Phylum: NematodaPhylum: Nematoda

NematodesOrigin of the word nematoda: Nema = greek for threadAnimals in this phylum include: A variety of free living and parasitic round worms Level of organization-organ and organ systemsType of Body Cavity- PseudocoelomateSymmetry: Bilateral

Basic Nematode Body PlanGerm Layer: ecto, endo and mesodermBody Plan- Tube within a tube Has 2 openings (mouth and anus) = complete digestive tract PseudocoelomateOpen 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 NematodesAscaris lumbricoides:Length: 20-35 cm (female is larger than male)Unlike other nematodesAscaris worms are either male or femaleHost: Humans and pigs

Anatomy of Ascaris

Ascaris Life cycleStep in development1) Eggs are found in soil, feces or vegetation2) Eggs are ingested by host when host eats

contaminated soil, feces or vegetation

Ascaris Life cycleStep in development1) Eggs are found in soil, feces or vegetation2) Eggs are ingested by host when host eats contaminated

soil, feces or vegetation3) Once ingested egg reaches the small intestine it hatches. 4) Juvenile worm moves into circulatory system

Ascaris Life cycleStep in development1) Eggs are found in soil, feces or vegetation2) Eggs are ingested by host when host eats contaminated

soil, feces or vegetation3) Once ingested egg reaches the small intestine it hatches. 4) Juvenile worm moves into circulatory system5) Once in circulatory system it moves to heart and then

lungs6) Juvenile moves into lungs travels up the trachea up to the

mouth.

Ascaris Life cycleStep in development1) Eggs are found in soil, feces or vegetation2) Eggs are ingested by host when host eats contaminated soil,

feces or vegetation3) Once ingested egg reaches the small intestine it hatches. 4) Juvenile worm moves into circulatory system5) Once in circulatory system it moves to heart and then lungs6) 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 NematodesTrichinella spiralis: Length: ~2mmHost: Human become infected when they eat

undercooked pork. Pork muscle may contain encysted trichinella larvae.

Life cycle of trichinella1) 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