Phylum Nematoda – Webquest Notes

Part 2 of webquest:

Rather than me going through the notes and boring you, today you will be using this website to go over the notes, videos, and pictures at your own speed. You will gather notes through answering questions which gives you examples of questions I could ask on the simple invertebrates test while adapting my notes to fully address the question. Feel free to use other materials/videos to explore these phylum and help clarify if you need. If you would like me to check on any of your answers/diagrams, please let me know! Our first test will cover Phylum Porifera, Phylum Cnidaria, Phylum Platyhelminthes, and Phylum Nematoda.

Figure 1: Current cladogram

Nematoda – “Thread” – Greek origin. Nematodes are the roundworms (Note: Earthworms are not roundworms!)

  • Appeared ~400 million years ago (Still unclear – new research suggests much older)
  • Are the most numerically abundant animals on Earth (and could be the most diverse – estimates ranging from 10000 to 1 million species –  We really need to study them more…)

Additional info

Figure 2: Roundworm example

A: Evolution of Body Plan

1. Pseudocoelom – Nematodes (roundworms) are a bridge between “lower” and “higher” invertebrates.
  • Lower – no coelom (body cavity)
  • Higher – Coelom (body cavity)
Figure 3: Cross section of a roundworm

A pseudocoelom is a space between the mesoderm and the endoderm (not a true cavity – a true coelom will have a space within the mesoderm, not between cell layers)

Figure 4: Comparing acoelomates and coelomates
2. Complete digestive system – One-way digestive system with a mouth and an anus. Simplest animal with this.
  • Food can be digested step-by-step (more efficient)
  • Waste removal does not interfere with eating.
Figure 5: Internal anatomy of a roundworm
3. Bilateral Symmetry (with cephalization – similar to what developed in flatworms)
Figure 6: Comparing animal body plan symmetry

B. Feeding and Excretion

From advancement above:

Complete digestive system – One-way digestive system with a mouth and an anus. Simplest animal with this.

  • Food can be digested step-by-step (more efficient)
  • Waste removal does not interfere with eating.

Just like flatworms – two feeding styles are present:

Free-living Roundworms

  • Carnivorous (feed on animals that are even smaller)or herbivorous (feeding on phytoplankton such as diatoms, algae and fungi)
  • Can have teeth or spear-like structure to spear and suck out fluids of prey.
  • Ex. P. pacificus or C. elegans (an important model organism!)

Parasitic Roundworms

    • Get nutrients from a host – use one-way digestive system just like free-living roundworms.
    • Many different methods of attachment/feeding – ex. Hookworms have cutting plates that grab onto the intestinal lining.
Figure 7: Hookworm under an electron microscope (eyes added in MS paint for effect)
    • Can be parasitic to humans, plants, or animals.
Figure 8: Examples of parasitic roundworms

Excretion

  • Excretory tubes transfer solid waste to anus.
  • Waste (ammonia) is excreted through body wall with no associated organ.

C. Respiration and Circulation

No specialized organs for circulation and respiration (still nothing exciting…)

  • Gas exchange occurs through diffusion (O2 in, CO2 out) through the skin.

D. Reproduction

Sexual Reproduction

  • Most roundworms have two sexes (MOST ARE NO LONGER HERMAPHRODITES!)- male and female.
  • Internal fertilization within the female body
Figure 9: Comparison of sexes within the Ascaris genus
  • Males are smaller with spicule that open the vulva of females for sperm transfer.
Figure 10: Comparison of sexes in Ascaris genus – Spicule labelled

  • Although some are hermaphrodites that self-fertilize

Attack of the parasites!

For the final part of the webquest lets get you moving! Please choose 3 parasitic nematodes to learn about. There are information posters scattered around the class. You are expected to know the basics: name of worm, disease caused and symptoms, and life cycle (basic). You will eventually choose of these for a research project focusing on the science behind and global cooperation for management of the disease.