Phylum Nematoda•Parasites and free-living•Lack cilia except in their sensory structures

•Marine, freshwater, and soil habitats

•Triploblastic, bilaterally symmetrical•Unsegmented vermiform (wormlike organism)

Phylum NematodaExternal features

•Noncellular, collagenous cuticle

• Can molt 4 times during maturation

• Maintains internal hydrostatic pressure

• Mechanical protection• Resists digestion by the host

Phylum Nematoda• Longitudinal muscles are used for

locomotion• Thrashing movements (can’t crawl like

worms)

Phylum Nematoda•Sensory organs

•Amphids – chemoreceptors along the cuticle

•Phasmids - chemoreceptors near the anus

•Ocelli – eyespots found in aquatic nematodes

Feeding and Digestive SystemCarnivores, herbivores, omnivores, saprobes(decomposers), or parasitic

Complete digestive systemmouth->buccal cavity->pharynx ->tubular intestine->rectum->anus

Hydrostatic pressure pushes food thru

Other Organ SystemsGlandular system

•Aquatic nematodes•Renettes – absorb nitrogenous waste

Tubular system•Parasitic nematodes•Renettes form a canal

Other Organ Systems

•Nervous system•Nerve ring from anterior to posterior

•Also have neuroendocrine secretions involved in growth, molting, cuticle formation, and metamorphisis

ReproductionSexual•Dioecious-having separate sexes

•Dimorphic-males are smaller than females

•internal fertilization

Reproduction•Males

•One testis•Bursa- used to insert their sperm into the female

•males have ameboid sperm

Reproduction•Females

•Pair of convoluted ovaries•Oviducts become uterus•Several hundred to several hundred- thousand eggs per day

•Ovovivparity – giving birth to larvae that hatched from an egg

Some Important Nematode Parasites of Humans

•Ascaris lumbricoides•Enterobius vermicularis•Necator americanus•Trichinella spiralis•Wuchereria bancrofti

Ascaris lumbricoidesThe Giant Intestinal Roundworm- The adult female worm can be over 30 cm long and 2-6 mm wide

800 million infected- most common parasitic worm disease in the world

Ascaris lumbricoidesAdults live in small intestines of

humansEggs exit with through feces Once the eggs are ingested, they

hatch in intestine and travel to the lungs

Larvae molt twice, they travel to the trachea where they are swallowed

Ascaris lumbricoidesWarning: those with weak stomachs need not

continue viewing. Only for the HBO audiences!

When Ascaris becomes a big problem. . .

Enterobius vermicularisPinwormMost common parasite in US

Adults live in large intestine

At night females migrate out of the anus and lay eggs on skin

Enterobius vermicularisHuman ingest eggs, hatch and molt 4 times in small intestine & migrate to large

Necator americanus•Found in Southern US•Adults live in small intestine with teeth and feed on blood & tissue fluid

•Females 10,000 eggs daily & pass out of body in feces

Necator americanus

Eggs hatch in warm moist soil and releases a small larva, the larva molts and becomes the infective filariform larva.

hookworms living in soil

Necator americanusHumans become infected when filariform penetrates the skin (usually b/w toes) to reach our circulatory system

Trichinella spiralisThe PorkwormAdults live in mucus of small intestine of humans and other mammals

Adult female Adult male

Trichinella spiralisFemales birth young, larvae enter circulatory system and are carried to Skeletal (striated) Muscles

Larvae entering into Skeletal Muscle cells

Trichinella spiralisLarvae encyst in muscles & remains infective for many years

Another host must ingest infective meat to continue the life cycle

Trichinella spiralisHumans become infected by eating improperly cooked pork products

Larvae encyst in stomach move to small intestine molt 4 times, turn into Adults

Wuchereria bancroftiThe Filarial wormsIn tropical countries over 250 million human infected

Wuchereria bancroftiThread-like worms that live in the Lymphatic System, block the vessels

This causes enlargement of various appendages: Elephantiasis

An Adult female Wuchereria bancrofti is about 80-100 mm long and 0.24-0.30 mm in diameter, whereas a male is about 40 mm long and 0.1 mm in diameter.

ElephantiasisWarning: Pictures not for everyone!

Wuchereria bancroftiAdults copulate produce microfilariae.

The microfilariae released into the blood stream

A microfilaria is about 240-300 µm (micrometers) long and 7.5-10 µm thick

Wuchereria bancroftiMosquito (intermediate host) feeds on human (definitive host) ingest microfilariae and larvae molts 2 times

Mosquito bites another human it injects 3rd stage larvae into human blood, molts, enters lymphatic system

Other Filarial WormsDirofilaria immitis in US parasite of dogs

Adult worms live in heart, large arteries, and lungs

Heartworm disease- fatal to dogs, unless give preventative medicine