MOLLUSKS
SECTION 1
I.
Instructional Objectives
A. The student will
be able to list two lines of evidence that the annelids and the mollusks are
related.
B. The student will
be able to summarize the advantages of a true coelom.
C. The student will
be able to list four characteristics of the mollusks.
D. The student will
be able to contrast respiration in the terrestrial snails and marine snails.
E. The student will
be able to list the four major classes of the phylum mollusca.
II.
Set
Take out a sheet of paper and glance
through the chapter for just a minute and list three animals that are
classified as mollusks. (Get student
answers.) Can anyone name one mollusk
that is found in the water that we are familiar with. Many of the mollusks are considered excellent foods. And the mussel shell, in many areas, once
provided us with many items such as buttons and pearls. The mollusca phylum contains 100,000 species,
second only in size to the phylum arthropoda.
Since there are so many of these organisms in our ecosystem we should
strive to learn more about them. You
have already studied the flatworms, in this chapter we will discuss the
mollusks and the annelids.
III. Instruction
A. Input
1.
Although they look very different, snails, clams, mussels, and octopuses
are all mollusks. The term mollusk
comes from a Latin word meaning "soft" and refers to the bodies of
these animals. Although some of these
do have soft bodies, most of the mollusks have an outer shell that hides their
soft body.
2.
Mollusks and annelids are very different in appearance. Despite this difference they are linked by
two of their characteristics.
a.
Both annelids and mollusks have a true coelom. The coelom is a fluid filled cavity within the mesoderm. There are several benefits of the
coelom. First, the coelom separates the
muscles of the gut from those of the body wall. This allows food to move through the digestive tract independent
of locomotion. Second, the coelom
provides a space in which the circulatory system can function without
interference from other organs. Third,
the coelom provides a hydrostatic skeleton against which the muscles can
contract.
3.
Another link between the annelids and the mollusks is the trochophore
larvae. Both, develop from a larvae
known as a trochophore. The trochophore
is a free swimming larvae with cilia at
each end. In the terrestrial mollusks and
marine annelids the trochophore develops in an egg and is not free living.
4.
The mollusks are a diverse group.
Some are sedentary feeders such as the clam and the oyster. Others such as the octopus and the squid,
are predatory and move about with jet propulsion. Although they are very different, the mollusks share four
distinct characteristics.
a.
All mollusks have a true coelom.
b.
The body of mollusks have three distinct parts: the muscular foot, the head, and the
visceral mass.
c.
Mollusks have organ systems for circulation, respiration, digestion,
excretion, nerve impulse conduction, and reproduction.
d.
Most mollusks display bilateral symmetry and have more than one shell.
B. Monitor and Adjust
1.
What are two lines of evidence that show that annelids and mollusks are
related?
2.
What are the advantages of the true coelom?
3.
While some mollusks are filter feeders others are ?
4.
What are four characteristics of mollusks?
C. Input
1.
Notice the diagram at the bottom of page 466. Lets find the three main body parts of the mollusks. The muscular foot is a large muscle
used for locomotion. The head is
the anterior part of the organism that contains the sensory organs, the mouth,
and the cerebral ganglia. The visceral
mass contains the heart, and organs of digestion, excretion, and
reproduction. Covering the visceral
mass is the mantle that in most species secretes the shell.
2.
Biologists use several characteristics to further classify the mollusks
into four classes. There are four major
classes that we will discuss:
polyplacophora, gastropoda, bivalvia, and cephalopoda.
3.
CLASS POLYPLACOPHORA -- Members of this class are called chitons. These animals primarily live on the seashore
on rocks. The word polyplacophora means
"many plates". This name is
used because their body is divided into eight separate overlapping plates.
4.
CLASS GASTROPODA -- The name gastropoda means "stomach
foot". Most gastropods have one
shell or valve and thus, are called univalves.
Slugs and some other gastropods have no shell.
a.
Snails -- Snails live in a wide range of environments. Some live in aquatic environments, some in
marine environments, and some are terrestrial.
Aquatic snails respire by the use of gills in the mantle cavity. In terrestrial species, the mantle cavity
acts as a modified lung that takes oxygen from the air. The thin membrane that lines the cavity must
be kept moist to allow gases to diffuse through it. The main feeding adaptation of snails is the sawlike RADULA,
a thin flexible tonguelike strip that has chitonous teeth. Most land snails are hermaphroditic but in
most aquatic species the sexes are distinct and the eggs are fertilized
internally.
D.
Monitor and Adjust
1.
Name are the three main parts of the mollusk and describe each.
2.
What are the four main classes of the phylum mollusca?
3.
What are members of the class polyplacophora called?
4.
Where are these organisms found?
5.
What does the word polyplacophora mean?
6.
How many body segments do the chitons have?
7.
What does the word gastropoda mean?
8.
What is the name given to the one shelled organisms?
9.
contrast the means of respiration in the terrestrial and aquatic snails.
10. What is the adaptation for feeding
in the snails called?
11. How do snails reproduce?
IV.
Closure
Are there any questions concerning this
material that we have discussed today?
Let's take just a few minutes and look at the notes that you have taken
today.
1.
What are two lines of evidence that show that annelids and mollusks are
related?
2.
What are the advantages of the true coelom?
3.
While some mollusks are filter feeders others are ?
4.
What are four characteristics of mollusks?
5.
Name are the three main parts of the mollusk and describe each.
6.
What are the four main classes of the phylum mollusca?
7.
What are members of the class polyplacophora called?
8.
Where are these organisms found?
9.
What does the word polyplacophora mean?
10. How many body segments do the
chitons have?
11. What does the word gastropoda mean?
12. What is the name given to the one
shelled organisms?
13. Contrast the means of respiration
in the terrestrial and aquatic snails.
14. What is the adaptation for feeding
in the snails called?
15. How do
snails reproduce?
SECTION
2
I.
Instructional Objectives
II.
Set
A. The student will
be able to describe movement in the class bivalvia.
B. The student will
be able to describe the three layers of the bivalve shell.
C. The student will
be able to explain the process of feeding and respiration in the clam.
D. The student will
be able to list and describe two other bivalves.
E. The student will
be able to explain the use of the word cephalopoda to classify the cephalopods.
F. The student will
be able to explain the processes of feeding, respiration, excretion,
circulation, sensing, and reproduction in the class oligochaeta.
G. The student will
be able to list four characteristics of the annelids.
H. The student will
be able to list one example of both the class hirudonea and the class
polychaeta.
Take out a sheet of paper and write the
name of the phylum that we are studying.
Write the four classes under the phylum mollusca. Yesterday, we studied the general
characteristics of the mollusks and the classes polyplacophora and
gastropoda. Today, we are going to
study the other two classes: bivalvia
and cephalopoda. We will also study the
annelids.
III. Instruction
A. Input
1.
In contrast to the gastropods that move aboout in search of food, most of the bivalves are sessile and filter
food from the HOH. Bivalve means
"two valves". The bivalves
move by means of a foot. This foot is
merely a muscle. The muscle extends
into the soil then blood fills the foot enlarging it and causing it to act as
an anchor. The bivalve then contracts
the muscle and pulls itself along.
Bivalves do not have a distinct head region as do the gastropods. The ganglia are attached to the foot muscle
in the anterior region.
2.
Each valve is made up of three layers secreted by the mantle. A thin outer layer protects the bivalve from
harsh HOH conditions. The thick middle
layer made of calcium carbonate crystals strengthens the shells. the smoothe inner layer of the shell
protects the body of the bivalve. If an
irritant such as a grain of sanc gets into the shell, the mantle coats the
grain with an secretion known as mother of pearl. The layers of this mother of pearl form the pearl.
a.
THE CLAMS -- Clams are bivalves that live buried in the mud or
sand. They are closed shelled, except
for the two hollow tubes called siphons.
Cilia beating on the gills cause a current to draw HOH into the shell
through the incurrent siphon. the water
passes over the gills and then exits through the excurrent siphon. As this HOH moves over the gills food,
plankton and organic sediments, becomes trapped in the mucus of the gills. The cilia movement moves the food toward a
mouth. As the HOH passes over the
gills, O2 diffuses into the blood and CO2 diffuses out
into the HOH, and is carried out of the shell with the HOH. Clams have rudimentary sense organs. Sensory cells along the mantle, are
sensative to light and touch. The clams
are diecious, meaning the sexes are distinct.
Diecious literally means "two houses". Fertilization occurs externally, and the
fertilized eggs develop into a trochophore larvae and then into an adult.
b.
Other Bivalves -- Oysters are bivalves that are permanently attached to
a hard surface. Scallops are bivalves
that move by jet propulsion, by quickly closing their shells. The teredo is not a filter feeder, but bores
into driftwood or ship timbers and tiny protozoans within the teredo digest the
cellulose in the wood.
B. Moniotor and Adjust
1.
What does the word bivalvia mean?
2.
How do the bivalves move?
3.
Explain the makeup of the valves?
4.
What produces the shell layers?
5.
How is a pearl formed?
6.
Explain the process of respiration and feeding in the clam.
7.
What do the clams feed on?
8.
Where are the sensory cells found in the clam?
9.
To what are the sensory cells receptive?
10. What does the word diecious mean?
11. Explain the reproduction in the
clam.
12. Name and describe two other
bivalves.
C. Input
1.
CLASS CEPHALOPODA -- Means "Head foot". This refers to the well developed, large
headand the prominent foot divided into tenacles. Cephalopods capture their food with the tenacles equipped with strong
succers, and eat their prey with a radula and a sharp beak. They have a closed circulatory system. Squids are the worlds largest known
invertebrates.
2.
The Phulum Annelida -- Four characteristics: true coelom; metamerism -- segmented body some segments fuse
together while others remain seperate, metameric units; Well developed organ
systems; external bristles called setae.
Three classes of annelids:
Polychaeta, oligochaeta, and hiurdinea.
The class oligochaeta contains the earthworms. FEEDING -- earthworms eat soil, it goes through the esophagus to
the crop then to gizzard where it is ground up, nutrients are absorbed as the
ground food passes through the intestine.
CIRCULATION -- closed circulatory system, 5 aortic arches. RESPIRATION and EXCRETION -- Respiration is
through the skin. Nephridia act like
kidneys and eleminate liquid wastes.
SENSORY -- Sensative to light, touch, moisture, chemicals, tempurature,
and vibrations. REPRODUCTION --
Hermaphroditic
3.
CLASS POLYCHAETA AND HIRUDINEA -- polychaeta=marine worms Hirudinea=leeches. Leeches serve some medicinal purposes. Clot busters and rejoining body parts.
D. Monitor and Adjust
1.
What does the word cephalopoda mean?
2.
Why do we use this mane to refer to these animals?
3.
What are the four characteristics of the phylum annelida?
4.
What are the three classes of annelids?
5.
How do the oligochaets feed, circulate, respire, excrete, sense, and
reproduce?
6.
What are the polychaetes?
7.
What is one example of the class hirudinea?
8.
What are two medicinal uses of leeches?
IV.
Closure
Let's take just a few minutes and look at
the notes we have taken today.
1.
What does the word bivalvia mean?
2.
How do the bivalves move?
3.
Explain the makeup of the valves?
4.
What produces the shell layers?
5.
How is a pearl formed?
6.
Explain the process of respiration and feeding in the clam.
7.
What do the clams feed on?
8.
Where are the sensory cells found in the clam?
9.
To what are the sensory cells receptive?
10. What does the word diecious mean?
11. Explain the reproduction in the
clam.
12. Name and describe two other
bivalves.
13. What does the word cephalopoda
mean?
14. Why do we use this mane to refer to
these animals?
15. What are the four characteristics
of the phylum annelida?
16. What are the three classes of
annelids?
17. How do the oligochaets feed,
circulate, respire, excrete, sense, and reproduce?
18. What are the polychaetes?
19. What is one example of the class
hirudinea?
20. What are two medicinal uses of leeches?
