Phylum Nematoda
Round Worms
General Characteristics
• 16,000 species–3 major classes
• Very numerous–5 billion in 1 acre of garden soil
• Triploblastic–Ectoderm, Mesoderm,
Endoderm• Pseudocoelomates• Bilaterally symmetrical• Un-segmented
• Body Description:–Body is round with
tapered ends–Excretory system–Body wall w/
longitudinal muscles
Body Description Cont.
• Separate mouth and anus! Success!
Taxonomy– Parasites and free-living– Ex: pinworms, hookworms,
filarial
– Mostly free living, few parasite species
– Ex: Trichinella
Pinworm
Hookworm
Body Plan
Pseudocoelom- body cavity is lined on only 1 side by mesoderm.–Serves as a
hydrostatic skeleton
Body Systems• Digestive:
–Varies depending on the type of Nematode
–Complete digestive tract: pharynx, intestine, rectum and anus.•Can be carnivorous, herbivorous, omnivorous, or saprotrophic (decomposer)
Excretory Systems• gland cells that function in excretion• Glandular system- renettes absorb
waste and empty it outside the body.• Tubular system- renettes all empty
into a common canal. The waste is then excreted together through an excretory pore.
Reproduction
• Mostly dioecious (2 separate sexes)–Internal fertilization–Reproduction is Sexual
Ascarid Worms (common
roundworm)
- lives in intestine
- eggs are passed out in the fecesMost roundworms infect
dogs, but occasionally
they find their way into
human hosts
Pinworm• Intestinal parasite• 8-13 mm in length (size of a staple)• Most common parasitic roundworm in the US• Affects mostly school age children• Spread by ingesting eggs that are on the
fingernails• Travel through the digestive tract• Female pinworms emerge from the anus at night
to lay eggs
Pinworms
Hookworm
• 10-13 mm in length
• Transmitted by walking barefoot on soil contaminated by feces, and fertilizer made by human feces
• Causes anemia
Hookworms
- burrow into the skin from soil
- mature in the intestines
--hooks used to attach and suck blood
Hookworm
Filarial Worms
• Cause the disease elephantiasis
• Tropical disease affecting over 170 million people
• Affects the lymphatic system
• Transmitted by mosquito bites
Filarial Worms - found in Tropical regions of
Asia
Filariasis (Elephantiasis)
Roundworms & Disease
Trichinosis
(trichinella worm)
- cysts within the muscles are
consumed (undercooked
food)
-- worm grows in intestine
-- forms cysts in the muscles
of the new host
-- symptom: terrible pain in
muscles
Research on C. elegans●first organism to have DNA completely
sequenced●It is a very simple, free living roundworm