Parasites That Infest Us
Your body is a temple. It's also a home—a home for an immeasurable number of bacteria, yeast, and even parasites. Sounds heavenly, right? Sometimes, these microbes pass right through us and nothing happens. Other times, we get infected, if not infested, by them. Two types of parasites that can infect us are generally called cestodes and trematodes. Let's compare and contrast them in this lesson.
Cestodes & Trematodes
Cestodes are parasitic worms of the taxonomic class of Cestoda. Maybe you've heard of tapeworms? These creatures are a subclass of cestodes. They're whitish, flat, segmented worms that get into non-human animals by eating or drinking contaminated food or water. We get them from eating those animals and not having cooked the meat long enough to kill the worms or worm eggs.
Trematodes are parasitic worms of the taxonomic class of Trematoda. Again, you may be familiar with trematodes if you've heard of flukes, which are parasites of mollusks and vertebrates, like us.
Let's go over their similarities and differences. First, both of these parasitic worms belong to the same kingdom, that of Animalia, and to the same phylum, that of the Platyhelminthes, or flatworms.
Both cestodes and trematodes are multicellular animals. That is to say, they are made up of multiple cells, unlike the unicellular bacteria. These animals are bilaterally symmetrical as well. In other words, if you were to look at them from the outside, and cut them right down the middle with an imaginary line, each side would mirror the other.
Both cestodes and trematodes are helminths. This term can actually be defined in more than one way, depending on what subfield of biology you're coming from. But in medicine, a helminth is a parasitic worm that causes illness in a person. Helminths usually set up shop in our intestinal tract.
Neither the cestodes nor trematodes have a body cavity. Instead, their insides are filled with spongy cells, in between which lie their internal organs. And both the cestodes and trematodes are hermaphrodites, meaning they have female and male sex organs. Additionally, cestodes and trematodes are oviparous, egg-laying animals.
Now for some differences. When it comes to their shape, the cestodes have a tape-like, segmented body, whereas the trematodes have a leaf-like and unsegmented body. The cestodes have a head that has suckers and, in some cases, hooks. The trematodes have a head with suckers but no hooks.
Cestodes don't have a digestive tract, which is why they need a host. They absorb nutrients processed by the host via their own body surface. The trematodes have a digestive tract, but it is incomplete as they don't have an anus.
When it comes to the general aspects of their life cycles, the cestodes normally require two hosts. Trematodes need three hosts for theirs. These different hosts serve different phases, like one host for larvae and one for adult.
Cestodes are parasitic worms of the taxonomic class of Cestoda and include tapeworms. Trematodes, commonly called flukes, are parasitic worms of the taxonomic class Trematoda. Both are in the kingdom Animalia and phylum Platyhelminthes. Both are bilaterally symmetrical and multicellular animals.
Both cestodes and trematodes are hermaphroditic and oviparous (egg-laying). Cestodes are tape-like and segmented in shape, have a head with suckers and possibly hooks, and lack a digestive tract. Trematodes are leaf-like and unsegmented, lack hooks entirely, and have an incomplete digestive tract. Generally, cestodes require two hosts and trematodes need three to complete their life cycles.
Medical Disclaimer: The information on this site is for your information only and is not a substitute for professional medical advice.
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Cestodes and Trematodes: True or False Activity
This activity will help you assess your knowledge regarding the differences and similarities of cestodes and trematodes.
Determine whether the following statements are true or false. To do this, print or copy this page on a blank paper and underline or circle the answer.
True | False 1. Helminths are a group of parasitic insects that are highly adapted and dependent on their hosts.
True | False 2. Cestodes and trematodes can inhabit the intestinal tract of humans and animals.
True | False 3. Parasites, such as cestodes and trematodes, are organisms that consist of a single cell.
True | False 4. Protozoa are organisms that form the biological kingdom Animalia.
True | False 5. Tapeworms have a leaf-like and unsegmented body.
True | False 6. A fluke has no anus; waste material is excreted through the mouth.
True | False 7. All cestodes and trematodes give birth to live offspring.
True | False 8. Flukes and tapeworms are hermaphrodites, possessing both male and female reproductive organs.
True | False 9. Bilateral symmetry refers to organisms with body shapes that are mirror images along a midline.
True | False 10. Cestodes have a head with suckers but no hooks.
- False, because the correct statement is: Helminths are a group of parasitic worms that are highly adapted and dependent on their hosts.
- False, because the correct statement is: Parasites, such as cestodes and trematodes, are organisms that consist of multiple cells.
- False, because the correct statement is: Metazoa are organisms that form the biological kingdom Animalia.
- False, because the correct statement is: All cestodes and trematodes lay their eggs.
- False, because the correct statement is: Trematodes have a head with suckers but no hooks.
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