Unit 3:  Diversity of Life

Module 5:  Kingdom Animalia

Learning Objectives:  4.1

Lesson 2:  The Three Worm Phyla

Lesson Objectives:

  • To describe the characteristics of the three worm phyla.
  • To examine the evolutionary development through the first five phyla of the animal kingdom.

Evaluation:

Assignment: 

  • Part 1:  Questions of the Worm Phyla (7 marks)
  • Part 2:   Case Study - Tracing Evolutionary Trends  (18 marks)

The next three invertebrate phyla we will study all contain worm-like organisms.  Because these worms share very few characteristics, they are placed in separate phyla.

The following information will provide an overview of the general and some specific characteristics of each of the worm phyla.
3.  Phylum Platyhelminthes (the flatworms) 
Readings:  “Bilateral Symmetry and the Primitive Brain:  Phylum Platyhelminthes”  p. 475 – 476 Nelson Biology

Three main groups of flatworms:

  1. planarian
  2. tapeworms
  3. flukes

Key features of all flatworms:

  • three body layers (germ layers);  called the endoderm, ectoderm and the mesoderm
  • display the development of organs and organ systems
  • they are acoelomate – solid body without a space in the centre
  • some are degenerate (part of their digestive system is lost when they are parasitic)
  • have specialized life cycles to match their host
  • show cephalization – development of a head end (with a concentration of nerve cells)

5-2.1 General features of an intact tapeworm
5-2.2  Whole mount of the liver fluke
5-2.3 The Nervous System of Dugesia, a planarian
4.  Phylum Nematoda (the roundworms)

Reading:  "Phylum Nematoda" p. 477-478  Nelson Biology

Key Features:

  • the first organism to have a digestive system with an opening at both ends
  • have a pseudocoelem  (a fluid filled body cavity)
  • long and slender and tapered at both ends
  • live in soil, water or as parasites in other plants or animals
  • bilaterally symmetrical
  • have three germ layers – ectoderm, endoderm and mesoderm

    • ex.  hookworm, pinworm, Ascaris and vinegar eel

Digestion

  • Digests food in long tube structure; wastes are removed through the anus

Nervous System

  • Like the flatworms, they also have a collection of nerves at the anterior end (simple brain) and nerve cords extending the length of the body
5.  Phylum Annelida (the segmented worms)
Readings:  "The Segmented Worms:  Phylum Annelida" p. 478-480 Nelson Biology

Main groups:

  1. earthworms
  2. tube worms
  3. leech

Key Features:

  • divided into segments that are partially separated from each other
  • segmentation allows for specialization
  • true coelomates
Image 5-2.4   External view of a preserved earthworm (Lumbricus terrestris)
Image 5-2.5  External features of a leech

If you have access to a biology lab with sets of preserved organisms be sure to look at samples of all three of the worm phyla.

The majority of the images in this lesson were obtained from the BIODIDAC web site.  ("A bank of digital resources for teaching biology.")

Images obtained from BIODIDAC: 5-2.1 to  5-2.5

If you would like to explore more images of any of the worm phyla, click on the link below:

http://biodidac.bio.uottawa.ca/thumbnails/catquery.htm?kingdom=Animalia

Then click on Annelida, Platyhelminthes, or Nematoda from the alphabetical list at the top.

Assignment:  Part 1:  Questions on The Worm Phyla  (7 marks)

1.      Symptoms of tapeworms in an animal usually include loss of weight and general fatigue.  Account for these conditions.

2.      Research the life cycle of one of the many parasitic worms.  Indicate the classification and the scientific name for the parasite.  Illustrate the life cycle complete with numbers, labels and diagrams.

3. Describe the characteristics of leeches that give them special “healing powers.”

Assignment:  Part 2:  Case Study:  Tracing Evolutionary Trends (18 marks)

Complete all procedure and application questions in “Case Study:  Tracing Evolutionary Trends” p. 481 Nelson Biology.   Submit your answers for part 1 and 2 for  evaluation.
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