Phylum: Nematoda
Phylum:
Nematoda
Nematodes
Origin of the word nematoda: Nema = greek for thread
Animals in this phylum include: A variety of free living and
parasitic round worms
Level of organization
-organ and organ systems
Type of Body Cavity
- Pseudocoelomate
Symmetry: Bilateral
Basic Nematode Body Plan
Germ Layer: ecto, endo and mesoderm
Body Plan
- Tube within a tube
Has 2 openings (mouth and anus)
= complete digestive tract
Pseudocoelomate
Open cavity allows for:
- Organ development
- Allows nutrients to flow
around the organs
- Acts as a skeletal structure
Skeletal structure
Hydrostatic skeleton:
(Think: water balloon)
Muscles act against the pressure of the fluid in
the body cavity.
Segmentation:
Nonsegmented: outer body is smooth
Compare and contrast
Platyhelminthes and nematodes share:
-Hermaphrodites
-Bilateral
Significant evolutionary changes found Nematodes:
- Complete digestive tract (2 openings)
- Pseudocoelom (open body cavity)
Parasitic Nematodes
Ascaris lumbricoides:
Length: 20-35 cm (female is larger than male)
Unlike other nematodes
Ascaris worms are
either male or female
Host: Humans and pigs
Anatomy of Ascaris
Ascaris Life cycle
Step in development
1) Eggs are found in soil, feces or vegetation
2) Eggs are ingested by host when host eats
contaminated soil, feces or vegetation
Ascaris Life cycle
Step in development
1) Eggs are found in soil, feces or vegetation
2) Eggs are ingested by host when host eats
contaminated soil, feces or vegetation
3) Once ingested egg reaches the small intestine it
hatches.
4) Juvenile worm moves into circulatory system
Ascaris Life cycle
Step in development
1) Eggs are found in soil, feces or vegetation
2) Eggs are ingested by host when host eats contaminated
soil, feces or vegetation
3) Once ingested egg reaches the small intestine it hatches.
4) Juvenile worm moves into circulatory system
5) Once in circulatory system it moves to heart and then
lungs
6) Juvenile moves into lungs travels up the trachea up to the
mouth.
Ascaris Life cycle
Step in development
1) Eggs are found in soil, feces or vegetation
2) Eggs are ingested by host when host eats contaminated
soil, feces or vegetation
3) Once ingested egg reaches the small intestine it hatches.
4) Juvenile worm moves into circulatory system
5) Once in circulatory system it moves to heart and then
lungs
6) Juvenile moves into lungs travels up the trachea up to the
mouth.
7) Once in the mouth it is swallowed by host where it moves
back down the esophagus past the stomach and back into
the small intestine
8) Once in the small intestine it feeds off hosts food and
matures into a reproductive adult
Parasitic Nematodes
Trichinella spiralis:
Length: ~2mm
Host: Human become infected when they eat
undercooked pork. Pork muscle may contain
encysted trichinella larvae.
Life cycle of trichinella
1) After exposure to gastric acid and pepsin, the larvae
are released from the cysts and invade the small
intestine where they develop into adult worms.
2) The life span in the small bowel is about four weeks.
Life cycle of trichinella
1) After exposure to gastric acid and pepsin, the larvae are
released from the cysts and invade the small intestine
where they develop into adult worms.
2) The life span in the small bowel is about four weeks.
3) After 1 week, the females release larvae that migrate to
striated muscles where they encyst (form a cacoon-like
structure)
Diagnosis: Based on clinical symptoms, and is confirmed by
serology (blood analysis) or identification of encysted or
non-encysted larvae in biopsy or autopsy specimens.
Assignment
Diagram the life cycle of Ascaris lumbricoides
Finish vocab: 629-635