Flat, Round, and Segmented Worms

Biology Week 17 - Worms
Day 1 - 3 | Day 4 | | Lab 1 | Lab 2 | Quizstar


Worm Platyhelminthes Flatworm Planarian Fluke seta	Tapeworm Nematoda Roundworm Hookworm Trichinella Heartworm pinworms	Annelida Segmented worm Acoelomate Pseudocoelomate Coelomate cephalization

Flat, Round, and Segmented Worms

The term "worm" does not refer to a specific taxonomic group of animals.

Even though a single earthworm is hermaphroditic, producing both sperm and egg cells, it takes two earthworms to reproduce. Why?

The Phyla:

Platyhelminthes: the flatworms
The phylum includes free-living worms like the planarian,
parasitic worms like flukes,
and tapeworms.

Nematoda: the roundworms
No matter the size, all roundworms have slender bodies that taper at both ends. The internal structure of nematodes is quite complex.
Although most roundworms are free-living, there are many parasitic forms. These include pinworms, hookworms, trichinella, and heartworms.
Competition for resources is fierce in the micro-world of the nematode. In addition to avoiding larger animals, they might also be trapped by the nematode distroying fungi or harpooned by Haptoglossa mirabilis.

Annelida: the segmented worms

Members of this phylum, including the earthworm,
are free-living animals.
Even most leeches are carnivores. While some suck blood, they are only "external" parasites.

A comparison of "worms" should include:

Mortician Lab #1
Lab #2

Type of body cavity (coelom):

Flatworms are acoelomate - they have three germ layers, but no coelom.
Roundworms are pseudocoelomate - they have a cavity that forms between the mesoderm and the endoderm.
Segmented worms are coelomate - they have a true coelom which forms within the mesoderm.

Type of nervous system:

Most worms have sense receptors and nerves concentrated at their anterior end. This is known as "cephalization".
Some worms show a great ability to regenerate lost or injured parts, others do not.

Type of digestive system:

Some worms are parasitic, meaning that they live on or in another organism.
Some worms are "free-living", meaning that they are not dependant on another organism.

Type of reproduction:

Some worms reproduce asexually, others sexually, and still others can do both. Earthworms reproduce sexually.
The eggs of an earthworm are enclosed for 2 to 3 weeks in a cocoon secreted by the clitellum.
The visible measurement units in the picture of earthworm cocoons here are millimeters.

Type of locomotion:

Complexity and habitat determine locomotion.

Day 1-3 Computer Assignment - Worms
This assignment is due the day after tomorrow to get credit.
PowerPoint Scoring Rubric
Make a PowerPoint presentation about worms. Students can work in pairs or alone. Some Information outside our web page will be needed to complete your work. Use as many slides as needed to make a quality presentation about the following topics related to worms:

Title/Introduction slide
Compare and contrast the three phyla that worms are broken into: Platyhelminthes, Nematoda, Annelida.
Show the different types of body cavities found in worms
Show cephalization
Describe the life cycle of a tapeworm (use human tapeworm)
Show how the digestive system of a "free-living" worm is different from that of a parasitic worm
Describe sexual reproduction in earthworms
(Hint: the clitellum does not cover both worms during this process as you have seen on some zoology charts.)
Compare locomotion in planarians and earthworms.
Bibliography (Cite correctly)

Use diagrams and pictures to support topics (as indicated on rubric).
Have "transitions" from one slide to the other.
Make the slide show run automatically. Set the times in such a way that a viewer can comfortably read the information on each slide before the slide changes. Do not make the time so long that the reader gets bored between slides.
Always save the file in two places(use your first initial last name period and assignment, example: jsmith7worm.ppt).
Print a copy of power point (in handout form, six slides to a page) and evaluation rubric to turn in (rubric stapled on top).
Make sure to self evalute power point with rubric.
Use computer to show the presentation to your science facilitator.

Day 4 - Worms

How many hearts does an earthworm have?

The diagram below will serve as a review of the earthworm dissection you have done in the lower grades. As in your dissection, the diagram shows an earthworm with the dorsal surface cut open to expose the internal organs. You will notice that the segments are numbered along the bottom of the drawing.

Test your knowledgeof simple animals.

Day 4 Assignment - Worms (Test Your Concept Understanding)
Use the earthworm dissection diagram to answer the following questions.

What part of the nervous system is located in segment 3?
How many "hearts" does an earthworm have?
What parts of the digestive system are located between the following segments?

4 to 6
7 to 12
13 to 15
16 to 18
begins at segment 19 and goes to the posterior end

All animals have one of two types of circulatory systems. What type of circulatory system does an earthworm have?
A single earthworm produces both sperm and eggs. Use information shown on the diagram to explain why one earthworm cannot produce offspring.
Use this earthworm cross-section diagram to answer the following questions.

How many cell layers thick is the epidermis of an earthworm?
The circular muscles of an earthworm contract to squeeze inward. This increases pressure on the body fluids and stretches the worm. The longitudinal muscles contract to shorten the earthworm. Movement of the worm is accomplished by the combination of these two muscle contraction. From information provided on the drawing, which set of muscles do you think is strongest, and why?
How many pairs of seta are found on each body segment of the earthworm?
The nerve cord and the majority of other body nerves are located along the ventral part of the earthworm body. What advantage does this serve?

Watch this video on worms and answer the following questions.

What phyla do the flat worms belong to?
What phyla do the round worms belong to?
What phyla do the segmented worms belong to?
What type of digestive system is found in round worms?
What type of animal is the first to possess a true heart?
What are some ways humans can be infected with parisitic worms?

Research Links:

Pond Life Identification - Microscope Magazine
Flatworms and Roundworms - DVHS Zoology Class
Search - The Animal Diversity Web
Search - BIODIDAC, digital biology resources
Nematode Basics - USDA Nematology Lab
Horsehair Worms - Illinois Natural History Survey
Earthworm Information - Nicks Earthworm Web Page
Earthworm Care and Feeding - New York Worms
Earthworms and Crop Management - Purdue University
The Earthworm Hole - The New Zealand Institute for Crop & Food Research
Earthworms: Indicators of Soil Health - Illinois Natural History Survey
Earthworm Dissection Pictures - Cornell University
Leeches - Virginia Institute of Marine Science

An earthworm's body is not structured in a way that allows it to bring its own sperm and egg cells together.

An earthworm has 5 "aortic arches" that function as hearts.

Platyhelminthes: the flatworms The phylum includes free-living worms like the planarian, parasitic worms like flukes, and tapeworms.
Nematoda: the roundworms No matter the size, all roundworms have slender bodies that taper at both ends. The internal structure of nematodes is quite complex. Although most roundworms are free-living, there are many parasitic forms. These include pinworms, hookworms, trichinella, and heartworms. Competition for resources is fierce in the micro-world of the nematode. In addition to avoiding larger animals, they might also be trapped by the nematode distroying fungi or harpooned by Haptoglossa mirabilis.
Annelida: the segmented worms Members of this phylum, including the earthworm, are free-living animals. Even most leeches are carnivores. While some suck blood, they are only "external" parasites.