Chapter 9 part 4 worms

What are germ layers?

As the embryo develops, 3 germ layers form. They interact with each other and contribute to the formation of all tissues and organs.

What does the ectoderm form?

Ectoderm (outer layer):

• Brain & nervous system

• Epidermis of the skin

• Pituitary gland

• Lens of the eye

What does the endoderm form?

Endoderm (inner layer):

• Digestive system

• Respiratory system

What does the mesoderm form?

Mesoderm (middle layer):

• Muscles

• Skeleton

• Heart

• Blood

• Kidneys

• Reproductive system

Why are germ layers important?

They allow the formation of TRUE organ systems.

What is a coelom?

A coelom is a body cavity completely within the mesoderm.

What is a pseudocoelom?

A pseudocoelom is a body cavity between the mesoderm and endoderm.

Which worms have no coelom?

Flatworms (Platyhelminthes) – acoelomate

Which worms have a pseudocoelom?

Roundworms (Nematoda)

Which worms have a true coelom?

Earthworms (Annelida)

What does Platyhelminthes mean?

Platy = flat

Helminth = worm

What are flatworms thought to be descended from?

A type of early jellyfish

How many classes are in Phylum Platyhelminthes?

There are 3 classes.

What is Class Turbellaria?

Includes beautiful free-living marine worms and planarians

What are planarians?

• >3,000 free-living species

• A few parasitic forms

• Mostly aquatic, few on land

• Body adapted to a free-living lifestyle

What organisms are in Class Cestoda?

Tapeworms

Key traits of Cestoda

• >3,500 species

• Almost all intestinal parasites

• Highly specialized body and life cycle

What organisms are in Class Trematoda?

Flukes

Key traits of Trematoda

• >6,000 parasites

• Infect liver, lungs, blood, muscles

• Body & life cycle adapted to parasitic existence

What suckers do flukes have?

• Oral sucker

• Ventral sucker

What type of symmetry do flatworms have?

Flatworms demonstrate a bilaterally symmetrical body plan.

Do flatworms have a skeleton?

No, flatworms lack a skeleton.

Are flatworms coelomate, pseudocoelomate, or acoelomate?

Flatworms are acoelomate.

Why are flatworms flat?

Their flat shape allows simple gas exchange by diffusion through the skin.

How many species of flatworms are there?

About 20,000 species.

Where are flatworms found? (This is related to their food source)

They are found in many places and can be free-living scavengers or parasites.

What type of digestive cavity do flatworms have?

A highly branched gastrovascular cavity.

How many openings do flatworms have for digestion?

Only one opening, which functions as both mouth and anus.

How can flatworms cause skin irritation?

Some flatworms have stomach secretions that can irritate the skin.

How can flatworms transmit parasites?

Handling flatworms can transmit parasites.

What toxin do some flatworms have?

A neurotoxin called tetrodotoxin (like pufferfish).

How is tetrodotoxin dangerous?

It is dangerous if it enters the body through a cut or touches the eyes or mouth, as a Neurotoxin, it attacks the nervous system.

What important evolutionary trait do flatworms show?

They are the most primitive organisms to show cephalization.

What is found in the head region of flatworms?

A concentration of nerve tissue called ganglia (singular: ganglion).

What do ganglia resemble?

A primitive brain.

How many nerve cords do flatworms have?

They have two nerve cords

Where do the nerve cords run?

From the ganglia in the head, along the ventral side, to the tail region.

What do the nerve cords control?

They control muscles, allowing flatworms to move or eat.

How many types of stimuli can flatworms sense?

At least three forms of stimuli.

How do flatworms sense light?

Eye-spots detect light and allow flatworms to respond.

What can flatworm eye-spots distinguish?

They can only distinguish light from dark - still better than Cnidarians.

How do flatworms sense chemicals?

Pits on the sides of the head sense chemicals in the water (like smelling).

How do flatworms sense touch?

Auricles on either side of the head region sense touch.

Name three main features of a planarian head

• Eyespots (light sensors)

• Auricles (touch sensors)

• Ganglia (primitive brain)

What structure connects the mouth to the gastrovascular system in flatworms?

The long muscular pharynx.

Do flatworms have separate mouth and anus?

No. Flatworms have a mouth/anus (called a proctostome).

What system is the mouth/anus connected to?

The gastrovascular system.

What structure connects the mouth/anus to the gastrovascular system?

A long muscular pharynx.

What do flatworms eat?

Bacteria, plankton, or remains of dead animals found in lakes and streams.

How is food taken into the flatworm’s body?

Food is taken into the mouth/anus by the muscular pharynx.

Where is food digested in flatworms?

In the highly branched gastrovascular cavity.

How do nutrients move to body cells?

Nutrients move from the gut into body cells by diffusion.

How does respiration occur in flatworms?

Respiration occurs by diffusion

How do oxygen and nutrients enter body cells?

They are absorbed directly into body cells by diffusion.

How is undigested food removed from flatworms?

Most undigested food is released directly out of the mouth/anus.

What is a flame cell?

A specialized excretory cell.

What do flame cells do?

They function like a kidney, removing waste materials.

Why are flame cells called “flame cells”?

The beating of cilia resembles a flame.

How do flatworms move across surfaces?

By using cilia on their ventral surface.

What muscles help flatworms move?

Circular and longitudinal muscles just below the ectoderm.

What controls flatworm muscles?

The nerve cords.

Are flatworms male or female?

Flatworms are hermaphroditic.

What does hermaphroditic mean?

They can produce eggs and sperm within the same body.

Is self-fertilization common in flatworms?

No, self-fertilization is extremely uncommon.

How else can flatworms reproduce sexually?

Through physical contact between two flatworms, where sperm from one is absorbed into the skin of another.

What class of flatworms includes planarians?

Class Turbellaria (Planarians)

What type of symmetry do flatworms have?

Bilateral symmetry

Do flatworms have a skeleton?

No, they lack a skeleton

What does acoelomate mean in flatworms?

They lack a body cavity

Why can flatworms exchange gases easily?

They are flat, allowing gas exchange by diffusion through their skin

How many species of flatworms are there approximately?

About 20,000 species

Where are flatworms found?

In many places; they can be free-living scavengers or parasites

What type of digestive system do flatworms have?

A highly branched gastrovascular cavity

How many openings does the flatworm digestive system have?

One opening that serves as both mouth and anus

What is the function of the gastrovascular cavity?

Digestion and distribution of nutrients

Why can flatworms cause skin irritation?

Some have stomach secretions that irritate the skin

How can parasites be transmitted by flatworms?

By handling flatworms

What neurotoxin do some flatworms have?

Tetrodotoxin

Why is tetrodotoxin dangerous?

It can enter through cuts or touch eyes or mo

What is cephalization?

Concentration of sensory and nerve tissue at the head

Why are flatworms considered primitive in cephalization?

They are the simplest organisms to show it

What are ganglia?

Concentrations of nerve tissue resembling a primitive brain

Where are ganglia located in flatworms?

In the head region

How many nerve cords do flatworms have?

Two ventral nerve cords

What do the nerve cords control?

Muscles that allow movement and feeding

How many types of stimuli can flatworms sense?

At least three

How do flatworms sense light?

Through eyespots

What can eyespots distinguish?

Light vs. dark

How do flatworms sense chemicals?

Pits on the side of the head sense chemicals in water

How do flatworms sense touch?

Through auricles on the head region

Are flatworms protostomes or deuterostomes?

Protostomes

What structure connects the mouth to the gastrovascular system?

A muscular pharynx

What do flatworms eat?

Bacteria, plankton, or remains of dead animals

How does respiration occur in flatworms?

By diffusion

How do nutrients move to body cells?

By diffusion from the gut

How is undigested food released in flatworms?

Directly out of the mouth/anus

What is a flame cell?

A specialized excretory cell

What is the function of flame cells?

Remove waste materials (kidney-like function)

How do flatworms move across surfaces?

Using cilia on their ventral surface

What muscles aid flatworm movement?

Circular and longitudinal muscles