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Biology LibreTexts

50: Helminths

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  • Objectives

    • Differentiate between flatworms and roundworms
    • Differentiate between flukes and tapeworms
    • Identify some common worms
    • Recognize common features of each worm


    There are many worms in the kingdom Animalia, but we are looking at pathogenic representatives in 2 phyla (a major group within a kingdom is a phylum)---Platyhelminthes and Nematoda. Platyhelminthes are flatworms, divided into the cestode (tapeworms) class and the trematode (flukes) class. The life cycle of a worm can be very complex, with multiple hosts for different stages of the worm.

    Helminths are multicellular, and one might wonder why they are covered in microbiology. First, most worm infections are transmissible diseases, via insects, water, food, soil---similar to bacterial and viral infectious diseases. Second, diagnosis of helminthic diseases relies on the microscopic identification of the eggs or larvae. The adult worms are macroscopic. Mainly, you will see genital organs inside of the adult worms under the microscope, probably with lots of eggs. The Nematodes are roundworms. They come in separate sexes, and are a bit more evolved than the platyhelminthes.


    • trematodes (flukes) – flat, leaf-shaped, unsegmented, separate sexes
    • cestodes (tapeworms) – flat, segmented, hermaphroditic
    • nematodes (roundworms) – unsegmented, separate sexes

    Low power 10X or even scanning power (using the stereoscopic dissecting microscopes) should be sufficient for these large organisms. There are pictures of corresponding eggs on the side bench: You do not need to be able to identify the worms by their eggs. On the other hand, if you are planning a career in clinical lab sciences (medical technology), you will definitely have to learn the eggs later.


    • preserved specimens of various worms
    • pictures of eggs of adult worms (just for show, NOT for identification)
    • prepared slides of the adult: (use stereoscopic microscopes for scanning power and 10X low power on your regular microscopes)
      • Taenia (tapeworm)
      • Schistosoma (blood fluke)
      • Fasciola (liver fluke)
      • Enterobius (pinworm)
      • Trichinella (pork roundworm)
      • Ancylostoma (hookworm)
      • Dirofilaria (heartworm in dogs)
      • larvae in blood or Wuchereria (filariasis in humans)


    1. Observe the pre-prepared slides under themicroscope.
    2. Classify the specimens as per the chart below.

    * Major features of each organism are listed to the right


    1. Draw the organisms.
    2. Is Schistosoma a trematode, cestode or a nematode?
    3. Which group of helminths has a scolex?
    4. The meaning of hermaphroditic?
    5. Which group of parasites has flat and segmented body?