Figure 10.24

Class Trematoda Parasitic flatworms called “flukes” All adult flukes are parasites of vertebrates

(live in mouth, skin, or gills of host) Outer body lacks cilia; tegument: has a

layer of glycoproteins that are important in protection against the host’s immune system.

Types of Hosts Most have complex life that alternates

between asexual and sexual stages Most require at least 2 different types of

hosts to complete their life cycle (most complex in all animal kingdom)!!

Primary host: the host in which a parasite reproduces sexually

Intermediate host: the host in which asexual reproduction occurs

Adhesive Organs

Oral sucker: anterior sucker that surrounds the mouth (attaches to host organs)

Acetabulum: below the oral sucker on the middle portion of the body (attaches to host tissue)

Opisthaptor – Extremely strong

adhesion

Important Parasites of Human Chinese Liver Fluke

Common parasite in Asia Over 30 million infected

Adult lives in bile duct of the liver feeding on epithelial tissue & blood

Embryonated eggs are released into the common bile duct

Eggs make their way to intestines to be eliminated in feces

Snail ingests eggs Emerges in waters Enters epidermis of fish that make contact Human eats raw or poorly cooked meat

Important Parasites of Human Sheep Liver Fluke

Common in sheep-raising areas Adult lives in bile duct of the liver feeding on epithelial

tissue & blood Embryonated eggs are released into the common bile

duct Eggs make their way to intestines to be eliminated in

feces Eggs hatch in freshwater and locate proper species of

snail. Encysts aquatic vegetation Sheep graze on vegetation & become infected Humans infected by eating watercress

http://animal.discovery.com/videos/monsters-inside-me-the-lung-fluke.html

Schistosome Fluke “Schistosomiasis” Common in Africa, S. &

Central America & S.E. Asia Over 200 million infected Decays liver, lungs, spleen

or intestines Female fluke lays eggs in

intestines or bladder of human. Egg secretions weaken walls

causing blood vessels to rupture; eggs leave the body.

If reach freshwater, eggs hatch into ciliated free-swimming larvae.

Schistosome Fluke “Schistosomiasis”

Burrows into aquatic snail tissue further developing. Leave snail to swim about.

Attach to human skin that comes in contact releasing tissue-degrading enzymes.

Larvae enter body and migrate to circulatory system. Cycle begins over.

http://animal.discovery.com/videos/monsters-inside-me-the-schistosomiasis-parasite.html

Class Cestoidea

Tapeworms Long, flat, parasitic Live in intestines Range from 1 mm to 25 cm!! Lack a mouth & digestive

tract; absorb nutrients across body wall

Cestoidea

Anterior region is called a scolex; often armed with circular suckers and hooks called rostellum

Cestoidea

Extending from the neck is a series of individual segments called proglottids; contain the sex organs and eggs.

Each segment is a reproductive sack and as it ripens it breaks off and exits host through the feces; full of eggs.

Cestoidea

http://animal.discovery.com/videos/monsters-inside-me-pork-tapeworm.html

Sometimes, dormant, protective cyst is formed in the intermediate host muscles.*** This is why you should never eat incompletely cooked meat!!

Beef Tapeworm Weight loss, chronic indegestion, diaherrea Adults live in small intestines Reach lengths up to 25 meters About 80,000 eggs per proglottid break free Eggs develop into six-hooked larva

(oncosphere) Cattle graze pastures contaminated with

human feces Ingest oncospheres

Beef Tapeworm

Cattle’s digestive enzymes free oncospheres. Larvae bore through intestinal wall into bloodstream using hooks

Bloodstream carries larvae to skeletal muscles, where they encyst and form a fluid-filled bladder

Human eats infected, raw or improperly cooked meat

Scolex attaches to intestinal wall and tapeworm matures

That is why it is important to cook your hamburger all the way through. If not you could end up with a full fledged T. saginata living inside of you, and they can grow over a meter long.

This is a scanning electron micrograph of the scolex (i.e., anterior attachment organ) of Rhinebothrium sp., a tapeworm in the new order Rhinebothriidea. The scolex is about 900 µm wide. This species, like all rhinebothriideans, has 4 bothridia on it scolex, each borne on a muscular stalk. Credit: Claire J. Healy

Additional Pictures

http://www.scuba-equipment-usa.com/marine/AUG04/Blue_Flatworm(Cycloporus_sp).html

Blue Flatworm(Cycloporus sp) http://www.scuba-equipment-usa.com/marine/AUG04/Hancock_Flatworm(Pseudobiceros_hancockanus).htmlHancock Flatworm(Pseudobiceros

hancockanus)

http://cas.bellarmine.edu/tietjen/images/platyhelminthes.htm