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Honors Biology
Module 11 Invertebrates - Part 2
February 4, 2016
Class Challenge
The Longest L-O-N-G Jump
Act out your favorite scene from a movie.
Quiz
Body Symmetry: Spherical, Radial, Bilateral
ID the following:
A.
B.
C.
Draw and label the life cycle of a
Jellyfish
1.
2.
3.
4.
5.
6.
Symmetry
A. Bilateral
B. Spherical
C. Radial
(total 3 points)
Draw and label the life cycle of a
Jellyfish
1. Adult jellyfish that produce a sperm and egg.
2. Results in a fertilized egg
3. Planula
4. Polyp forming
5. Polyp forming medusas
6. New released medusa
(each question should have proper drawing and label
– possible 2 points each)
Earthworm Dissection
Supplies:
• Dissection tools and tray
• Earthworm specimen
• Magnifying glass
• Lab notebook
OBJECT: To become more familiar with the
earthworm’s anatomy through dissection
Step 1
Assemble your tools. You will need a Styrofoam
tray, like the kind the butcher puts your steaks in,
a selection of Exacto knives and blades, a
shallow bowl filled with isopropyl alcohol and
some pins with brightly colored balls on their
tops as used in sewing.
• Manicure scissors work well for those who
cannot easily work with small things and fine
detail. A magnifying glass with a light source is
not a bad idea either. Unless you have
especially gifted fine motor
movement, use a toothpick to
move things around, not your
Exacto knife. Consider your
toothpick like a surgical probe,
and be gentle with it.
Procedure
1. Examine your earthworm. Rub your
fingers lightly across the surface until you
feel bristles. Those bristles are the
Setae.
Write in your lab book how
many setae you find on
each of the worm segments.
Procedure
2. Using the Magnifying glass, try to find the
nephridiopores, which are the tiny holes
near the bottom
of many segments
anterior to and
posterior to the clitellum.
3. Examine the Clitellum
In your lab book
Write down how
Many segments
there are in the
Clitellum.
Earthworm
If it is segmented and you see one or more bands, it is about to
reproduce, so you may learn more. Worms can reproduce by
themselves so do not feel guilty about dissecting a pregnant
worm.
• After you have observed the
anesthetization of the earthworm,
quickly remove it from the isopropyl
alcohol.
Now you are ready to begin the
dissection.
4. Place the specimen ventral side (the side
with the setae) DOWN on the tray. Pin the
anterior and posterior end to the pad, as
shown in your book.
Gently take the tip of your thinnest
exacto knife blade and insert it into
either end that shows an opening. If you
have manicure scissors, you can cut
instead, but in any case, do not go more
than a quarter inch and keep the knife tip
or scissors up, try not to go deep at all.
Quickly put a pin near your first incision
so it is secure to the Styrofoam tray.
Continue gently cutting a line as straight
as possible down the length of the
worm.
The worm has mud in it, It is not pus.
5. Use your scissors to cut…
Carefully through the body wall. Start about
an inch posterior to the clitellum and just to
the left of center. Being careful not to cut
anything but the body wall, extend your cut
all the way to the anterior end as shown in
your book.
Stop occasionally and gently pin the worm to
the Styrofoam board by alternating your
pins. If you find that you have rolling, gently take
a toothpick and run it along your incision on one
side only, because the tiny segments you see on
the outside continue to the inside as ribs ( they
are really muscles) so the worm tends to be
ROUND . The toothpick breaks up the
roundness so you can make it FLAT.
Pull apart the edges
Of the cut and take a look.
• You will see the intestines.
• The space between the body wall and
the intestine is called the body cavity.
• The body cavity is separated by
partitions that run from the body wall to
the intestine. These are the septa.
Using your forceps (tweezers)
And your probe (the tool with the metal pointer), break
the septa so that you can peel back the body wall.
Peel back the body wall on both sides of the cut and
pit it down, as shown in the picture.
Now the internal structures should
be visible.
Make a drawing of your dissected
earthworm in your lab book. As you
identify the structures, label them in your
drawing.
Note any structures you could not see, as
well as any organs that you saw but could
not identify.
Using Figure 11.7 identify the
following digestive structures:
1.
2.
3.
4.
5.
6.
7.
Pharynx – thick walled structure in the area of segments
4-7.
Esophagus- The structure that extends from the pharynx
to about segment 14.
Crop- a bulge just posterior of the esophagus.
Gizzard- the structure posterior to the crop.
Intestine- The structure that extends from the gizzard to
the anus.
Seminal vesicles – the larger structures on either side of
the esophagus.
Seminal receptacles – the smaller structures on either
side of the esophagus.
Review the functions of these
structures as described in the text.
Using Figure 11.7 identify the following
circulatory system structures:
1.
2.
3.
Dorsal blood vessel – A dark vessel running along the
dorsal side of the intestine. It might actually lie on the
intestine.
Aortic Arches – You will have to remove the seminal
vesicles and septa to see the arches clearly. Remove them
only from the left side of the earthworm and examine the
aortic arches that are revealed. They will look like tubes
surrounding the esophagus.
Ventral blood vessel- Use your probe to move aside (do
not remove) the intestine near the posterior end of your cut.
This should reveal the ventral blood vessel, which looks very
similar to the dorsal blood vessel.
Locate the Nephridia
The best way to do this is to extend your cut
another two inches to the posterior. Without
tearing the septa, use your probe to lift up the
intestine from this region and use your
magnifying glass to look under the intestine and
find the nephridia. They will be in all segments
except the first three and the last one, so there
should be plenty to see. If you cannot find them,
don’t worry. They are the most difficult of the
earthworm’s internal structures to find.
Using Figure 11.7
1. Find the ganglia that form the
earthworm’s brain. They should be just
anterior to the pharynx.
2. Follow the ventral nerve cord from the
ganglia. Note the small ganglion (which
looks like a bulge) that appears at each
segment.
Reproductive system
1. Carefully remove a portion of the
digestive track. Do so by cutting across
the intestine near the clitellum. Make a
similar cut just posterior to the pharynx.
2. You have now cut out a section of the
digestive tract. Gently pull that section
(that portion of the intestine, gizzard,
crop, and esophagus), out of the
earthworm.
1. Look for the ventral nerve cord. It might
have been damaged when you remove
the portion of the digestive tract. Can
you see the ganglia on the nerve cord
better now?
2. You should notice that the seminal
vesicles and seminal receptacles are
also below this portion of the digestive
tract, not just to either side of it.
Dispose of your specimen
Clean and dry your dissection tools, tray,
and pins. Put everything back in it proper
place.
Homework
Finish reading Module 11
Complete the OYO questions for Module 11
Complete the Study Guide questions
Module 11
Complete the dissection lab in lab book.
Class Challenge: Act out your favorite scene
from a movie.
Quiz: Earthworm dissection