Phylum: Nematoda

• “thread-like”, commonly called roundworms, found just about everywhere

• Examples: ascaris, pinworms, hookworms, trichina worms

Traits

• Round bodies

Traits

• Non-segmented

Traits

• Bilateral symmetry

Traits

• cephalized

Traits

• Tube-in-a-tube (complete) digestive system – 2 openings

Traits

• Longitudinal muscles only

Traits

• Flame cells

Advantages of a complete digestive system

• Can eat continuously• Can eliminate wastes without losing good food

Why are worms so long?

• Since they have a straight G.I. tract, they must be long in order to have a tract long enough to digest and absorb food before it reaches the anus

Excretory system

• Flame cells collect waste and force them out through a series of tubes with one common exit

Reproduction

• Most are dioecious

Two categories:

Free living

Parasitic

Freeliving

• More abundant than the parasitic nematodes• Live in soil and water (fresh and salt)

Freeliving Nematodes

• Bacterial feeders• Fungal feeders• Many are beneficial in

helping to control disease and cycle nutrients in the soils

Size = average 1 mm in length

• Larger one consuming smaller parasitic ones

Plant parasitic nematodes

• Form cysts on the roots

Parasites

• Live in another organism

A few main types…

Ascaris Pinworms

Trichina wormsHookworms

Filarial worms

Ascaris

Ascaris

• Studied a lot because they are big and cheap

Ascaris life cycle

• Adults live in pig intestines, mate, eggs leave with feces

• Pigs ingest contaminated food or water, start over

• Since the cycle is simple, it’s hard to break

Ascaris larvae

Ascaris

Mouth

Ascaris in Pig Intestines

Pinworms

Pin worms

• Most common nematode parasite in humans

Pin worm life cycle

• Adults live in human intestines, mate, females crawl out the anus and lay eggs on the surrounding skin

• Kid scratches self, then eats without washing hands, starts over

Pinworm in Colon

Cure • Easy, oral medicine goes directly to them and

are flushed out with feces

Prevention

• Wash hands, especially after using the bathroom

Hookworms

Hook worms

• Intestinal parasites of humans, suck blood

Hook worm life cycle

• Adults live in intestines, mate, eggs leave with feces

• Hatch into larvae which bore through bare feet and eventually enter the lungs

• Crawl up trachea, are swallowed, start over

Hookworm larvae tracks

Symptoms

• Abdominal pain, severe diarrhea, anemia

Prevention

• Wear shoes• good sewage system

Trichina worms

Trichina worms

• Cause trichinosis, can be fatal

Red swollen eyesFatigue and diarrheaBrain swellingHeart failure

Trichina worm life cycle

• Adults live in pigs intestines, mate, eggs immediately hatch into larvae which bore through intestines into blood stream

• Eventually lodge and form cysts in the muscles, another animal eats it, start over

Meat infested with Trichina worm

Prevention

• Cook meat well• Inspect meat• Don’t feed pigs raw meat

Filarial worms

Filarial worms

• Cause elephantitis by clogging lymph nodes so they can’t drain fluids from the limb

Filarial worm life cycle

• Live and mate in fluids of body tissues, larvae are sucked out by mosquitoes and injected into another animal

Prevention

• Kill mosquitoes