Biology
Slide
1 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Slide
2 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
What Is a Mollusk?
What are the defining features of
mollusks?
Slide
3 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
What Is a Mollusk?
What Is a Mollusk?
Mollusks are soft-bodied animals that
usually have an internal or external shell.
Mollusks include snails, slugs, clams, squids,
and octopi.
Many mollusks share similar developmental
stages.
Slide
4 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
What Is a Mollusk?
Many aquatic mollusks
have a free-swimming
larval stage called a
trochophore.
The trochophore larva is
also characteristic of
annelids, indicating that
these two groups may
be closely related.
Slide
5 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Form and Function in Mollusks
Mollusks have complex, interrelated organ
systems that function together to maintain the body
as a whole.
Slide
6 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
What is the basic body plan of mollusks?
Slide
7 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Body Plan
The body plan of most mollusks has four
parts: foot, mantle, shell, and visceral
mass.
Slide
8 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
The muscular foot takes many forms
• flat structures for crawling
• spade-shaped structures for
burrowing
• tentacles for capturing prey
Squid
Snail
Clam
Copyright Pearson Prentice Hall
Slide
9 of 43
End Show
27-4 Mollusks
Form and Function in Mollusks
The mantle is a thin layer of tissue that covers most
of the mollusk's body.
The shell is made by glands in the mantle that
secrete calcium carbonate.
Just beneath the mantle is the visceral mass, which
contains the internal organs.
Slide
10 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Feeding
Mollusks can be herbivores, carnivores, filter
feeders, detritivores, or parasites.
Slide
11 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Snails and slugs feed
using a flexible, tongueshaped structure known
as a radula.
Hundreds of tiny teeth are
attached to the radula.
The radula is used to
scrape algae off rocks or
to eat the soft tissues of
plants.
Teeth
Radula
Slide
12 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Clams, oysters, and scallops use gills.
Food is carried by water, which enters the incurrent
siphon.
A siphon is a tubelike structure through which water
enters and leaves the body.
Slide
13 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
The water flows over the gills and leaves by the
excurrent siphon.
Excurrent
siphon
Incurrent
siphon
Slide
14 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Respiration
Aquatic mollusks breathe using
gills inside their mantle cavity.
Gills
Slide
15 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
As water passes through the mantle cavity,
oxygen in the water moves into blood flowing
through the gills.
At the same time, carbon dioxide moves in the
opposite direction.
Slide
16 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Land snails and slugs respire using a mantle cavity
that has a large surface area lined with blood
vessels.
Slide
17 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Circulation
Some mollusks have open circulatory systems;
other mollusks have closed circulatory systems.
Slide
18 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
In an open circulatory system, blood is pumped
through vessels by a simple heart.
Heart
Slide
19 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Blood leaves the vessels and works its way through
different sinuses.
Blood passes from the sinuses to the gills, where
oxygen and carbon dioxide are exchanged. Blood is
then pumped back to the heart.
Slow-moving mollusks often have open circulatory
systems.
Slide
20 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Faster-moving mollusks have a closed circulatory
system.
A closed circulatory system can transport blood
through an animal’s body much more quickly than an
open circulatory system.
Slide
21 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Excretion
Cells of the body release nitrogen-containing
waste into the blood in the form of ammonia.
Slide
22 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Nephridia remove ammonia from the blood and
release it outside the body.
Nephridium
Slide
23 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Response
The complexity of the nervous system and the
ability to respond to environmental conditions
varies among mollusks.
Two-shelled mollusks have a simple nervous
system.
Slide
24 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Octopi and their relatives have the most highly
developed nervous system of all invertebrates.
Well-developed brains in these animals allows them
to remember things for long periods.
Slide
25 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Movement
Snails secrete mucus along the base of the foot,
and then move over surfaces using a rippling
motion of the foot.
The octopus draws water into the mantle cavity
and then forces the water out through a siphon.
Water leaving the body propels the octopus in the
opposite direction.
Slide
26 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Form and Function in Mollusks
Reproduction
Some mollusks reproduce sexually by external
fertilization.
In other mollusks, fertilization takes place inside
the body of the female.
Some mollusks are hermaphrodites and usually
fertilize eggs from another individual.
Slide
27 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
What are the characteristics of the three
main classes of mollusks?
Slide
28 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
Groups of Mollusks
The three major classes of mollusks are
• gastropods
• bivalves
• cephalopods
Slide
29 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
Gastropods
Gastropods are shell-less or singleshelled mollusks that move by using a
muscular foot located on the ventral
side.
Many gastropods have a single shell that
protects their bodies.
When threatened, they can pull completely
into their shells.
Copyright Pearson Prentice Hall
Slide
30 of 43
End Show
27-4 Mollusks
Groups of Mollusks
Gastropods include
•
•
•
•
•
•
pond snails
land slugs
sea butterflies
sea hares
limpets
nudibranchs
Slide
31 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
Bivalves
Bivalves have two shells that are held
together by one or two powerful muscles.
Common bivalves include:
• clams
• oysters
• mussels
• scallops
Slide
32 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
Cephalopods
Cephalopods are typically soft-bodied
mollusks in which the head is attached to a
single foot. The foot is divided into
tentacles or arms.
Slide
33 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
Cephalopods have eight or more tentacles equipped
with sucking disks that grab and hold prey.
Most modern cephalopods have only small internal
shells or no shells at all.
The only present-day cephalopods with external
shells are nautiluses.
Slide
34 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Groups of Mollusks
Cephalopods have complex sense organs that help
them detect and respond to external stimuli.
Cephalopods distinguish shapes by sight and texture
by touch.
The eyes of many cephalopods are complex.
Slide
35 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Ecology of Mollusks
Ecology of Mollusks
Mollusks
• feed on plants
• prey on animals
• filter algae out of the water
• eat detritus
Slide
36 of 43
Copyright Pearson Prentice Hall
End Show
27-4 Mollusks
Ecology of Mollusks
Some mollusks are hosts to symbiotic algae or to
parasites; others are themselves parasites.
Mollusks are food for many organisms.
Slide
37 of 43
Copyright Pearson Prentice Hall
End Show
27-4
Click to Launch:
Continue to:
- or -
Slide
38 of 43
End Show
Copyright Pearson Prentice Hall
27-4
The trochophore larva is a characteristic that
mollusks share with
a. flatworms.
b. roundworms.
c. annelids.
d. flukes.
Slide
39 of 43
End Show
Copyright Pearson Prentice Hall
27-4
Water enters and leaves the body of a bivalve
through
a. a siphon.
b. cilia.
c. a coelom.
d. a nephridium.
Slide
40 of 43
End Show
Copyright Pearson Prentice Hall
27-4
The most active group of mollusks is the
a. gastropods.
b. bivalves.
c. cephalopods.
d. shell-less gastropods.
Slide
41 of 43
End Show
Copyright Pearson Prentice Hall
27-4
Unlike the other mollusks, cephalopods have
a(an)
a. closed circulatory system.
b. ventral blood vessel.
c. open circulatory system.
d. dorsal blood vessel.
Slide
42 of 43
End Show
Copyright Pearson Prentice Hall
27-4
The body plan of most mollusks includes all of
the following EXCEPT a
a. foot.
b. mantle.
c. shell.
d. radula.
Slide
43 of 43
End Show
Copyright Pearson Prentice Hall
END OF SECTION