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