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  • 虫类

    A specimen jar containing a large roundworm with visible anatomy preserved in liquid.

    What is heartworm?
    ::什么是心脏病?

    You may have heard that you need to protect your pets from heartworm. Heartworms are a type of roundworm. They can be parasites in cats and dogs. That means, once they infect your pet, they can cause harm. However, there are preventative treatments available.
    ::你可能听说你需要保护你的宠物免受心虫的伤害。心虫是一种圆虫。它们可以是猫和狗的寄生虫。这意味着一旦它们感染了你的宠物,它们就会造成伤害。然而,有预防性的治疗。

    Roundworms
    ::虫类

    The word "worm" is not very scientific. This informal term describes animals (usually invertebrates) that have long bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms ( Figure ). They are classified in the phylum Nematoda , which has over 28,000 known species . Some scientists believe there could be over a million species of Nematodes.
    ::“ 寄生虫” 一词不很科学。 这个非正式的术语描述动物( 通常是无脊椎动物) , 它们有长的无胳膊或腿的动物。 有圆形、非分块的虫被称为线虫或圆虫( 图 ) 。 它们被归类在有28 000多种已知物种的植物性内马托达。 一些科学家认为, 可能有超过100万种的线虫。

    Nematodes are slender bilaterally symmetrical worms, typically less than 2.5 mm long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 cm, and some parasitic species are larger still, reaching over a meter in length. The worm body is often covered with ridges, rings, bristles, or other distinctive structures. The radially symmetrical head of a nematode also has distinct features. The head is covered with sensory bristles and, in many cases, solid "head-shields" around the mouth region. The mouth has either three or six lips arranged around the mouth opening, which often have a series of teeth on their inner edges.
    ::线虫是双对称线虫,一般长度小于2.5毫米。最小的线虫是显微镜,而自由生存的物种可以达到5厘米,而一些寄生虫的物种仍然较大,超过一米长。蠕虫身体往往被脊、环、晶体或其他独特的结构覆盖。线虫的极对称头也具有不同的特点。头部上覆有感官的胸罩,在许多情况下,在口部周围有固态的“头部屏障 ” 。口腔周围有三、六张嘴唇,口部周围往往有一系列牙齿。

    Scanning electron microscope image of a nematode, showing its elongated body and distinct features.

    Nematodes can be parasites of plants and animals.
    ::线虫可以是植物和动物的寄生虫。

    Features of Roundworms
    ::圆虫的特点

    1. Unlike the , the roundworms have a body cavity with internal organs .
      ::与昆虫不同的是, 虫体内有内脏器官的洞穴。
    2. A roundworm has a complete , which includes both a mouth and an anus. This is a significant difference from the incomplete digestive system of flatworms. The roundworm digestive system also include a large digestive organ known as the gut. Digestive enzymes that start to break down food are produced here. There is no stomach , but there is an intestine which produces enzymes that help absorb nutrients . The last portion of the intestine forms a rectum , which expels waste through the anus.
      ::圆虫有一个完整的, 包括一个嘴和肛门。 这与不完全的扁虫消化系统有很大的区别。 圆虫消化系统还包括一个称为肠胃的大型消化器官。 开始分解食物的消化酶在这里产生。 没有胃部, 但肠子产生酶, 有助于吸收养分。 肠子的最后部分形成直肠, 将废物排入肛门 。
    3. Roundworms also have a simple with a primitive brain . There are four nerves that run the length of the body and are connected from the top to the bottom of the body. At the anterior end of the animal (the head region), the nerves branch from a circular ring which serves as the brain. The head of a nematode has a few tiny sense organs , including chemoreceptors, which sense chemicals. Though still a relatively simple structure, the nervous system of roundworms is very different from that of the nerve net .
      ::圆虫也有一个简单而原始的大脑。 有四个神经神经运行着身体的长度,并且从身体的顶部连接到下部。 在动物的前端(头部区域),神经分支来自作为大脑的环形环形。线虫的头部有一些小的感官器官,包括感知化学物质的耳机。尽管这个结构相对简单,但圆虫的神经系统与神经网的神经系统非常不同。

    Roundworms in the Environment
    ::环境中的虫群

    Roundworms can be free-living organisms , but they are probably best known for their role as significant plant and animal parasites. Most Nematodes are parasitic, with over 16,000 parasitic species described. Heartworms, which cause serious disease in dogs while living in the heart and , are a type of roundworm. Roundworms can also cause disease in humans. Elephantiasis, a disease characterized by the extreme swelling of the limbs ( Figure ), is caused by infection with a type of roundworm.
    ::圆虫可以是自由生物体,但它们很可能因其作为重要的动植物寄生虫的作用而最为人所知。大多数的线虫是寄生虫,有超过16,000种寄生虫。在生活在心脏和......的狗中引起严重疾病的心虫是一种圆虫。圆虫也可能造成人类的疾病。象虫是一种以四肢极端膨胀为特征的疾病(图 ) , 是由一种圆虫感染造成的。

    Swollen legs of a person affected by elephantiasis, illustrating a roundworm disease.

    One roundworm parasite causes elephantiasis, a disease characterized by swelling of the limbs.
    ::一种寄生虫导致大象病,其特点是四肢肿胀。

    Most parasitic roundworm eggs or larvae are found in the soil and enter the when a person picks them up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly through the skin. The best solution to these diseases is to try to prevent these diseases rather than treat or cure them.
    ::大部分寄生虫蛋或幼虫蛋或幼虫在土壤中被发现,它们进入人体时,当一个人把寄生虫蛋或幼虫放在手上,然后将其转移到嘴里,卵或幼虫也可以直接通过皮肤进入人体,这些疾病的最好解决办法是设法预防这些疾病,而不是治疗或治愈这些疾病。

    Diseases caused by roundworms are more common in developing countries. Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include
    ::由虫引起的疾病在发展中国家较为常见,许多由虫引起的寄生虫疾病是由于个人卫生条件差造成的。

    • lack of a clean water supply,
      ::缺乏清洁饮水供应,
    • inadequate sanitation measures,
      ::卫生措施不足;
    • crowded living conditions, combined with a lack of access to health care and low levels of education.
      ::人口拥挤的生活条件,加之缺乏医疗保健和教育水平低。

    Summary
    ::摘要

    • Roundworms have a body cavity with internal organs and a simple nervous system.
      ::虫体腔有内脏器官和简单的神经系统。
    • Roundworms can be free-living or parasitic.
      ::圆虫可以是自由生存的,也可以是寄生虫。

    Explore More
    ::探索更多

    Use the resources below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    Explore More I
    ::探索更多

    • Nematode Movement at (1:52)
      ::线虫移动时间(1:52)

     

    1. How does the movement of a nematode differ from the movement of an earthworm?
      ::线虫的移动与蚯蚓的移动有何不同?
    2. Why can't a nematode move like an earthworm?
      ::为什么线虫不能像蚯蚓一样移动?
    3. What is the purpose of the nematode's cuticle?
      ::线虫的切口有什么用?

    Review
    ::回顾

    1. What is a roundworm?
      ::什么是圆虫?
    2. How are the internal structures of the roundworms different from flatworms?
      ::圆虫的内部结构与扁虫有何不同?
    3. What is the main cause of many parasitic diseases caused by roundworms?
      ::许多寄生虫病是由寄生虫引起的,其主要原因是什么?