae or antennae, are present on the corona, aiding the rotifer in perceiving the surrounding environment and responding to external stimuli.

左上可见头冠结构 by Bob Blaylock 

在一些轮虫的头冠上，这些感觉器官的存在增强了它们在环境中的适应性。通过感知外部刺激，轮虫能够更灵敏地应对环境变化，从而提高其生存和繁殖的成功率。

On the corona of some rotifers, the presence of these sensory organs enhances their adaptability in the environment. By sensing external stimuli, rotifers can respond more sensitively to environmental changes, thereby increasing their chances of survival and successful reproduction.

躯干是轮虫身体最长的部分，它承载了大部分内部器官和肌肉层。这一身体结构的精妙结构使得轮虫在不同的环境中能够有效地获取和处理食物，同时进行排泄和泄殖，为其在生态系统中的生存和繁衍提供了必要的生理支持。

The trunk is the longest part of the rotifer's body, carrying most of the internal organs and muscle layers. The intricate design of this body structure enables the rotifer to effectively acquire and process food, as well as engage in excretion and reproduction, providing essential physiological support for its survival and reproduction in ecosystems.

带节片的兜甲 by Wolfgang Sauber

躯干的外部结构在保护方面起到了关键作用，具有相对于体躯其他部分更加加厚的角质外壳，被称为兜甲（lorica）。这种兜甲充当一种防护层，为轮虫提供了额外的保障。

The external structure of the trunk plays a crucial role in protection, featuring a thickened cuticle known as lorica, which is thicker compared to other parts of the body. This lorica acts as a protective layer, providing additional safeguards for the rotifer.

躯干上有一个口腔和一个嗉囊（咀嚼囊，mastax），其中嗉囊内含有一对硬质结构称为颚器（咀嚼器，trophi）。颚器是轮虫用来咀嚼食物的工具，通过对食物的处理，有助于更有效地消化和吸收。这个食物在经过咀嚼囊的加工后，进入轮虫的消化道，接着在这里被消化和吸收。

On the body trunk, there is a mouth and a mastax (or chewing stomach), within which lies a pair of hard structures called trophi (or jaws). Trophi serve as tools for the rotifer to chew food, facilitating more efficient digestion and absorption through food processing. After being processed in the mastax, the food enters the rotifer's digestive tract, where it is further digested and absorbed.

Various types of the trophi of rotifers by C.T. Hudson

A. Single malleus of Brachionus urceolaris.（原文如此，下同）

B. Trophi of Brachionus urceolaris.

C. Single malleus of Euchlanis deflexa.

D. Trophi of Euchlanis deflexa.

E. Trophi of Notommata petromyzon.

F. Trophi of Diglena forcipata.

G. Trophi of Asplanchna priodonta.

H. Trophi of Stephanoceros Eichornii.

I. Trophi of Philodina roseola.

K. Trophi of Limnias Ceratophylli.

c. manubrium

d. uncus

c-d. malleus

e. ramus

f. fulcrum

e-f. incus

轮虫的胃肠道末端开口于肛门，也就是兼具泄殖和排泄功能的双功能的泄殖孔。在泄殖孔附近，还有一对合胞体的排泄器官，被称为原肾管（protonephridia），这些器官的作用是排出多余的水分和废物。

The digestive tract of the rotifer opens at the anus, a dual-function opening serving for both reproduction and excretion. Near the anus, there is a pair of excretory organs called protonephridia, which function as excretory canals to eliminate excess water and waste.

尾部是轮虫身体结构中最短的部分，它特征着一对或多对足趾（toes）。这些足趾具有多种功能，其中之一是用于在基质上稳固轮虫的身体或夹取食物。一些轮虫种类的足趾上可能还存在一些附属结构，例如粘液腺或粘盘，这些结构能够增加足趾的附着力或防止被捕食者吞食。

The tail is the shortest part of the rotifer's body structure, featuring one or more pairs of toes. These toes serve various functions, including stabilizing the rotifer's body on substrates or grasping food. Some species of rotifers may have additional structures on their toes, such as mucous glands or adhesive discs, which can enhance toe adhesion or prevent predation.

这种足趾的特点使得轮虫在不同的环境中具备更好的运动和食物获取能力。通过足趾的协同作用，轮虫能够在底部基质上移动，定位和稳固身体。一些附属结构的存在提供了额外的功能，例如通过粘液腺或粘盘增强附着力，有助于在不稳定的环境中保持身体的牢固位置。

The design of these toes equips the rotifer with improved mobility and food acquisition abilities in different environments. Through the coordinated action of the toes, the rotifer can move, locate, and stabilize its body on the bottom substrate. The presence of additional structures, such as mucous glands or adhesive discs, provides extra functionality, such as enhancing adhesion to surfaces, aiding in maintaining a secure position in unstable environments.

轮虫是一群微小而神奇的生物，在水域中呈现出多样且复杂的形态与行为。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# 中轮虫的第一篇。通过深入了解轮虫动物门的发现历史、演化、分类以及基本特征，我们能够更好地领略这个令人惊叹的微观世界的神奇之处。

Rotifers are a group of tiny and fascinating organisms that exhibit diverse and complex morphologies and behaviors in aquatic environments. This is the first push of the #双语动物知识# series on rotifers, based on #经典动物知识#. By delving into the discovery history, evolution, classification, and basic features of the phylum Rotifera, we can gain a better appreciation for the wonders of this astonishing microscopic world.