Nematoda, Nematomorpha, Scalidophora OEB 51 Lab 7: Nematoda, Nematomorpha, Scalidophora

Lab 7: Nematoda, Nematomorpha, Scalidophora OEB 51 Lab 7: Nematoda, Nematomorpha, Scalidophora

30 March 2016

Nematoda These parasitic and free-living unsegmented worms are one of the most abundant animal groups and found in virtually every habitat on Earth. Their bodies are round in cross-section, covered with CHOOSE a cuticle and the body wall has only longitudinal muscles. ONE

• Turbatrix aceti (live, free-living) These ‘vinegar eels’ are found in cultures used in the production of vinegar. Observe them moving under the compound scope. What type of musculature do they use to move in this way? Can you see any changes in the diameter of the round body as it moves? What constrains body shape?

• Caenorhabditis elegans (live, free-living) This nematode is used as a model organism in developmental biology because it is free-living, easy to culture, matures in 3 days and has a fixed number of cells. Observe these animals in culture and then use a probe to transfer some to a slide. Draw an adult C. elegans and try to observe and label the following structures: pharynx, intestine, vulva, gonad containing oocytes, and tail. Tauana also has fluorescent specimens for demonstration (courtesy of OEB professor Yun Zhang).

- How many cells does C. elegans have in the body? How do you call this property of having a fixed number of somatic cells?

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• Parascaris zebrae (preserved from MCZ) Examine this parasitic nematode (found in the small intestine of a zebra). Use a forceps to hold the anterior part of the body and look down at the shape of the terminal mouth. Make a sketch and compare it to the free-living genera.

- All the animals we are looking at today are ecdysozoans. What feature of the group does the name refer to? Before this clade was discovered in molecular phylogenies, what was the paradigm in the animal tree?

2 Lab 7: Nematoda, Nematomorpha, Scalidophora OEB 51 Nematomorpha Adult nematomorphs are free living, but the larvae are parasitic on arthropods. Many adult horsehair worms only emerge from their hosts when they are near water, and they act on the host’s brain, driving water-seeking behavior and drowning of the host (e.g. the horrifying clip of the cricket jumping into a swimming pool). Check out this and more videos of adult nematomorphs emerging from their hosts!

• Gordius sp. • Paragordius sp.

We have several preserved specimens from the MCZ. Make a sketch (identify the genus) and pay close attention to the posterior end. Can you tell if it is a male or female? Can you see a cloacal pore?

- We have a “gordian knot” of worms. What might be the function of this behavior?

- Nematomorphs are sometimes called “horsehair worms” and “Gordian worms.” Where do these names come from? (After coming up with your own idea, check out page 362 of the old Brusca or page 686 of the new Brusca)

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Priapulida Scalidophora refers to structures called scalids; check them out in a textbook. What is the distinction between a scalid and a “normal” pharyngeal tooth?

• Priapulus caudatus (preserved in ethanol) – you should be able to readily distinguish introvert, trunk and caudal appendage. What might be the function of the caudal appendage? Can you see scalids on the introvert?

• Although there are priapulidans that look very different from Priapulus, you might have noticed how they resemble sipunculan annelids in external morphology. What characters readily distinguish one from the other?

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Kinorhyncha We have available three slides of kinorhynchs; use the space below to draw an entire organism. Can you see the introvert (or is it withdrawn)? How many segments do they have? What features unite this phylum with other Scalidophora? What is unique (synapomorphic) about kinorhynchs relative to the other scalidophoran phyla?