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Mollusca. Paul Ko Andy Zhao Michael Chiu Period 5. 4 Major Classes: Polyplacophora Bivalvia Gastropoda Cephalopoda.

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Paul Ko

Andy Zhao

Michael Chiu

Period 5

4 major classes polyplacophora bivalvia gastropoda cephalopoda
4 Major Classes:





Class Polyplacophora
  • Chiton
  • Marine
  • Shell with Eight Plates
  • Foot used for locomotion
  • Radula
  • No head



    • Clams and oysters
    • Sedentary or sessile filter-feeding
    • Marine and Freshwater or Terrestrial
    • Head reduced
    • Paired Gills
    • No radula



      • Aquatic and terrestrial snails and slugs
      • Marine, Freewater/terrestrial
      • Usually has a shell
      • Foot for locomotion
      • Radula



    • Predatory cuttlefish, squids and octopi.
    • Marine
    • Head surrounded by tentacles
    • Tentacles usually have suckers
    • External, internal or absent Shell
    • Mouth with or without radula

body cavities
Body Cavities

o The body cavities in Mollusca are called mantle cavities (coelom), which are:

  • Water-filled cavities that house the gills, anus, and
  • excretory pores.
  • There are also blood cavities known as hemocoel
  • which store blood in open-circulatory mollusca.
body symmetry
Body Symmetry
  • All mollusca have bilateral symmetry meaning…
  • The organism can be cut in half with the two sides looking more or less exactly the same.
  • Ex:

nervous system
Nervous System
  • Relatively complex nervous system, varies from species to species.
  • All Mollusca have tentacles that have sensors to detect chemicals, vibrations and touch.
  • Mollusca have ganglia, a sort of brain-like organ.

circulatory system
Circulatory System
  • Other than cephalopods, all Mollusca have an open circulatory system
  • These cavities are known as hemocoel, and in mollusks, it has replaced the coelem.
  • Cephalopods need a closed-circulatory system because their activities require more energy.

digestive system

Digestive System

Radula to scrape up food

Digestive tract is complete and ciliated

Includes mouth, anus and complex stomach

Food is taken up by the digestive glands arising from the stomach, where it is passed into the blood

excretory system
Excretory System
  • Waste is in solid form so it prevents the fouling of water over gills
  • Excretory functions are regulated by a pair of nephridia and tubular structures
  • Collect fluids from coleom and exchanges salts and substances with body tissues during excretion

locomotion musculature
  • Foot comprised of 3 main body parts
    • Viceral mass: contains interal organs
    • Mantle: fold of tissue over visceral mass, includes shell (if present
    • Mantle Cavity: houses gills and anus and excretory skills
  • Herbivores are commonly gliders, move on muscular contraction
  • Carnivores, more advanced locomotion
    • Cephalopods – Jet Propulsion
    • Cuttlefish/Sea Hares – Undulating later fins
    • Bivalves – Foot for burrowing

skeletal system
Skeletal System



They have shells made

of calcium carbonate

sensory structures features
Sensory Structures/Features
  • Some mollusks have large complex eyes (notably the cephalopods)
  • Squids can locate and capture transparent prey with specialized polarization vision.


  • Sexual Reproduction
  • External Fertilization: Sperm cell is united with egg cell away from the parents.
  • Trochophore = Larvae
  • Internal Fertilization

Example: Land snails are hermaphrodites. They have a pouch for holding the sperm of the mate.

gas exchange
Gas Exchange
  • Generally takes place

in the true gills (ctenidia)

  • Absorbs the Oxygen

from water and diffuses

Carbon Dioxide into the


unique features
Unique Features
  • Mantle: Encloses mantle cavity, which circulates oxygen and water.
  • Radula: The mouth, with teeth bent inwards. Ctenidia

Calcium Carbonate Shells

quiz questions

1. Which of the following phyla do not have symmetry?

a. Mollusca

b. Porifera

c. Echinodermata

2. Which of the following classes of Mollusca need a closed circulatory system?

a. Cephalopoda

b. Bivalvia

c. Gastropoda

d. Polyplacophora

quiz questions cont
Quiz Questions (Cont.)

3. Excretory functions are regulated by…

a. Nephridia b. Tubular structures

c. Both d. Neither

4. Land Snails reproduce…

a. Through internal fertilization

b. Through external fertilization

c. Sexually

d. Asexually

5. Why don't they serve escargots at a McDonald's restaurants?


1. b

2. a

3. d

4. a

5. They only serve fast food 


Thank You