Download Phylum Mollusca

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Phylum Mollusca
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*Text pages 374-375. This is required reading.
Examine the animal phylogeny below to understand the position of Molluscs in the animal
kingdom. You will observe a large diversity of molluscs at Bamfield.
What does the term Mollusca mean? __________________________
Examples:
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Are they Protostomes or Deuterostomes?
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Body Plan
The different body shapes of molluscs are variations on a single body plan as shown below.
-Study the diagram and state the functions of the three major distinguishing features of mollusks
1. Muscular Foot: _______________________________________________________________
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2. Visceral Mass: ________________________________________________________________
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3. Mantle: _____________________________________________________________________
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Do most Molluscs have a shell? Where is it created and what is its function?
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Many Molluscs have a ciliated larva. What is this called and why is it important (2 reasons)?
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*Molluscs are divided into four classes. Explore these using the specimens set up in the lab.
1. Class Polyplacophora: Chitons
http://www.oceanlink.info/biodiversity/gumboot/gumboot.html
These sluggish animals feed on algae growing on rocky
seashores. Fossilized chitons have been dated up to 400
million years old.
Lab activity: Chiton Examination
a) Place a preserved chiton in a petri dish using tweezers.
b) In the space provided below sketch the dorsal view of the
chiton, labeling the mantle and eight shell plates.
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c) In the space provided below sketch the ventral view, labeling the foot, gills and mouth if
possible. The antennae are only visible when the chiton is alive.
d) Examine the pictures of chitons found in the books on display and read the description of
chiton development found below.
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2. Class Gastropoda: Slugs, Snails, Limpets, Abalone, etc
Lab activity: Gastropod Examination
a) Place a live garden snail on a
petri dish and observe it.
b) Without harming the animal,
identify the following structures
(it may be necessary to use a
hand lens or dissecting
microscope): shell, foot, anus, mantle edge, pneumostome, mouth, eye, tentacles and genital
aperture (if visible).
c) Observe and describe below the movement of the snail’s foot (Hint: how do the muscles in the
foot move?).
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d) Compare a marine and land snail shell. The marine shell should be thicker and heavier than
the terrestrial one. How has the marine snail’s habitat permitted this difference?
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e) Use the reference books provided to name 3 common West Coast molluscs that you may see at
Bamfield.
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f) Examine the abalone shell on display. Comment on the ecological value of abalone on the west
coast of Vancouver Island. You can find information about this on the pamphlet in the lab.
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Life Cycle of Abalone
h) Using text page 374 provide at least 3 interesting (not boring) facts about gastropods.
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3. Class Bivalvia: Mussels, Clams, Scallops, Oysters
Why is this group of molluscs called bivalves?
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*Complete the sentence below using the following words: Oxygen, Cilia, Plankton, Water
Bivalves are generally stationary when feeding. They draw _______________in through a
siphon, pass it over their gills to extract ___________________and filter out
___________________ in a mucous layer. The plankton is then moved to the mouth by the
beating of ___________________on the gills.
Lab Activity: Mussel and Clam Examination
Mussels fasten themselves to rocks in the intertidal zone using though bissus threads produced by
a gland at the base of the foot. Mussels only use their foot for locomotion during the juvenile
stage of their life cycle when they are looking for a suitable habitat to live in.
a) Obtain and place a young mussel into a glass dish. Use a dissecting microscope to observe it
putting out its foot.
b) Sketch the young mussel’s external features. Identify and label its shells, hinge and bissus
threads.
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c) Use the diagram below and the display poster of clams to examine their complexity.
d) Clams and mussels live in different habitats. Name these habitats and describe adaptations
each organism has to survive there. Look at the live and preserved samples if you need help.
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*See how Bivalves are inspiring technology development! http://www.bbc.com/news/scienceenvironment-26939126
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In preparation for the upcoming Cephalopod dissection, complete the table below comparing
various characteristics of a clam (Bivalve), squid (Cephalopod) and land snail (Terrestrial
Gastropod)
Clam (Bivalve)
Squid (Cephalopod)
Land Snail (Terrestrial Gastropod)
Habitat
Feeding
Respiration
Circulatory
system
Response
Movement
Cephalisation
Nervous
System
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4. Class Cephalopoda: Squid, Octopus, etc
This name means ________________________________________________________________
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Lab activity: Squid Dissection
a) Obtain and place a fresh squid on a dissecting tray. Use the diagram below to identify as many
parts as possible.
b) Draw and label the ventral view in the space provided below. *Hint: the siphon is on the
ventral side.
c) Squid have _______ arms and _______ tentacles.
d) Position the squid with the siphon facing upwards. Make an incision from the bottom of the
mantle, above the siphon, to the tip of the mantle next to the fins. Lift up with your scissors when
cutting so you don’t damage the internal organs!
e) Spread the mantle open and use the diagram to identify the internal organs.
f) Did you dissect a male or female squid? ____________________
g) The pen is transparent and looks like it is made of plastic. You may remove it from the mantle,
dip it in ink from the ink sac and try to write with it on the line below:
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h) Remove the beak and examine it under the dissecting microscopes. Try to open the beak to
view the small, folded, plastic-like radula contained between the two beaks. Write your
observations below.
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i) Remove one of the squid’s eyes. Extract the lens. Comment on the shape and texture of the
lens. See text 595 for a description of how the lens functions.
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Discussion Questions
1. Identify the differences between squid tentacles and arms. Why are they different?
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2. How does the squid use the siphon and mantle for locomotion?
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3. How does the squid obtain oxygen from the water?
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4. Why are the chromatophores and why are they important to squid?
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5. a) What role do squid play in the ocean ecosystem?
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b) What adaptations does the squid have that allow it to play this role?
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6. Provide some additional notes on cephalopods from text page 375.
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The molluscan body plan has been modified into various classes. In the diagram below the
digestive tract is shaded, the foot is stippled and the shell is marked by a heavy black line.
Examine and compare the different Molluscs very carefully.
Questions:
1. Which group of molluscs are filter feeders, getting their food by straining plankton from the
water? _____________________
2. Which group are active predators with excellent sensory structures and very fast locomotion?
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3. Which group are mainly herbivorous and get their food by grazing on plants or scraping
algae? ________________________
4. Which group has 8 pieces of shell on the dorsal surface and clamps tightly to the rocks when
disturbed? _____________________
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