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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:.

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phylum mollusca

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
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

introduction to molluscs1
Introduction to Molluscs
  • 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 molluscs2
Introduction to Molluscs

Molluscs 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 molluscs
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 molluscs1
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




form and function of molluscs
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 molluscs1
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 – theycan 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



  • 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
Ecology of Molluscs
  • Bivalves 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”
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 cited
Works Cited

Images taken from the following sources:

works cited1
Works Cited

works cited2
Works Cited