Phylum Nematoda (roundworms)

• 12,000 spp.• free-living & parasitic• ubiquitous• important in medicine and horticulture

Morphology• slender, elongate, & most <2.5mm• cuticle containing collagen• longitudinal muscles only - producing

eel-like undulations• circumpharyngeal nerve ring and

longitudinal nerve cords

Reproduction & Development

• dioecious• hermaphrodites• egg storage in the uterus• may produce 200,000 eggs/day• protostomes

Ascaris (egg and juvenile)

Ascaris (female dissection)

Enterobius - “pinworm”• 16% adults & 30 %

children in US are infected

• female deposits eggs at night in the perianal region

• complex life cycle

Enterobius- male & female

Enterobius (female)

Necator – “hook worm”• mouth parts are designed

to bite onto the lining of the intestine, abrade the surface and suck the patients blood.

• many people show no outward symptoms of disease.

• the severity of the disease depends on the number of worms per individual, the nutritional state of the patient and the species of hookworm

Necator

Trichinella• causes trichinosis

• acquired by eating undercooked pork

• larvae encyst in host muscle tissue

Dirofilaria – dog heart worm

Wuchereria – causes elephantiasis

• afflicts ~ 100 million and is said to be one of the world’s fastest spreading diseases

• the parasite clogs the lymph vessels of the host.

Dracunculus