Download The Phylum Annelida

The Phylum Annelida
© Amy Brown – Science Stuff
This phylum consists of
segmented worms.
These segmented worms may
live in fresh water, salt water, or
on land.
Class Oligochaeta
(Earthworms)
Class Polychaeta
(Marine Worms)
Class Hirudinea
(Leeches)
Phylum Annelida
This phylum is divided into
three classes:
The term “annelid”
means “little rings”.
 This
name refers
to the many body
segments that
compose the body
of a segmented
worm.
There are about 15,000 species of
worms in this phylum. They all have:
Bilateral
Symmetry
Segmentation
A True
Coelom
Three Germ Layers:
Endoderm, Ectoderm
and Mesoderm
Advantages of a True
Coelom
The true coelom and
The coelom is
three germ layers
partitioned or divided
allows annelids to
into compartments.
have the most complex Different parts of the
body structure of all
body can contract or
the worms. All organ expand independently
systems are present.
of one another.
Setae and Parapodia
Setae: external bristles
on the body; used for
movement
Parapodia: fleshy
appendages on each side
of most body segments
The number of setae and the presence or absence of
parapodia is the basis for dividing the annelids into the
three classes.
Class Oligochaeta
Generally live in the soil or fresh water.
These worms have no parapodia.
The word “oligochaeta” means “few bristles”.
These worms have very few setae.
This class includes the earthworms.
External Structures of the
Earthworm
1) Prostomium / Mouth
2) Setae
3) Clitellum
4) Cuticle
5) Anus
It is the first body
segment in an
earthworm.
Prostomium
It is in front of (but
does not include) the
mouth.
It is a lip-like
extension over the
dorsal surface of the
mouth.
Contains both male and female
reproductive structures.
Setae
In
earthworms, there are
4 pairs of setae per
segment.
They
are used for
movement. They anchor
the worm in the ground as
the longitudinal and
circular muscles contract
and expand.
Cuticle
The cuticle is a waxy,
outer covering.
It prevents water loss
and enables gases to
diffuse through the
skin.
Movement of the
Earthworm

Circular and longitudinal
muscles line the interior
body wall of the
earthworm.

The setae are used to
anchor the worm in the
ground.

Circular muscles
contract making the
earthworm longer.

Longitudinal muscles
contract making the
earthworm shorter.
Internal Structures of
the Earthworm
1) Prostomium
2) Pharynx
3) Aortic Arches
4) Esophagus
5) Crop
6) Gizzard
7) Seminal Receptacles
8) Seminal Vesicles
9) Sperm duct
10) Intestine
11) Clitellum
12) Setae
Feeding and Digestion
1. Earthworms ingest soil as they burrow through it.
2. Soil is sucked into the mouth by a muscular
pharynx and then passes down the esophagus.
3. The soil and food enters the crop – a temporary
storage area.
4. From the crop soil moves into the gizzard. The gizzard is thick and
muscular. The gizzard grinds the soil, releasing and breaking up
organic matter.
5. As the soil passes through the intestine, digested organic compounds
and nutrients from the soil are absorbed into the bloodstream.
6. Undigested material is eliminated from the body through the anus.
Did you know that the earthworm’s
digestive system is very helpful to us?
a. Earthworms fertilize the soil by
taking in decaying organic matter
and eliminating the wastes.
b. The burrows made by earthworms
allow air to penetrate into the soil,
bringing oxygen to plant roots and
other living organisms.
c. Earthworms loosen the soil, making
it easier for plant roots to grow, and
for water to seep in.
The earthworm has a closed circulatory system.
Closed
Circulatory
System
• The blood is contained
within a system of blood
vessels.
• Found in all vertebrates as
well as the annelids
Open
Circulatory
System
• The blood is not entirely
contained within blood
vessels.
• Found in Arthropods and
some Mollusks.
What is the purpose of the
circulatory system?
The purpose of the circulatory
system is to transport oxygen,
carbon dioxide, nutrients and wastes
through the body of the worm.
The earthworm’s circulatory
system consists of:
Ventral
Blood Vessel
– takes blood
to the
posterior end
of the body.
Dorsal
Blood Vessel
– returns
blood to the
anterior end
of the body.
Aortic
Arches –
contract to
send blood
through the
circulatory
system.
Respiration and Excretion
How are oxygen and carbon
dioxide exchanged? Why
must the skin stay moist?
How does the skin stay
moist? What are nephridia?
O2 and CO2 diffuse directly through
the skin. Just under the skin is a
series of very small blood vessels.
The gases diffuse through the skin
and into and out of these blood
vessels.
The skin must remain moist for the diffusion
of gases to occur. Gases cannot diffuse
across a dry surface.
The skin is covered by a thin cuticle as well as
mucus to keep it moist.
Nephridia are excretory tubules found just
under the skin. They eliminate cellular wastes
and excess water.
Nervous
The nervous system consists of several ganglia
System
and a ventral nerve cord.
Ganglia: A mass of nervous tissue that
serves as a very primitive brain.
The ganglia (anterior brain) can respond to simple stimuli
such as light, touch, chemicals, moisture, temperature and
vibrations.
There are no
specialized sense
organs.
Reproduction
Hermaphroditic:
A single worm
has both male
and female
reproductive
organs.
Sperm is produced in the testes and
stored in the seminal vesicles.
Mating occurs when two worms fuse their bodies
together at the clitellum.
They exchange sperm; the exchanged sperm moves
into the seminal receptacle where it is stored.
The exchange of sperm occurs through the sperm
duct.
After several days, the clitellum secretes a tube made
of mucus and a carbohydrate called chitin.
Fertilization occurs in this tube.
The eggs hatch in 2 – 3 weeks.
Class Polychaeta
The term “polychaete” means
“many bristles. This refers to
the many setae that help
polychaetes move.
Polychaetes
differ from
other worms
in that they
have antennae
and
specialized
mouthparts.
Class Hirudinea
This is the smallest class of
annelids. It consists of only
300 different species of
leeches.
Leeches
have no
setae.
Leeches are parasites. They have a sucker
that is used to attach to the host body and
suck blood. They secrete two substances:
an anesthetic to prevent the host from
feeling it, and another substance to prevent
the blood from clotting.
Leeches are often used for medicinal purposes.
Leeches are used to suck out blot clots
from a wound, to promote circulation,
and to relieve pressure in a joint or
wound.
What are the advantages to a segmented body?
Body segmentation makes it possible for
different parts of the body to contract or
expand independently of the other
segments.
Some organ systems can be duplicated
in several different segments which
provides insurance against injury.
How do polychaetes differ from earthworms?
Polychaetes have more setae than
earthworms. Most polychaetes live in
marine environments. Most
earthworms live in the soil.
Polychaetes may have antennae and
advanced mouthparts.
How are some leeches adapted to a
parasitic way of life?
Leeches have suckers to attach to the
host to suck blood. Leeches secrete an
anesthetic to prevent the host from
feeling their presence. They secrete a
second substance to prevent the blood
from clotting.
How are the parasitic leeches different from
the other parasitic worms such as the
tapeworms and liver flukes?
1.Leeches are external parasites
where the tapeworm and fluke are
internal parasites.
2.The flukes must cycle between two
hosts, a primary host and a
secondary host. Leeches do not.
Why do the earthworms require a moist
environment?
The earthworm exchanges gases
(carbon dioxide and oxygen) by
diffusion across the skin surface. This
exchange can take place only if the
skin is moist.