01/04/2013
Nematodes:
Unsegmented Round Worms
Characteristics
• Simplest organism to have a ONE WAY DIGESTIVE
TRACT.
– True gut! (Not blind gut!)
– Mouth and anus are separate!
We know this is an advantageous step
because all more complex animals use this
one-way digestive tract.
Why is this so advantageous?
Characteristics
• Simplest organism to have a ONE WAY
DIGESTIVE TRACT.
– True gut! (Not blind gut!)
– Mouth and anus are separate!
• Round bodies
• Separate sexes and sexual reproduction
– Everything has been hermaphroditic up to now
(had the option of being either male or female)
Why is this advantageous?
Does it have any disadvantages?
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01/04/2013
Characteristics
• Simplest organism to have a ONE WAY
DIGESTIVE TRACT.
– True gut! (Not blind gut!)
– Mouth and anus are separate!
• Round bodies
• Separate sexes and sexual reproduction
– Everything has been hermaphroditic up to now
(had the option of being either male or female)
• Can be free-living or parasitic
Nematodes: Unsegmented Round Worms
Respiration: Diffusion through tissues and cuticle (skin)
Feeding: One-way digestive tract (simplified version of
the one we have) with mouth, pharynx, intestine, anus
Reproduction: sexual; most species have separate sexes
Movement: long muscles in cuticle contract
Internal transport: Diffusion through tissues
Response: simple chemoreceptors, ganglia
Excretion: Diffusion through tissues and cuticle
Why it’s important to know a bit about
nematodes:
• They are the most numerous of the
multicellular animals.
• They are extremely important to soil health
and soil food chains all over the world.
• They have been VERY successful as parasites.
– Video: Guinea Worm Disease
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01/04/2013
Roundworms and Diseases: Trichinosis
Trichinosis: caused by the trichinella worm
1. cysts within muscles of infected host are
consumed (usually by eating undercooked food)
2. worm grows in intestine of new host
3. worm forms cysts in the
muscles of the new host
(symptom: terrible pain
in muscles)
Roundworms and Diseases: Filarial Worms
Filarial Worms: occurs in
tropical Asian areas
• causes elephantiasis
• transmitted by
mosquitoes
Roundworms and Diseases: Ascarid Worm
Ascarid Worms: species of common roundworm
• Lives in intestine: eggs passed out in host’s feces
• most infect dogs, but some infect humans
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01/04/2013
Roundworms and Diseases: Ascarid Worm
Ascarid Worms: species of common roundworm
• Life cycle:
1. Food/water contaminated with eggs is
consumed by host.
2. Eggs hatch in small intestine of host.
3. Larve bore through intestinal wall, enter
bloodstream, and are carried to lungs
4. Larvae mature to adults in lungs, climb up
windpipe to throat, then are swallowed
5. Adult worms live in intestine and lay eggs that
leave host in feces.
Roundworms and Diseases: Hookworms
Hookworms: live in intestines
• burrows into the skin from soil
• matures in the intestines, using hooks to attach and
suck blood
Roundworms and Research: C. elegans
Caenorhabditis elegans: a model organism
• simple, free-living, about 1 mm long
• fixed number of cells: you
can track its cell division
history completely
• first organism to have its
DNA completely sequenced
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