2. Structure
● soft bodied animals
○ name from Latin word "mollus" meaning soft
● most are protected by a hard shell made of
Calcium Carbonate
● have a reduced internal cell or have lost the
shell completely during evolution.
● possession of a coelom
○ coelom- a fluid-filled cavity that develops within the
mesoderm
3. Structure Cont.
● 3 distinct body zones:
○ Foot- contains sensory and motor organs
○ Visceral Mass- contains internal organs used for
digestion, excretion, and reproduction
○ Mantle- a fold of tissue that drapes over the visceral
mass and secretes a shell if there is one present
■ mantle cavity- water-filled chamber that houses
the gills, anus, and excretory pores.
● radula- straplike rasping organ used to
scrape up food with curved teeth
○ it allows the molluscs to scrape algae and other food
off of rocks and drill through the shell of prey or
catch fish
4.
5. Digestion and Excretion
● The digestive tract is complete and ciliated
with a mouth, anus, and complete stomach.
● Food is taken up by cells in the lining of the
stomach and passed into the blood
○ undigested materials are compressed and packaged
and discharged through the anus to the mantle
cavity and carried into the water currents.
● Excretory functions are carried out by a pair
of nephridia
○ nephridia- tubular structures that collect fluids from
coelom and exchange salts with body tissues as fluids
pass along the tublues.
6. Nervous System
● relatively complex
○ most complex- Octopus
● 2 pairs of main nerve cords
○ visceral- serve the internal organs
○ pedal-control the foot
● brain encircles the esophagus
● sensory ability
○ variety of organ systems
○ large, complex eyes
■ larges eyes- large squid(eyes the size of dinner
plates)
7.
8. Respiration and Circulation
● open circulatory system
○ the blood does not circulate entirely within vessels
but is collected by the gills, pumped into the heart,
and released in spaces in the tissue (hemocoel)and
returns to the gills, then the heart.
■ hemocoel- "blood cavity"
● Respiration pigment- hemocyanin
● Respiration is through gills, ctenidia, located
in the mantle cavity
9.
10. Reproduction
● sexual
● can by simple or very complex
○ varies in different classes
● fertilized egg develops into a swimming form
called a trochophore larva
● this then elongates to become a veliger larva
11. Locomotion
● varies, but is dictated by the structure of the
foot
● Herbivorous forms are gliders, moving on
waves of muscular contraction.
● Cephalopods swim actively by jet propulsion
in which water is rapidly expelled from the
mantle cavity.
● Cuttlefish and Sea Hares rely on lateral fins
for locomotion.
12.
13. Types
The three most common types
of mollusks are:
● gastropods
● bivalves
● cephalopods
14. Gastropoda
● Gastropods make up 80% of Molluscs
which consist of about 37,500
living species.
● Most gastropods have an external shell.
● They can either be herbivores, scavengers, and
carnivores.
● They usually live in oceans, on rocks and land, and in
freshwater.
● They use their muscular foot to
creep along a carpet of mucus that they
ooze out in order to crawl.
15. ● The most common gastropods are:
○ Snails - land and aquatic
○ Slugs
○ Nudibranchs
○ Pteropods - Thecosomata - sea butterflies
16.
17. Bivalvia
● Also known as Pelycopoda or Lam ellibranchia
● Bivalves always have two shells held together by hinges
and strong muscles.
● Some are omnivores (an animal or person that eats food
of both plant and animal origin) and also eat bacteria
and protists.
● They filter feed in which food sticks to the mucus on
their gill, then cilia move to their mouth.
● They may live in any watery environment because they
are able to swim and float around.
● They are the only type of molluscs that does not
have a radula.
18. ● Bivalves lack defined heads.
● Eyes may be present somewhere else on the body.
● They have an open circulatory system.
● They also have sensory cells.
● There are approximately 7,500 living species of bivalves.
● The name bivalves derives from their two valves, their
two shells in which it is divided.
● Most common bivalves include:
● Mussels
● Clams
● Oysters
● Scallops
19.
20. Cephalopoda
● Cephalopods either have internal shells,
external shells, or no shell at all.
● They are carnivores.
● They capture prey with their muscular tentacles,
crush it with their beak, and scrape the flesh off
with their radula.
● There are about 600 living species.
21. ● They all live in the ocean.
● They are able to move through jet propulsion
(squeezing a current of water out of their mantle
cavity and through a tube).
● Their closed circulatory system makes them the
fastest, smartest, and biggest of all molluscs.
● Some common cephalopods include:
○ Octopus
○ Squid
○ Cuttlefish
○ Nautilus
22. Importance of Molluscs
● Molluscs serve as food for humans as well as
for other animals.
● They are used for pearls and Native
American currencies.
● Some are used as environmental indicators
because their bodies are filled with water.
● There are about 85,000 species of molluscs.
● It is the largest marine phylum.
● There is a risk of food poisoning from toxins
that accumulate in moluscs.
● Their bites and stings are fatal and some are
venomous.
