Phylum Nematoda

The Roundworms

Characteristics

• 12,000 species named• Live everywhere• Often parasites• Pseudocoelomates• Cylindrical shape• Most less than 5 cm• Can be microscopic to

1 meter in length

More Characteristics• Nonliving (noncellular) cuticle• Longitudinal muscles only • No circular muscles• Alimentary canal: mouth to anus• Important in decomposition and soil nutrients

Classification

C la ss R h ab d itea C la ss E no p lea

P h ylum N e m ato daT h e R o u n dw o rm s

Major Parasites

• Ascaris

• Hookworm

• Pinworm

• Trichina

• Whipworm

• Filarial worms

Ascaris

• An intestinal roundworm

• Common infection in horses, humans, and pigs.

• May lay 200,000 eggs per day

• Abdominal symptoms

Hookworm

• Curved anterior resembles a hook

• Hook to intestines• Causes anemia in

patient• Found in soil, burrow

through skin, most commonly foot

Hookworm

Hookworm eggsHookworm larvae

Pinworm

• Most common parasite in the United States

• Lives in large intestine and cecum.

• Females lay eggs in anal area at night

• Eggs develop within 6 hours, resulting in itching. If swallowed, mature in large intestine

Pinworm egg

Trichina

• Produces trichinosis• Adult worms burrow

in small intestine and produce live young

• Juveniles enter blood vessels and are carried to muscles

Whipworm

• Common in North America in humans

• Intestinal infection• Occurs through

contaminated food or unhygienic habits

Filarial Worms

• At least 8 species that infect humans

• Includes Elephantiasis, river blindness, dog heartworm

• Worms live in the lymphatic system

• Carried by mosquitoes

Dog Heartworm