Phylum MolluscaPhylum Mollusca

Chapter 13: Phylum Molluscapp. 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 MolluscsIntroduction to MolluscsMolluscs 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?Where do Molluscs fit in?

Introduction to MolluscsIntroduction to MolluscsPhylum Mollusca – Latin molluscus = “soft”ProtostomesBilateral symmetry; eucoelomates3 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 MolluscsIntroduction to MolluscsMolluscs all share similar developmental patterns and a common body plan: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 MolluscsClasses 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 MolluscsClasses of Molluscs3) 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 threatenedExample members: octopus, squid, nautilus, cuttlefish

Octopus

Nautilus

Squid

Squid are the largest Squid are the largest CephalopodsCephalopods

Colour and Morphology Colour and Morphology Changes = CamouflageChanges = Camouflage

Form and Function of Form and Function of MolluscsMolluscsMolluscs vary a lot clam = representative molluskDigestive 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 Form and Function of MolluscsMolluscsRespiratory 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 MolluscsEcology of MolluscsBivalves used to check pollution levels –

“environmental monitors”

Range of lifestyles: predators, scavengers, filter feeders, etc.

Crop damage – slugs, snails on land

Ship damage – shipworms in water

Food source for humans: clams, oysters, mussels, etc.

• Humans can get poisoned by eating mollusks contaminated with toxic protists cause “red tide”

Molluscs Movie!Molluscs Movie!

Mollusc (5-7-5) Haiku: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 CitedWorks CitedImages taken from the following

sources:http://other95.blogspot.com/2007/10/circus-of-

spineless-26-like-being-home.htmlhttp://offthemark.com/search-results/key/mollusk/http://kevinmainjewelry.blogspot.com/2010/06/pearl-fun-facts-and-care-tips.htmlhttp://seashellvilla.com/advertise_here.htmlhttp://www.zazzle.com/snail_mail_postcard-239469706654312651http://bio1151b.nicerweb.com/Locked/media/ch32/trochophore.htmlhttp://www.education.com/study-help/article/biology-help-mollusks-clam-up-would-ya/

Works CitedWorks Citedhttp://www.thecanadianencyclopedia.com/index.cfm?PgNm=TCESearchMedia&Params=A1&MediaId=385http://perfectgardeningtips.com/category/plants/pest-control/http://www.apartmenttherapy.com/sf/insects-pests/slugs-082896http://birdhouse.org/blog/2008/05/16/nudibranchs/http://www.zazzle.com/i_squid_cephalopods_tshirt-235319078835508111https://www.mentalfloss.com/blogs/archives/58856http://radio-weblogs.com/0105910/2004/01/10.htmlhttp://ihatetheocean.blogspot.com/2010/08/august-6-2010-nautilus.htmlhttp://zollberg.co.cc/bivalve.html

Works CitedWorks Citedhttp://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/mollusk-classification-choose?commentId=2223964%3AComment%3A10692&xg_source=activity

http://sharon-taxonomy2009-p3.wikispaces.com/Mollusca

http://www.lifeinfreshwater.org.uk/Web%20pages/ponds/Pollution.htm

http://www.nero.noaa.gov/nero/hotnews/redtide/

http://www.sheppardsoftware.com/content/animals/profile_mollusks.htm