Phylum Nematoda The Roundworms

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Phylum Nematoda The Roundworms thread like
www.onacd.ca
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Identifying Characteristics of Nematodes

• Pseudocoelomate which allows them to have a
  complete ONE WAY digestive tube (separate mouth
  and anus but no muscles!)
• Exhibit cephalization with a ventral nerve cord
• No respiratory or circulatory system present
• Developed reproductive system and excrete wastes
  through a pore
• Sexes are separate (dioecious) and use sexual
  reproduction
• Bodies are unsegmented and they are born with a
  certain number of cells that increase in size as
  they grow
• Their epidermis secretes a cuticle made of
  collagen to keep it from drying out and this
  cuticle molts as the worm grows
• Possess only longitudinal muscles
• Contains many parasitic and free-living forms
  found in fertile soil

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Parasitic Species of Nematodes include
WHIPWORMS which invade the human large intestine.
Are responsible for the disease Trichinosis
HOOKWORMS which invade the small intestine of
dogs, cats and humans. They cause anemia as they
suck blood voraciously
PINWORMS which invade the upper parts of the
colon. Males are 1-4mm and females are 8-13 mm
in length. FILARIDS which invade many different
parts of the body are responsible for a range of
diseases (incl. elephantiasis and Loa Loa)
ASCARIDS which invade the human intestine and are
responsible for the disease Ascariasis
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AscariasisCaused by Ascaris lumbricoides

• Ascaris infection is prevalent in tropical
  regions with poor hygiene
• Host becomes infected by ingestion of food
  contaminated with fecal matter containing eggs
• Diagnosis is usually made when the worms are
  passed through stool or vomit
• Upon autopsy, a 2 year old South African girl was
  found to have 796 worms in her ileum

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Life cycle of Ascaris lumbricoides

• Upon ingestion of the eggs the larvae hatch,
  burrow through the intestine, reach the lungs and
  then migrate up the respiratory tract
• The larvae are then re-swallowed and mature in
  the intestine grow up to 30 cm in length
• Larvae anchor themselves to the intestinal wall
• See next slide for detailed life cycle

Ascaris larva developing inside egg
Larvae exiting egg
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• 1. Adult worms live small intestine. A female
  may produce approximately 200,000 eggs per day,
  which are passed with the feces
• 2-3. Fertilized eggs develop embryos and become
  infective after 18 days to several weeks after
  ingested depending on the environmental
  conditions
• 4-5. The larvae hatch invade the intestinal
  walls and travel via the circulatory system to
  the lungs .

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6. The larvae mature further in the lungs (10
to 14 days and then migrate to the throat, and
are swallowed 7. Upon reaching the small
intestine, they develop into adult worms 8.
Between 2 and 3 months are required from
ingestion of the infective eggs to oviposition by
the adult female. Adult worms can live 1 to 2
years.
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Elephantiasis

• Elephantiasis is a disease characterized by a
  thickening of the skin and underlying tissues
  which can be caused by invasion of the lymph
  nodes by nematodes
• Nematodes are transmitted by mosquitoes that
  mature and lodge themselves in the lymph nodes of
  the host
• Affects the legs and genitals
• More prevalent in tropical climates with over 120
  million people affected worldwide

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Ecological Roles of Free-living Nematodes

• Are decomposers they recycle bacteria, fungi
  and decaying, rotting organic matter back into
  the soil.
• This means they are very important to the
  chain of energy production and matter recycling
  of the earth.

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Negative Effects of Parasitic Nematodes

• Parasitic Nematodes
• Invade many different types of crops and often
  cause crop death
• Attack the bark of forest trees (pine wood
  nematode)
• Invade the intestine of many mammals and cause
  sickness and often eventual death if untreated.

Soybean Cyst nematode infects soybean plant
crops and causes cysts on the plants
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• If all the matter in the universe except the
  nematodes were swept away, our world would still
  be dimly recognizable, and if, as disembodied
  spirits, we could then investigate it, we should
  find its mountains, hills, vales, rivers, lakes
  and oceans represented by a thin film of
  nematodes. The location of towns would be
  decipherable, since for every massing of human
  beings there would be a corresponding massing of
  certain nematodes. Trees would still stand in
  ghostly rows representing our streets and
  highways. The location of the various plants and
  animals would still be decipherable, and, had we
  sufficient knowledge, in many cases even their
  species could be determined by an examination of
  their erstwhile nematode parasites. 
• N.A.Cobb (United States Department of
  Agriculture, 1914)