Flatworms and Roundworms

Classification of Worms

Kingdom: Animalia

Phylum: Platyhelminthes (flatworms)

Phylum: Nematoda (roundworms)

Planaria

Flukes

Tapeworms

There are over 18,000 species of flatworms.

They are divided into three classes:

Flatworms can be:

Free Living: They live on

their own and are not

parasites.

Endoparasites:

They live inside a host.

Ectoparasites:They live on the outside of their

host.

The flatworms are the simplest (least complex) animals to have:

Bilateral Symmetry

Flatworms develop from three germ or tissue layers:

Endoderm Mesoderm Ectoderm

• Will only advance as far as simple tissues

• Examples: Sponges and Cnidarians

Two germ layers

• Will develop organs, bones and muscles

• Flatworms and more advanced animals

Three germ layers

Flatworms are ACOELOMATES

The three germ layers are packed very closely together to form a solid body.

There is no coelom (hollow, body cavity) between the endoderm and mesoderm.

They will not have:

Respiratory system

Circulatory System

How can flatwormssurvive without these two very important systems?

All cells are in close proximity to the external environment. O2 and CO2 are exchanged directly with the environment by diffusion.

The digestive system has onlyone opening. Food entersand wastes leave through thesame opening.

Cephalization:

The brain and sense organs are centered in the anterior part of the body.

1 = eyespot

2 = pharynx

A = Anterior

B = Dorsal

C = Posterior

D = Ventral

1 = Brain or ganglia 2 = Eyespot3 = Pharynx 4 = Ventral Nerve5 = Intestine 6 = Mouth

Planaria feed on bits of decaying plant or animal matter. They may also feed on protozoa.

• The pharynx is extended outside of the body and is used to suck food into the intestine.

Digestion occurs in the intestine and nutrients move to other cells by diffusion.

• Food must enter and wastes must leave through the same opening.

Digestion in Planaria

Excretion in Planaria

Planaria must constantly rid themselves of excess water.A series of excretory tubes runs the length of the body.Each tube is connected to several flame cells. Flame cells enclose a tuft of beating cilia. The flame cell collects excess water and excretes it through pores in the body surface.

Nervous System of the Planaria

There are two ganglia at the anteriorend which serve as a primitive brain.

Eyespots are sensitive to light.

Can respond to simple stimuli such as: heat,

cold, touch, light, chemicals.

Has a ladder like arrangement of nerves from the

brain to the body.

Reproduction in Planaria

Asexual Reproduction

Binary Fission:

The organism splits in

two, then grows back the

missing parts to form two

complete planaria

Regeneration:

The ability to grow back

lost or missing body

parts.

Reproduction in Planaria

Sexual Reproduction

Planaria are hermaphroditic:

They have both male and female reproductive

structures.

They simultaneously fertilize each other

Eggs are laid in protective

capsules that stick to rocks.

They hatch in 2 to 3 weeks.

Parasite

Lives on or in the body of another organism

Host

The “other” animal;The organism upon

which a parasite lives

DegenerationWhich system in a parasitic worm is most often lost or

reduced? Why?

Certain body systems are lost or

reduced in size.

The digestive system is often lost. The parasite absorbs food that has already been digested

by the host.

Another characteristic of parasitic worms…..

The size of the parasite is limited by the size of the host.

Intestinal parasites have hooks and suckers to cling to the wall of the intestine or other body surface.

Parasitic worms often have a thick cuticle.

This prevents the worm from being

digested while in the intestine of the host.

The reproductive

system is often the most

advanced body system.

Proglottids contain the reproductive structures. They break off and are eliminated with the feces.

Characteristics of Parasitic Worms – A Review

Must have a host.

Degeneration

The size of the parasite is limited by the size of the host.

Hooks and suckers.

A thick cuticle.

Advance reproductive system.

Flukes

There are about 9,000 species of flukes.

May be endoparasites

May be ectoparasites

Flukes have two hosts.The Primary host is a

mammal such as a sheep or human. A primary host is an

animal from which an adult parasite derives its

nourishment.

The intermediate host is a certain species of

snail. An intermediate host is an animal from which a larval parasite

derives its nourishment.

Life Cycle of the Flukea) Fertilized eggs leave the

human through the feces.

b) If the eggs land in water, they hatch into larva.

c) The larva enters the body of a snail where it reproduces asexually.

d) The larva develops a tail and escapes the snail.

e) The tailed larva swims in the water. If they encounter the bare skin of a human, they will penetrate the skin and enter the body.

Tapeworms may live in the intestines of almost all

vertebrates.

Tapeworms may enter the host when the host eats raw or

undercooked meat containing the eggs or larva of the tapeworm.

Symptoms include:

Digestive problems, weight loss, lack of energy and anemia.

Tapeworms

The body of the tapeworm consists of a scolex and many proglottids.

Scolex:• Found on the anterior end• Contains hooks and suckers to attach to the host

Proglottids•Body sections containing complex reproductive structures•New proglottids are added on the anterior end behind the scolex.•Mature proglottids break off from the posterior end and leave the host through the wastes.

A single tapeworm may have 2,000 proglottids and exceed 33 feet in

length!