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  • General

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  • 虫类

    A gold-dotted flatworm rests on coral, showcasing its vibrant colors and unique shape.

    Would you believe that this gold-dotted creature is a flatworm?
    ::你相信这个金点的动物 是只扁虫吗?

    No? Well it is. There are more than 25,000 different types of flatworms, so they can be very different in how they appear. And many don't even look like your typical worm.
    ::是的,有超过25000种不同的扁虫, 它们的出现方式可能非常不同。很多都不像你典型的蠕虫。

    Flatworms
    ::虫类

    Flatworms belong to the phylum Platyhelminthes . Examples of flatworms are shown in Figure . There are more than 25,000 in the flatworm phylum. 
    ::扁虫属于,扁虫的例子见图10。在中,有25,000多只。

    Examples of flatworms, including a flatworm, tapeworm head, and fluke.

    Platyhelminthes. Platyhelminthes include flatworms, tapeworms, and flukes.
    ::等离子体 等离子体包括扁虫、虫和

    Structure and Function of Flatworms
    ::平虫的结构和功能

    Flatworms range in length from about 1 millimeter (0.04 inches) to more than 20 meters (66 feet). They have a flat body because they do not have a coelom or even a pseudocoelom . They also lack a . Instead, their exchange gases by directly with the environment. They have an incomplete digestive system .
    ::单虫的长度从大约1毫米(0.04英寸)到20米(66英尺)不等,它们有一个平板体,因为它们没有阴极,甚至没有假阴极,它们也缺少。相反,它们直接与环境交换气体,它们有一个不完整的消化系统。

    Flatworms reflect several major evolutionary advances in invertebrates . They have three embryonic cell layers, including mesoderm . The mesoderm layer allows them to develop organ systems . For example, they have muscular and excretory systems. The muscular system allows them to move from place to place over solid surfaces. The lets them maintain a proper balance of and salts. Flatworms also show cephalization and bilateral symmetry .
    ::反映了无脊椎动物的几大进化进步,它们有三个胚胎细胞层,包括中子;中子层允许它们开发器官系统;例如,它们有肌肉和排泄系统;肌肉系统允许它们从地方移动到固体表面的方位;它们保持适当的平衡和盐类。 扁虫还表现出了气化和双边的对称性。

    Flatworm Reproduction
    ::扁虫繁殖

    Flatworms reproduce sexually. In most species, the same individuals produce both eggs and . After occurs, the fertilized eggs pass out of the adult’s body and hatch into larvae . There may be several different larval stages. The final larval stage develops into the adult form, and the repeats.
    ::在大多数物种中,受精卵既产卵,又产卵。之后,受精卵从成人身体中排出,孵化成幼虫。可能有几种不同的幼虫阶段。最后的幼虫阶段会发展成成人形式和重复。

    Ecology of Flatworms
    ::平虫生态学

    Both flukes and tapeworms are parasites with vertebrate hosts, including human hosts. Flukes live in the host’s or liver . Tapeworms live in the host’s . Usually, more than one type of host is required to complete the parasite’s life cycle. Look at the life cycle of the liver fluke in Figure . As an adult, the fluke has a vertebrate host. As a larva, it has an invertebrate host. If you follow the life cycle, you can see how each host becomes infected so the fluke can continue its life cycle.
    ::虫和虫都是寄生虫,有脊椎动物宿主,包括人体宿主。 虫生活在宿主或肝脏中。 虫生活在宿主的体内。 通常需要不止一种宿主才能完成寄生虫的生命周期。 看看图中的肝脏宿主的生命周期。 作为成年人,虫有一个脊椎宿主。 作为幼虫,它有一个无脊椎动物宿主。如果你跟随生命周期,你可以看到每个宿主是如何感染的,这样流感的生命周期才能继续下去。

    Life cycle of the sheep liver fluke, detailing hosts and larval stages in infection.

    Life Cycle of the Sheep Liver Fluke. The sheep liver fluke has a complicated life cycle with two hosts. How could such a complicated way of life evolve?
    ::羊肝和两个宿主的生命周期很复杂。 如此复杂的生活方式怎么会演变成这样呢?

    Tapeworms and flukes have suckers and other structures for feeding on a host. Tapeworms also have a scolex , a ring of hooks on their head to attach themselves to the host (see Figure ). Unlike other invertebrates, tapeworms lack a mouth and digestive system. Instead, they absorb nutrients directly from the host’s digestive system with their suckers.
    ::虫和虫都有吸食宿主的吸食器和其他结构。 虫头上还有一条螺旋形的钩子圈,可以附在宿主身上(见图 ) 。 与其他无脊椎动物不同,虫缺乏嘴和消化系统。 相反,它们直接吸收宿主消化系统的养分,用吸食器吸收养分。

    Head of a tapeworm showing suckers and a scolex with hooks for attachment.

    Tapeworm Suckers and Hooks. The head of a tapeworm has several suckers. At the very top of the head is a “crown” of hooks called a scolex.
    ::虫和钩子。 虫的头有几只。 头顶上是一条叫“ 螺旋杆”的钩子。 头部有几只。 头部顶部是一条叫做“ 螺旋杆 ” 的钩子。

    Not all flatworms are parasites. Some are free-living carnivores . They eat other small invertebrates and decaying . Most of the free-living species live in habitats , but some live in moist soil .
    ::并不是所有的扁虫都是寄生虫,有些是自由生存的食肉动物,它们食用其他小无脊椎动物和腐烂。大多数自由生存物种生活在生境中,但有些则生活在潮湿的土壤中。

    Summary
    ::摘要

    • Platyhelminthes are flatworms such as tapeworms and flukes.
      ::等离子虫是扁虫,如虫和虫。
    • Flatworms have a mesoderm cell layer and simple organ systems. They also show cephalization and bilateral symmetry.
      ::扁虫有中度细胞层和简单的器官系统,还显示呼吸系统化和双边对称。
    • Many flatworms are parasites with vertebrate hosts. Some are free-living carnivores that live mainly in aquatic habitats.
      ::许多扁虫是寄生虫,有脊椎动物宿主,有些是主要生活在水生生境的免费食肉动物。

    Review
    ::回顾

    1. Flatworms were the first to evolve the mesoderm. What advantage does the mesoderm provide?
      ::长效虫是第一个进化中度虫。 中度虫能提供什么好处?
    2. Describe specialized feeding structures of parasitic platyhelminthes.
      ::描述寄生虫聚苯乙烯的专门喂养结构。
    3. Some parasitic flatworms have a very complicated life cycle with more than one host. Infer why this might be adaptive.
      ::有些寄生虫的生命周期非常复杂,有不止一个宿主。推论为什么这可能是适应性的。