Parasitology Lec 7: Platyhelminthes- Flatworms

What is the topic of Lecture 7?

Platyhelminthes: Flatworms.

What embryonic tissue condition do Platyhelminthes have?

Triploblastic.

What body-cavity condition do Platyhelminthes have?

Acoelomate.

What developmental condition do Platyhelminthes have?

Protostomes.

What are protonephridia?

Osmoregulatory and excretory organs closed at the inner end.

What do protonephridia contain?

Flame cells.

What do the beating flagella of flame cells do?

Drive fluid down the tubule.

Where does most ammonia excretion occur in Platyhelminthes?

Across the body wall.

What symmetry do Platyhelminthes have?

Bilateral symmetry.

What nervous-system trend do Platyhelminthes have?

Cephalization.

How do most Platyhelminthes reproduce sexually?

Most are hermaphroditic (monoecious).

What type of fertilization occurs in most hermaphroditic Platyhelminthes?

Cross fertilization.

What additional type of fertilization occurs in Platyhelminthes?

Internal fertilization.

What is the topic of the next section?

Class Turbellaria.

What type of flatworms are most Turbellarians?

Mostly free-living flatworms.

What habitats do Turbellarians occupy?

Marine, freshwater, and terrestrial.

What feeding roles do Turbellarians have?

Most are predators; some are scavengers.

What covers Turbellarians?

A ciliated epidermis.

What sensory devices do Turbellarians have?

Eyespots and auricles.

What are eyespots?

Light sensitive.

How are Turbellarians phototactic?

Negatively phototactic.

What are auricles?

Sensory lobes on the head used for chemoreception.

What is the topic of the next section?

Class Monogenea.

What covers the body of an adult Monogenean?

A syncytial tegument without cilia.

Where do most Monogeneans parasitize?

The skin or gills of fish.

Where do a few Monogeneans parasitize?

The urinary bladder of frogs and turtles.

What unusual host does one Monogenean parasitize?

The eye of a hippopotamus.

How host-specific are Monogeneans?

They are very host specific.

How do Monogeneans mainly attach to the host?

By means of a haptor.

What is a haptor?

A posterior attachment organ that contains suckers and hooks.

What other structure helps with attachment in Monogeneans?

An oral sucker.

How many hosts do Monogeneans need?

Only one host.

What type of host do Monogeneans not need?

An intermediate host.

Where is sexual maturity reached in Monogeneans?

In or on a fish.

What is produced after Monogeneans reach sexual maturity?

Eggs.

What do Monogenean eggs hatch to produce?

A ciliated larva called an oncomiracidium.

What happens when an oncomiracidium attaches to a fish?

It becomes an adult.

What is the common name for Class Trematoda?

Flukes.

Why are trematodes important?

Economically and medically important.

What are almost all adult trematodes?

Endoparasites of vertebrates.

What attachment structures do trematodes have?

One or more suckers, usually oral and ventral suckers.

What attachment structure do trematodes not have?

Hooks.

What covers the body of an adult trematode?

A syncytial tegument without cilia.

What does syncytial mean?

Many nuclei enclosed within a single cell membrane.

What protection does a syncytial tegument offer?

Protection against the host.

What else does a syncytial tegument increase?

Gas exchange.

What type of digestive tract do trematodes have?

A mouth opening and a blind-ended digestive tract.

What does the parasite ingest through its mouth?

The host's blood.

What does Digenea mean?

Two births.

How many intermediate hosts do Digeneans have?

At least one intermediate host.

What is the first intermediate host of a Digenean?

A mollusc, such as a snail.

How many intermediate hosts do some Digenean species have?

Second and third intermediate hosts.

What is a definitive host?

The host in which sexual reproduction occurs.

What type of organism is the definitive host?

A vertebrate.

How does the shelled embryo or larva leave the definitive host?

In excreted waste.

What must the shelled embryo or larva reach to develop further?

Water.

How does host location occur?

It is an active process mediated by highly specialized, free-living larval stages.

What does a fertilized Digenean egg give rise to?

A single, free-living miracidium larva.

What must a miracidium enter to develop further?

A mollusc, most often a snail.

How does a miracidium enter a snail in some species?

It is eaten by the snail.

How does a miracidium enter a snail in other species?

It bores into the snail.

What does a miracidium become once inside the snail?

It dedifferentiates into a sporocyst stage.

Where does the sporocyst live?

In the molluscan blood circulatory system (hemocoel).

How does a sporocyst grow?

It has no mouth and must grow by taking up dissolved nutrients.

What develops within the sporocyst?

Germ balls.

What does each germ ball develop into?

A redia, another larval stage.

Where do rediae migrate?

To the snail's digestive gland or gonad.

How do rediae feed?

They are active feeders with a functional mouth.