Teaching Notes for PowerPoint Presentation:
Meet the Mollusks
Refer to this expanded lesson script to assist your direct instruction for the slide presentation.
Timeline of MSC Lesson
Time
1. Introduction:
10 min.
Definition – what is a mollusk?
Characteristics of mollusks –characteristics
and background information
2. Explanation:
Slide presentation exhibiting examples of
mollusks and mollusk characteristics
3. Lab Activity:
Examination of a native gastropod,
the Mud Snail
4. Practice Activity: Review of handout and identification of
special characteristics
5. Activity:
Taxonomic Key. Classification of gastropods
and bivalves based on shell morphology
6. Practice Activity: Review of correct responses for taxonomic key
7. Closure:
Review of mollusk characteristics and
discussion of unique adaptations
20 min.
20 min.
5 min.
15 min.
5 min.
10 min.
Teaching Notes – Expanded Lesson Script
1. Introduction.
Slides # 1-5
1. Title slide
2. Introduce self and subject of lesson. What is a mollusk?
3. Slide of Octopus (blue-ringed octopus –poisonous!)
4. What is a Mollusk? Slide of Cowrie – water snail
5. Word mollusk comes from the Latin “mollusca,” which means “soft-bodied.”
A mollusk is an animal that has a soft body and may or may not have a shell.
Mollusks are soft bodied
Are INVERTEBRATES
Have 3 body parts:
Head (contains the “brain”)
Visceral mass (internal organs) with fold of skin called Mantle
Foot (muscular part of body)
* Pass out worksheets and instruct students to complete the chart side of the handout during the
slide presentation.*
2. Explanation – PowerPoint Slide Presentation
1. The Mantle
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Secretes the shell and pearly lining – a covering for protection
Skin-like organ that surrounds the mantle cavity – may have mucous glands and secrete
slime
Univalve – 1 shell
Bivalve – 2 shells
2. Mollusks and Movement
Foot – muscular organ to move, dig slide..—foot may be in tentacles or arms
Radula – rasping tongue to obtain food or drill holes in shells
(ex. Moon snail & oyster drill)
3. More Mollusk Info.
2nd largest group of animals – 100,000 known species
(largest = arthropods)
Most are marine – but can live in fresh water (zebra mussels) and land
Importance to Man? Major food source – pearls – source of calcium – cuttlebone from
cuttlefish used in bird cages – shells are pretty to collect
4. Classification
Kindgom – Animalia
7 classes of mollusks
3 major classes
Gastropods – snails, slugs, limpets
(“stomach-foot” largest class in phylum – 70% of mollusks)
Bivalves – clams, oysters, scallops, mussels
(“two-shelled” long muscular foot – dig in mud)
Cephalopods – octopus, squid, nautilus
(well developed eyes, “head-foot”)
most – no external shell – mantle = tough body wrapping
5. Land Snail
1 shell – univalve – shell secreted by mantle
muscular foot – operculum – seals opening (trap door)
breathes through skin (no lungs) – needs moist skin
many are nocturnal (few predators – moist out!)
2 pairs of tentacles – short pair used for for sensing – smell, touch
long pair has eyes on the end
6. Aquatic Snails
1 shell (univalve) – soft body, mantle, foot, tentacles
eyes on base of tentacles
siphon tube to circulate water over the gills and search for food
7. Slug
What’s missing (the SHELL)
Has mantle – produces thick layer of mucus or slime
Slime= a.helps it move b. helps it breathe c. protects (nasty taste)
Some slime irritates
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Garden Pests!!! Salt kills slugs!
8. Banana Slug
Lives in northwestern U.S. and Canada. Can be 10 in. long.
Has “lung chamber” on its side – helps in respiration
9. Nudibranch
A type of sea slug. Nudi = naked. Branch = gills.
Gills found outside of body. Bright colors warn predators.
Many eat stinging celled animals and keep stinging cells on the gills.
Large variety of sizes and colors – from ½ in. long to 19 in. long
10. More Nudibranchs
11. Bivalves
Called “Pelycypods” (“hatchet foot”)
Two shells. This is a scallop. Top pix is bay scallop in eelgrass (its natural habitat)
2 siphon tubes – (incurrent and excurrent siphons) – constant current of oxygen and food
are filter feeders and clean the water (oyster)
mantle lines shell and makes shell
scallop can swim short distances by “jet propulsion”
eyes on outside edge of shell (50 pairs of eyes here!)
12. Cephalopods
No shell – head attached directly to foot – foot divided into 8 “arms”
Arms = movement, defense, food gathering
Mouth located in center of arms – with beak
Ink sac – releases ink when threatened
Octopuses can change color for camouflage or for a warning signal
Size range for octopus is 4” to 30 ft.
Blue-ringed octopus has poisonous bite
Eyes similar to ours – perhaps most intelligent invertebrate – large brain
13. More Octopods
Swims by jet propulsion – incoming and outgoing siphon
Blue-ringed octopus small – 4 in. long – rings appear when it is disturbed
Bite can kill a person
14. Squids
10 arms (8 arms and 2 extra long-tentacles) --- elongated body
no external shell – but inside support structure called a “pen”
has ink sac, moves by jet propulsion – very fast swimmers
Size range for squids ranges from 1” to 60 ft.
Giant Squid is the largest invertebrate – possibly 60 ft. in length and 1 ton!
(found in deep Pacific near New Zealand and in North Atlantic)
have been found in stomachs of sperm whales
excellent eyesight and large brains
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A relative of the squid, the cuttlefish, has a larger internal shell. When the animal dies,
the shell is left behind and many people put it in birdcages as a source of calcium.
15. The Chambered Nautilus
Only cephalopod that has an external shell
Lives in South Pacific and Indian Oceans – called “pearly nautilus”
Has separate chambers that form as animal grows – nautilus uses these chambers to vary
pressure in its body and change buoyancy – can dive to 1500 ft. – using fluid
To rise (near surface) uses gas
Other unique mollusks include Chitons (same as its relatives 400 million years ago) – has
shell with 8 overlapping valves, clings to rocks and feeds on algae
And Tusk Shells – shell like an elephant’s tusk, burrows in sand or mud and catches
particles of food with tiny tentacles
16. Mud Snails
Review rules for handling animals
Instruct students to look for foot, siphon tube, tentacles, eyes, operculum, mouth, and
radula.
17. References
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