Phylum Platyhelminthes and other Acoelomate Animals, Chapter 8, Zoology - PowerPoint Presentation

Slide1

Phylum Platyhelminthes and other Acoelomate Animals, Chapter 8, Zoology

Slide2

Characteristics of Phylum Platyhelminthes (means “flat worm”)

Flatworms have

three germ layers (

triploblastic

); they are the first animal we have discussed in this class with

true organs and tissues

.

Bilateral symmetry

and

cephalization

.

Flatworms are

acoelomate

, which means the

spaces between the organs

are

filled with mesoderm tissue

called

parenchyma.

Slide3

Characteristics of Phylum Platyhelminthes (means “flat worm”)

The nervous system

in flatworms consists

of

anterior

organs

called

ganglia

that

form

a simple brain

.

Excretory system

consists of

two lateral canals connected to structures

called

flame

cells.

They have

no

circulatory or respiratory organs

;

respiration occurs by

simple diffusion.

Slide4

Ecology of Flatworms (Platyhelminthes)

Many flatworms

like the

turbellarians

are

free-living

(meaning non-parasitic and not attached to a substrate) organisms that dwell on the bottom of the ocean or freshwater habitats or moist places on land.

All of the flatworms that belong to class

Trematoda

,

Monogenea

,

and

Cestoda

are

parasitic

. Some are

ectoparasites

and others are

endoparasites

.

Many have

complex lifestyles

that

involve more than one host

. The

first host

is usually an

invertebrate

and the

second host

is usually a

vertebrate.

Slide5

Digestive System of Flatworms (Platyhelminthes)

The

digestive system

of

most flatworms

is referred to as an

incomplete digestive system

, having only

one opening

that serves as

both a mouth and an anus.

Turbellarians

(such as

planaria

)have a

muscular mouth

and

pharynx

that

protrudes from the ventral surface.

The

pharynx is inserted

into

prey

or

decayed organic matter

, digestive

enzymes are secreted

, and then the

pharynx brings food into the

gastrovascular

cavity

.

Digestion in

Cestodes

(tapeworms

) occurs

by diffusion.

Slide6

Digestive System of

Turbellarians

Slide7

Excretory System in Platyhelminthes

The

excretory system

of flatworms consists of a

complex network of cells

called

flame cells

connected to canals and tubes.

Flame cells (aka

protonephridia

) are

similar to kidneys

in larger more complex animals (such as the vertebrates).

The flame cells consist of

a hollow cup filled with cilia

that beat and

pump water and nitrogen waste out the body.

When the

cilia

of the

flames cells beat

they

resemble flames

.

Slide8

Flame Cells (

Protonephridia

)

Slide9

Nervous System of Flatworms

Flatworms are the first animal we have discussed in this class that exhibits

cephalization.

Cephalization

means they

have a head (anterior) and tail (posterior) region and a brain.

Cephalization

allows animals to move

(crawl, swim, fly etc.)

in a certain direction

to search for resources.

In order to make decisions, an animal requires intelligence from a

central nervous system (brain

or ganglia)

.

Slide10

Nervous System of Flatworms

The

central nervous system

in flatworms is a

region of nerve tissue

at the

anterior end

called a

ganglion.

The

ganglion

attaches to

a pair of ventral nerve cords

that

run the full length of the body.

The

nerve cords

are sensitive to

touch, chemical detection, balance (equilibrium), water current direction

and they

can control muscular movement.

The

ganglia are also attached

to

eye spots

that are

sensitive to light

(but they can not form images).

Slide11

Nervous System of Flatworms

Slide12

Reproduction of Flatworms

Flatworms reproduce both

sexually

and

asexually.

Sexual reproduction

usually occurs by

cross fertilization (exchanging sperm)

with other

hermaphrodites

.

Most

flatworms are

monoecious

. (both male and female)

Only

a few

flatworms are

dioecious

(separate sexes).

Asexual reproduction

occurs by

fission

. The organism

separates into two halves

that

regenerate into two adults.

Slide13

Regeneration of a Planarian Flatworm

Slide14

Class

Turbellaria

Free-living

, soft, flat bodies

Bodies

are

covered in cilia

Mouth

located on

ventral surface

near the

center of the body

Mostly hermaphroditic

Some

can

reproduce asexually by fission

Examples:

Dugesia

(

planaria

),

Microstomum

,

Planocera

Slide15

Class

Turbellaria

; Genus

Dugesia

,

common name

Planaria

Slide16

Class

Trematoda

; Subclass

Digenea

Digenetic Flukes

Parasitic

lifestyle with

two hosts.

First

intermediate host

is a

mollusk

.

Second

definitive host

is a

vertebrate.

Sexual reproduction

occurs in the

definitive host.

Occasionally

a

third host

(intermediate) plays a role in the life cycle.

Parasitism can occur in almost every system of the body

including the digestive, respiratory, circulatory, excretory, and reproductive systems.

Examples:

Fasciola

,

Clonorchis

,

Schistosoma

Slide17

Class

Trematoda

, Subclass

Digenea

Slide18

Class

Trematoda

; Subclass

Digenea

Digenetic Flukes

A

typical life cycle

would include the following life cycle stages;

adult, egg,

miracidium

,

sporocyst

,

redia

,

cercaria

,

and

metacercaria

.

Egg

is

released from the host's excrement

and

must reach a source of water to be released.

In the water the

egg releases a free-swimming, ciliated larva

called the

miracidium

The

miracidium

penetrates and enters the tissues of a mollusk

, and

transforms

into a

sporocyst

.

Slide19

Class

Trematoda

; Subclass

Digenea

Digenetic Flukes

Sporocysts

then

reproduce asexually

to produce

redia

.

Redia

reproduce asexually

to produce

cercaria

.

Cercaria

emerge from the mollusk

and

penetrate a second intermediate host

or

they can develop

as a

metacercaria

on

vegetation or in

the

animal host.

Metacercaria

are eventually

ingested by a definitive host

and

develop into adult flukes.

Slide20

Trematoda

(Flukes)

Slide21

Fluke Life Cycle

Slide22

Parasitic Flukes in Humans

Some

of the

most serious parasites

in

humans are flukes

.

Clonorchis

is a

liver fluke

that is common in

China

,

south Asia

, and

Japan

and can cause

cirrhosis of the liver and death.

Schistosoma

is a

blood fluke

that causes a serious infection called

schistosomiasis

. Schistosomiasis is

one of the most deadliest diseases in the world

.

There is estimated to be about

200 million people infected

with

schistosomiasis

in

Africa, South America, and the Middle East.

Symptoms

of schistosomiasis include

dysentery, anemia, enlarged

liver, bladder inflammation

and brain damage.

Slide23

Person infected with Schistosomiasis

Slide24

Parasitic Flukes in Humans

One type

of

fluke that infects birds

causes a

painful irritation

in

humans

called

swimmer's itch

.

In the case of this fluke occurring

in humans, the life cycle becomes terminated

since the

host in unsuitable

.

Children with Schistosomiasis

Swimmer's itch

Slide25

Class

Monogenea

; Monogenetic Flukes

Ectoparasites

that

attach to the gills of fish.

Hook-like mouth

called an

opisthaptor

.

Occasionally

they are

found in the urinary bladders of frogs and turtles

, but

mostly on the skin or gills of fish

.

A certain kind even lives in the eye of a hippopotamus.

Common but

cause little damage to their host

.

They

can become a serious threat when fish become crowded

, like in the case of

fish farming.

Life cycle simple

with only a

single host

Examples:

Dactylogyrus

,

Polystoma

,

Gyrodactylus

Slide26

Monogenea

Image on the right found on the gills of a fish

Slide27

Class

Cestoda

(Tapeworms)

Long flat bodies

with a

hook-like mouth

called a

scolex

. The

scolex

is used for attaching to the intestinal wall of it’s host.

The

rest of the body

is followed by

regular repeating units

of

reproducing sections

called

proglottids

.

The

main body

of a

tapeworm

is a

chain of

proglottids

called a

strobila

.

No digestive tract.

Nutrients

are

absorbed across the skin

by

diffusion.

Slide28

Tapeworm Anatomy

Slide29

Class

Cestoda

(Tapeworms)

All tapeworms

require at least two hosts.

Adults are parasitic

in the

digestive tract of vertebrates.

Almost

ALL

vertebrate species

can

become infected

, but

adult

tapeworms

do very little harm to their hosts.

Humans

often

get infected

by

consuming raw

or

rare beef, pork, or fish (larva form cysts in the muscle tissue).

Children

often

become infected

by

putting their fingers in their mouth

after

touching infected animals.

Slide30

Class

Cestoda (Tapeworms)When the larva

are

ingested

by

an

intermediate

host

(cattle, pigs, dogs etc.) then the larva can

migrate to the skeletal muscle

where they become

larval cysts

called bladder worms (cysticerci)

Occasionally larval cysts (called bladder worms)

can develop in the brain

leading to

severe brain damage

and

death

(

cerebral

cysticercosis

).

Slide31

Pork Tapeworm Life Cycle

Slide32

Beef Tapeworm Life Cycle

Slide33

Tapeworm

Slide34

Tapeworm

Scolex

Slide35

Proglottids

Slide36

Phylum

Nemertea

(Ribbon Worms) and Phylum

Gnathostomulida

(Jaw Worms)

Ribbon Worms

and

Jaw Worms

are

similar to animals in the Phylum Platyhelminthes

in several ways,

but have some important differences

,

placing them in their

own phyla

.

Both

are

acoelomate

and

bilaterally symmetrical

.

Ribbon worms

have

flame cells

and

ganglia.

Some ribbon worms

can

regenerate

like planarians.

However,

unlike flatworms

,

ribbon worms

have a

complete digestive tract

with

both

a

mouth and an anus.

Ribbon worms

also have a

circulatory system.

Jaw worms

are a

newly discovered species

and have

yet to be properly classified.

They do

somewhat resemble rotifers

.

Slide37

Ribbon Worms and Jaw Worms

Ribbon Worms

Jaw Worms