Flatworms

What are the main characteristics of flatworms?

Bilateral symmetry, dorsoventrally flattened bodies, three tissue layers, and some cephalization.

What does dorsoventrally flattened mean?

Flattened from top to bottom.

What is cephalization?

The concentration of nervous tissue at the anterior end (head region).

How many classes of flatworms are discussed?

Turbellaria, Trematoda, and Cestoda.

Are turbellarians free-living or parasitic?

Mostly free-living.

Where are planaria commonly found?

Cool, slow-moving streams.

What is the function of the ventral pharynx in planaria

Ingests food into the gastrovascular cavity.

What is the gastrovascular cavity in planaria?

A branching digestive cavity that distributes nutrients.

How are nutrients moved throughout a planarian’s body?

By diffusion and body movement.

What allows planaria to glide through water?

Cilia on ectodermal cells.

What is ciliated gliding?

Swimming using cilia.

What tissue allows planaria to twist and contract?

Mesodermal muscles.

What are eyespots in planaria?

Light-detecting structures.

: Can planarian eyespots form images?

No, they only detect light.

What is a ganglion?

A cluster of nerve cells.

Why is the ganglion in planaria considered a primitive brain?

Because it is concentrated in the anterior region and controls responses.

What type of nervous system do planaria have?

Ladder-like nervous system.

Why is it called a ladder-like nervous system?

Because of paired nerves connected by cross branches.

What are flame cells?

Ciliated excretory cells that remove wastes.

What nitrogenous waste do animals produce?

Ammonia (NH₃).

What are nephridiophores?

Tubes connected to flame cells.

What are nephridiopores?

Pores where wastes exit the body.

Why are flame cells called “flame cells”?

Their moving cilia resemble flickering flames.

Are planaria hermaphroditic?

Yes.

What does hermaphroditic mean?

Producing both sperm and ova.

How do planaria reproduce sexually?

Sperm are released into water, fertilization occurs, embryos develop into larvae, then adults.

What are trematodes commonly called?

Flukes.

Are flukes parasitic or free-living?

Parasitic.

What are the two major effects of parasitism?

Reduced need for digestion and increased reproductive specialization.

What is a primary host?

The organism where the adult parasite lives.

What is a secondary host?

An organism infected by larval stages.

Where do adult liver flukes live?

In vertebrate intestines.

: How do liver fluke eggs leave the host?

Through feces.

What secondary host commonly becomes infected by liver flukes?

Snails.

How do fluke larvae infect new hosts?

By burrowing through the skin.

What is polymorphism in flukes?

Different body forms during the life cycle.

Why were liver and blood flukes major human health problems?

Poor sanitation allowed larvae to infect humans through water or soil.

What are cestodes commonly called?

Tapeworms.

Why do tapeworms technically not have a head?

They lack concentrated nerve tissue or ganglia.

What is the scolex?

The attachment structure with hooks and suckers.

What is the function of the scolex?

Attaches the tapeworm to intestinal walls.

What are proglottids?

Reproductive body segments containing male and female organs.

What happens to proglottids as they age?

heir reproductive organs mature.

How do tapeworms obtain nutrients?

By absorbing nutrients from the host.

Can tapeworms grow very long?

es, several meters long.

Difference between Turbellaria and Trematoda/Cestoda?

Turbellaria are mostly free-living; Trematoda and Cestoda are parasitic.

Difference between flukes and tapeworms?

Flukes have complex life cycles with multiple hosts; tapeworms have scolexes and proglottids.

What structure is unique to tapeworms?

Scolex and proglottids.

What structure is unique to planaria?

Ladder-like nervous system and flame cells.