Download Biology 213, Lab 4

Biology 212; Winter 2008
Focus: Phylum Annelida/Phylum Mollusca
Laboratory objectives
I.
To become familiar with the key characteristics of Phylum Annelida and Phylum Mollusca.
II.
To compare two of the classes within Phylum Annelida (Class Polychaeta and Class
Oligochaeta)
III.
To view the key Molluscan characteristics for four Classes of Phylum Mollusca: Bivalvia (i.e.
mussels), Gastropoda (snails and slugs), Polyplacophora (chitons) and Cephalopoda (i.e. squid,
octopus.),
IV. To understand how the differences of the major Molluscan characteristics among Classes is
related to their differences in lifestyle.
V.
NOTE: You will record your observations on the charts provided. This chart is designed
to help you compare the appearance and function(s)/special adaptations among the classes
of Annelida or Mollusca. In the case of Phylum Mollusca, you will note the similarities
and differences for each feature compared to the “hypothetical ancestral mollusc”
described in the introduction.
A.
Although I am providing you with diagrams to help identify parts, your sketches and
descriptions should be based on what you see, not just re-sketches of the drawings. I can
tell the difference, and you will see some actual specimens in the lab exam!
Phylum Annelida, Classes Polychaeta (the marine worm, Nereis sp.) and Oligochaeta (the
earthworm Lumbricus sp.):
I.
Sketch and label the cross-section of Phylum Annelida, Class Oligochaeta labeling the
following:
A.
epidermis derived from ectoderm
B.
circular muscles derived from mesoderm
C.
longitudinal muscles derived from mesoderm
D.
coelom (true coelom/eucoelom)
E.
muscle layer on intestine side of coelom (probably both circular and longitudinal, but
difficult to tell in the cross sections) derived from mesoderm
F.
gastrodermis derived from endoderm
G.
blood vessel (part of its closed circulatory system)
II.
Compare the following aspects of these two classes in the worksheet provided. The two
annelids will be similar for some features and different for others. We will examine the Nereis
as a group, and then you will examine your earthworm in groups of two. Characteristics to
examine include:
A.
Overall shape
B.
Body segmentation: Are segments obvious?
C.
Head regions: Compare the presence/absence of sensory structures including tentacles
and eyes.
D.
Hairs (a.k.a. “chaetae” or “setae”). Many or few? Location?
E.
Leg-like parapodia. If present, describe.
1.
Note that sometimes parapodia are key surfaces for gas exchange. Are the
parapodia you see likely to have that function? Explain your answer.
F.
Movement. Describe as precisely as possible and point out differences.
III. If there is time at the end of the lab (after completing Phylum Mollusca) you may dissect your
earthworm. Use your lab manual and Photographic Atlases. May also be possible next week.
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Phylum Mollusca
I.
Introduction: The key characteristics of Phylum Mollusca (mini-lecture)
II.
Class Bivalvia (example: the mussel): You will conduct a systematic dissection of the
California mussel, Mytilus californianus. You will sketch/describe the key Molluscan features
as they appear in the mussel, and view their method of feeding. Complete the chart provided
(with both sketches and descriptions) as you explore each key feature. Be sure to keep the
mussel submerged in seawater except during the shell removal process!
A.
Shell
1.
Sketch and describe the shell, comparing its general appearance and its apparent
function(s) to that of the hypothetical ancestral mollusc (HAM.) HINT: Be sure to
state the obvious, such as the number of “valves” or pieces that comprise the shell,
whether it is thick and protective, and the extent to which it covers the body parts.
Take time to examine anything growing on its shell.
B.
Mantle and associated structures:
1.
Break one of the valves and carefully pick off the pieces of the shell as shown in
the demonstration. (Do not simply open up the mussel as you might if you were
eating it!) Underlying the shell is the mantle. The gonads are imbedded in the
mantle tissue.
2.
Sketch/describe the mantle tissue. Be sure to include a sketch/description of the
sensory tentacles at the mantle edge that can extend out of the shell. Be sure to
note functions of the mantle itself as well as of the tentacles.
C.
Mantle cavity/ctenidia:
1.
Carefully lift the mantle tissue up and cut this tissue carefully as needed to reveal
the ctenidium below it. Do not remove the ctenidium! The large cavity that
houses the ctenidia is the mantle cavity.
2.
Use the dissecting microscope to view the weave of the ctenidium. Spend time
playing with the fiber optic lights, zoom and focus to so that you can see its fine
mesh with a “groove” at the bottom where two layers meet. (Ask me for help if
you don’t see it.) Make a sketch of the overall ctenidium as it sits in the shell,
noting “anterior”, “posterior”, “dorsal” and “ventral” positions as well as its weave
and groove.
3.
Add carmine solution to the ctenidium with the pipette. You should put the tip of
the pipette almost touching the ctenidium. Quickly look through the microscope
and note the direction(s) of particle movement.
a)
Add arrows that show movement of the carmine to your diagram. Be sure
to note what is happening along the surface of the ctenidium as well as
within the groove.
4.
After everyone in your group has finished step #3, remove the top ctenidium and
place it on a microscope slide. Add water and a coverslip and examine it through
the compound microscope. You should be able to see the individual ctenidial rods
as well as the “groove” where the two thin layers of the ctenidium meet. Start with
low power, and then zoom in on the detail. You should clearly see cilia. mucus
a)
Sketch a close-up view of the ctenidium that shows the ctenidial rods and
the cilia.
b)
Is there evidence of mucus? If so, describe/explain.
5.
Compare the mantle cavity and ctenidia in the mussel to that of HAM.
D.
Head and associated sensory structures
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1.
E.
Do you see anything resembling a head? What about a mouth? You should see
two flaps, called “Palps”, at the anterior end of the mussel. Sketch/describe them.
(Don’t need the detail to the level that you drew the ctenidium.
Foot and associated structures
1.
You will see the foot extending out ventrally. Sometimes it is withdrawn into the
shell during the dissection. Sketch and describe it, comparing it to the foot of
HAM.
III.
Class Gastropoda (example: the limpet) You will examine a living limpet collected along the
Oregon coast through the dissecting microscopes. You will not dissect it! It must be kept
submerged at all times! You will be able to see most of its features by turning it ventral-side up.
Sometimes it will stick to a slide to make viewing easier.
**I have provided some hints for viewing below, but for all parts, your goal is to
sketch/describe the key Molluscan features as they appear in the limpet, comparing it to
the “hypothetical ancestral mollusc”, HAM (and to other molluscs as you wish) in the
chart provided.
A.
Shell
B.
Mantle and associated structures:
1.
You will see the mantle tissue “lining” the shell when viewing the shell from
beneath. Sketch and describe it. HINT: Zoom in on the mantle edge for a closeup view of sensory tentacles.
C.
Mantle cavity/ctenidia:
1.
The mantle cavity is located above/around the head of these limpets. It appears as
an obvious space. You will hopefully be able to view the feather-like ctenidia
within it if you look carefully to one side of the head.
D.
Head and associated sensory structures
1.
Do you see anything resembling a head? What about a mouth? Any tentacles?
Any eyes? (Note: Many gastropods have eyes.) Do you see its radula?
E.
Foot and associated structures
1.
Compare to the mussel’s foot as well as to HAM’s foot… Also note whether there
are sensory tentacles associated with the foot.
F.
NOTE: Be sure to view the nudibranch, also in Class Gastropoda.
IV.
Class Cephalopoda (example: squid): You will conduct a dissection of a squid and describe
the key Molluscan features as they appear in the squid. Complete the chart provided as you
explore each key feature. You will also learn parts of the squid as listed in “additional features”.
Any squid parts named are fair game for a lab exam! In addition to this handout, a detailed
dissection guide has been provided.
A.
Examine the external features of the squid. Those with asterisks (*) require an entry on
the chart of the key Molluscan feature and comparisons with HAM!
1.
Mantle and associated structures (fins, for example)*.
2.
Head*: Note that the arms are not actually part of the head, but the two long
tentacles are probably derived from the original cephalic tentacles of HAM.
3.
Mantle cavity* (you will see the ctenidia after you dissect the squid)
4.
Foot*: In cephalopods, the foot has evolved into the funnel (a.k.a. ‘siphon”) and
the arms (8); the two long tentacles are derived from the______, not the foot.
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B.
C.
D.
E.
F.
V.
Cut the squid’s mantle open longitudinally, on the side opposite the pen. This will
expose the mantle cavity. You will now be able to identify additional structures (see
diagram):
1.
Funnel (or “siphon” retractor muscles)
2.
Cephalic retractor muscles
3.
Ink sac
4.
Ctenidia (a.k.a. “gills”)*
5.
Branchial (or ctenidial) hearts
6.
Systemic heart* (Think about circulatory system in cephalopods vs. others.)
7.
Ovaries (female)
8.
Nidamental glands: Find in the female; these put on the outer egg casing once the
eggs are fertilized.
9.
Testes (or “spermatophore sac”): males
10. Penis (male): You should be able to see spermatophore within the penis.
11. Visceral mass
12. Stellate ganglia (location of the “giant synapse”) and the giant axons.
Dissect the eye and find the lens. What shape is the lens?
Dissect the head and find the beak. You might find the radula, but that is unlikely.
Remove the pen*. This is all that remains of the shell. How is the reduction of the shell
adaptive in the cephalopods?
1.
Write your name in pen and ink on one of the handout pages.
Quiz your partner on all parts, including the evolutionary origins of key structures.
Class Polyplacophora (chitons) View the diagram (sorry, no live ones this year) and include
descriptions on the chart. (If time is short, you can do this as homework.)
A.
Shell.
1.
HINT: Be sure to note the number of shell plates and speculate about the
advantages of multiple shell plates.
B.
Mantle and associated structures:
1.
HINT: Again, think about how it differs structurally from HAM, and how this
could be an advantage to it (think about in conjunction with the multi-plated shell.)
C.
Mantle cavity/ctenidia:
1.
Where is the mantle cavity? How does this compare to HAM? What is different
about the ctenidia compared to HAM?
D.
Head and associated sensory structures
1.
Do you see anything resembling a head? What about a mouth? Any tentacles?
Any eyes?
E.
Foot and associated structures
1.
Compare to the other molluscs you have already seen… Also note whether there
are sensory tentacles associated with the foot.
TO TURN IN (at the beginning of next week’s lab:
1.
Worksheet comparing members of four classes of Phylum Mollusca
2.
Essay: For each feature in the Mollusc worksheet, describe the similarities and differences you
see among the 4 classes based on how the animals are adapted to their particular environment
and lifestyle. This should be formatted similar to the paragraphs you wrote for each feature in
lab 1 (one paragraph per feature), so be sure to look at the sample paragraph for that lab.
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Phylum Annelida, Classes Polychaeta (the marine worm, Nereis sp.) and Oligochaeta (the earthworm
Lumbricus sp.): Complete the chart as you compare these two different classes of worms. You may use
sketches, descriptions or both within the chart. The idea is to point out the major differences and features. Use
additional paper if needed!
Feature
Overall shape
Class Polychaeta
Class Oligochaeta
Body segmentation (Are
segments obvious? How
do relative sizes
compare?)
Head region: compare
presence/absence of
sensory structures
(tentacles, eyes, etc…)
Hairs (setae): many or
few? Location?
Describe…
Parapodia: If present,
describe. Also indicate
whether they are likely to
function in gas exchange.
Movement: Describe
precisely and point out
differences.
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Phylum Mollusca: Complete the chart with sketches and descriptions (see written portion of lab for more details.)
Feature
Class Bivalvia: mussel
Class Gastropoda: limpet
Class Polyplacophora:
chiton
Class Cephalopoda: squid
Shell
Mantle and
associated structures
Mantle
cavity/ctenidia
Head and associated
sensory structures
(eyes, tentacles,
etc…). Also
comment on the
mouth here.
Foot and associated
structures
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