Transcript 01 Mollusca - Mr. Harshenin

Phylum Mollusca
Chapter 13: Phylum Mollusca
pp. 329-334
Biology fun facts
of the day:
Experts claim that
about 1,000 oysters
must be opened in
order to find one
usable pearl!
Biology fun facts
of the day:
The common garden snail, Helix
aspersa, can travel about 2 feet
in 3 minutes. At that rate, it
would travel 1 mile in 5.5 days.
(Now you know where the term
‘snail mail’ comes from!)
Biology fun facts
of the day:
When we hold a large seashell up to
our ear, you can hear what sounds
like waves because the shell echoes
all the sounds around you.
If you could listen to a shell in a
completely soundproof room, you
would hear nothing at all!
Biology fun facts
of the day:
Many land snails can lift 10 times
their own weight up a vertical
surface. (If you were this strong,
and you weighed 30 kg (about 70 lb),
you could carry 300 kg (almost 700
pounds!!!) straight up a wall!
Introduction to Molluscs
Molluscs represent the second largest animal phylum,
following the arthropods
= Old Phylum (500 million years, approx.)
80,000 – 100,000 existing species (estimate)
Most species are free-living
Inhabit a variety of marine, aquatic & terrestrial habitats
Important ecological roles with regards to nutrient recycling;
bivalves clean and recycle sediments
Empty shells provide habitat for other invertebrates
Where do Molluscs fit in?
Introduction to Molluscs
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Phylum Mollusca – Latin molluscus = “soft”
Protostomes
Bilateral symmetry; eucoelomates
3 cell layers (ectoderm, endoderm, mesoderm)
Have a coelom (but often reduced to a cavity that
surrounds only the heart)
Have trochophore larvae (free-swimming ciliated larva)
• Similar larvae in annelids 
likely share a common ancestor
Introduction to Molluscs
Molluscs all share similar developmental patterns and
a common body plan:
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Foot (muscle; function varies)
Shell (protection; made of CaCO3)
Mantle (produces the shell)
Visceral mass (contains internal organs)
Diagrams of
snail, clam, and
squid p. 300
Classes of Molluscs
1) Class Bivalvia
• 2 hinged shells
• No head or eyes
• Gills; live in water
Example members: clams, oysters, scallops
2) Class Gastropoda
• One shell
• Some are terrestrial
Example members: snails, slugs, nudibranchs
Classes of Molluscs
3) Class Cephalopoda
 Fast-moving predators
 Foot is modified into tentacles
 Well-developed nervous system
 Some can use camouflage and jet propulsion (e.g.
octopus) when they feel threatened
Example members: octopus, squid, nautilus, cuttlefish
Nautilus
Octopus
Squid
Squid are the largest Cephalopods
Colour and Morphology Changes =
Camouflage
Form and Function of Molluscs
Molluscs vary a lot  clam = representative mollusk
Digestive system:
• Complete digestive tract (mouth  anus)
• Mouth, esophagus, stomach, intestine, anus
• Have a radula (scraping/drilling organ) or a beak
(cephalopods)
• Bivalves trap food in their gills – no radula
e.g. Gastropod
Form and Function of Molluscs
Respiratory system:
• Aquatic mollusks have gills
• Terrestrial mollusks have a highly folded mantle for
O2/CO2 exchange (must stay moist)
*A clam has incurrent and excurrent siphons  sea water passes
through; location of gas exchange
Circulatory system:
• Open circulatory system – the heart pumps blood
through open spaces called sinuses instead of
through blood vessels
Excretory system:
• Nephridia (primitive kidneys) remove metabolic
waste (nitrogen-containing wastes like NH3)
• Digestive wastes go out anus
Nervous system:
• Bivalves – reduced nervous system; no head
• Gastropods – fairly basic
• Cephalopods – very well developed
• Good vision, small ganglia near mouth, statocysts
(balance), simple chemical and touch receptors
• Good dexterity and memory – they can learn!
Musculoskeletal system:
• Muscular foot for movement
• Bivalves – “two shell”; foot pulls animal forward,
and can be sucked back in (for protection)
• Gastropods – “stomach foot”; they slide forward
on broad ventral foot (use muscus)
• Cephalopods – “head foot”; foot has been
modified into many tentacles with suction cups
e.g. Gastropod
Reproduction:
• Some Monoecious (have both sex organs, capable of
producing both sperm and eggs)
• Others are Dioecious (either male or female gonads,
can produce one type of gamete only)
• Separate sexes (usually)
• External fertilization (broadcast method) in
bivalves/marine gastropods)  the female traps
sperm
• Internal fertilization in cephalopods/terrestrial
gastropods
Ecology of Molluscs
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Bivalves used to check pollution levels – “environmental
monitors”
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Range of lifestyles: predators, scavengers, filter feeders, etc.
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Crop damage – slugs, snails on land
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Ship damage – shipworms in water
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Food source for humans: clams, oysters, mussels, etc.
• Humans can get
poisoned by eating
mollusks contaminated
with toxic protists 
cause “red tide”
Molluscs Movie!
Mollusc (5-7-5) Haiku:
Slow, slick, sliding slug
Terrestrial explorer
No protective shield
Create your own mollusc haiku in 5-7-5 format!
Works Cited
Images taken from the following sources:
http://other95.blogspot.com/2007/10/circus-of-spineless26-like-being-home.html
http://offthemark.com/search-results/key/mollusk/
http://kevinmainjewelry.blogspot.com/2010/06/pearl-funfacts-and-care-tips.html
http://seashellvilla.com/advertise_here.html
http://www.zazzle.com/snail_mail_postcard239469706654312651
http://bio1151b.nicerweb.com/Locked/media/ch32/trocho
phore.html
http://www.education.com/study-help/article/biology-helpmollusks-clam-up-would-ya/
Works Cited
http://www.thecanadianencyclopedia.com/index.cfm?PgNm
=TCESearchMedia&Params=A1&MediaId=385
http://perfectgardeningtips.com/category/plants/pestcontrol/
http://www.apartmenttherapy.com/sf/insects-pests/slugs082896
http://birdhouse.org/blog/2008/05/16/nudibranchs/
http://www.zazzle.com/i_squid_cephalopods_tshirt235319078835508111
https://www.mentalfloss.com/blogs/archives/58856
http://radio-weblogs.com/0105910/2004/01/10.html
http://ihatetheocean.blogspot.com/2010/08/august-6-2010nautilus.html
http://zollberg.co.cc/bivalve.html
Works Cited
http://js082.k12.sd.us/My_Classes/Advanced_Biology/Ch_25
/Clam%20Dissection/Clam_Dissection.htm
http://www.sciencewithme.com/learn-about-mollusks/
http://www.bio.miami.edu/dana/106/106F06_12.html
http://nashzoology.ning.com/forum/topics/molluskclassificationchoose?commentId=2223964%3AComment%3A10692&x
g_source=activity
http://sharon-taxonomy2009-p3.wikispaces.com/Mollusca
http://www.lifeinfreshwater.org.uk/Web%20pages/ponds/Poll
ution.htm
http://www.nero.noaa.gov/nero/hotnews/redtide/
http://www.sheppardsoftware.com/content/animals/profile_
mollusks.htm