Transcript Chapter 27 BDOL IC

Unit 1: What is Biology?
Unit 2: Ecology
Unit 3: The Life of a Cell
Unit 4: Genetics
Unit 5: Change Through Time
Unit 6: Viruses, Bacteria, Protists, and Fungi
Unit 7: Plants
Unit 8: Invertebrates
Unit 9: Vertebrates
Unit 10: The Human Body
Unit 1: What is Biology?
Chapter 1: Biology: The Study of Life
Unit 2: Ecology
Chapter 2: Principles of Ecology
Chapter 3: Communities and Biomes
Chapter 4: Population Biology
Chapter 5: Biological Diversity and Conservation
Unit 3: The Life of a Cell
Chapter 6: The Chemistry of Life
Chapter 7: A View of the Cell
Chapter 8: Cellular Transport and the Cell Cycle
Chapter 9: Energy in a Cell
Unit 4: Genetics
Chapter 10: Mendel and Meiosis
Chapter 11: DNA and Genes
Chapter 12: Patterns of Heredity and Human Genetics
Chapter 13: Genetic Technology
Unit 5: Change Through Time
Chapter 14: The History of Life
Chapter 15: The Theory of Evolution
Chapter 16: Primate Evolution
Chapter 17: Organizing Life’s Diversity
Unit 6: Viruses, Bacteria, Protists, and Fungi
Chapter 18: Viruses and Bacteria
Chapter 19: Protists
Chapter 20: Fungi
Unit 7: Plants
Chapter 21:
Chapter 22:
Chapter 23:
Chapter 24:
What Is a Plant?
The Diversity of Plants
Plant Structure and Function
Reproduction in Plants
Unit 8: Invertebrates
Chapter 25: What Is an Animal?
Chapter 26: Sponges, Cnidarians, Flatworms, and
Roundworms
Chapter 27: Mollusks and Segmented Worms
Chapter 28: Arthropods
Chapter 29: Echinoderms and Invertebrate
Chordates
Unit 9: Vertebrates
Chapter 30: Fishes and Amphibians
Chapter 31: Reptiles and Birds
Chapter 32: Mammals
Chapter 33: Animal Behavior
Unit 10: The Human Body
Chapter 34: Protection, Support, and Locomotion
Chapter 35: The Digestive and Endocrine Systems
Chapter 36: The Nervous System
Chapter 37: Respiration, Circulation, and Excretion
Chapter 38: Reproduction and Development
Chapter 39: Immunity from Disease
Invertebrates
What Is an animal?
Sponges, Cnidarians, Flatworms, and
Roundworms
Mollusks and Segmented Worms
Arthropods
Echinoderms and Invertebrate Chordates
Chapter 27 Introduction: Mollusks an Segmented
Worms
27.1: Mollusks
27.1: Section Check
27.2: Segmented Worms
27.2: Section Check
Chapter 27 Summary
Chapter 27 Assessment
What You’ll Learn
You will distinguish among the classes
of mollusks and segmented worms.
You will compare and contrast the
adaptations of mollusks and segmented
worms.
Section Objectives:
• Identify the characteristics of mollusks.
• Compare the adaptations of gastropod,
bivalve, and cephalopod mollusks in their
biomes.
What is a mollusk?
• Slugs, snails, squids, and some animals that
live in shells in the ocean or on the beach are
all mollusks. These organisms belong to the
phylum Mollusca.
• Although most
species live in the
ocean, others live in
freshwater and moist
terrestrial habitats.
What is a mollusk?
• Some mollusks have shells, and others,
including slugs and squids, are adapted to
life without a hard covering.
What is a mollusk?
• All mollusks have bilateral symmetry, a
coelom, a digestive tract with two openings,
a muscular foot, and a mantle.
Arm
Head
Tentacle
Visceral mass
Mantle
Reduced internal shell
Mantle
Gut
Shell
Foot
Squid
What is a mollusk?
• The mantle (MAN tuhl) is a membrane that
surrounds the internal organs of the mollusk.
In shelled mollusks, the mantle secretes the
shell.
Mantle
Snail
Shell
Gut
Head
Visceral mass
Mantle
Shell
Foot
Foot
How mollusks obtain food
• Snails, like many
mollusks, use a
rasping structure
called a radula to
obtain food.
• A radula (RA juh luh), located within the
mouth of a mollusk, is a tonguelike organ
with rows of teeth. The radula is used to
drill, scrape, grate, or cut food.
Radula
How mollusks obtain food
• Octopuses and squids are predators that use
their radulas to tear up the food that they
capture with their tentacles.
• Other mollusks are grazers and some are
filter feeders.
How mollusks obtain food
• Bivalves do not have radulas; they filter food
from the water.
Reproduction in mollusks
• Mollusks reproduce sexually and most have
separate sexes.
• In most aquatic species, eggs and sperm are
released at the same time into the water,
where external fertilization takes place.
• Many gastropods that live on land, and
a few bivalves, are hermaphrodites and
produce both eggs and sperm.
Fertilization is internal.
Reproduction in mollusks
• Some marine mollusks
have free swimming larvae
that propel themselves.
• Most marine snails and
bivalves have another
developmental stage called
a veliger in which he
beginnings of a foot, shell,
and mantle can be seen.
Nervous control in mollusks
• Molusks have simple nervous systems
that coordinate their movement and
behavior.
• Some more advanced mollusks have a
brain.
Nervous control in mollusks
• Most mollusks have
paired eyes that
range from simple
cups that detect
light to the complex
eyes of octopuses
that have irises,
pupils, and retinas
similar to the eyes
of humans.
Circulation in mollusks
• Mollusks have a well-developed circulatory
system that includes a three-chambered
heart.
Heart
Circulation in mollusks
• In most mollusks, the heart pumps blood
through an open circulatory system.
• In an open circulatory system, the blood
moves through vessels and into open spaces
around the body organs.
Circulation in mollusks
• Some mollusks, such as octopuses, move
nutrients and oxygen through a closed
circulatory system.
• In a closed circulatory system, blood moves
through the body enclosed entirely in a series
of blood vessels.
Respiration in mollusks
• Most mollusks have respiratory structures
called gills.
• Gills are specialized parts of the mantle that
consist of a system of filamentous
projections that contain a rich supply of
blood for the transport for gases.
Excretion in mollusks
• Mollusks are the oldest known animals to
have evolved excretory structures called
nephridia.
• Nephridia (nih FRIH dee uh) are organs that
remove metabolic wastes from an animal’s
body.
• Mollusks have one or two nephridia that
collect wastes from the coelom, which is
located around the heart only.
Excretion in mollusks
• Wastes are discharged into the mantle cavity,
and expelled from the body by the pumping
of the gills.
Diversity of Mollusks
• Phylum Mollusca is large and diverse.
• Three mollusk classes—Gastropoda,
Bivalvia, and Cephalopoda—include the
most common and well- known species.
Gastropods: One-shelled mollusks
• The largest class of mollusks is Gastropoda,
or the stomach-footed mollusks.
• The name
comes from the
way the
animal’s large
foot is
positioned
under the rest
of its body.
Gastropods: One-shelled mollusks
• Shelled gastropods include snails, abalones,
conches, periwinkles, whelks, limpets,
cowries, and cones.
• Instead of being protected by a shell, the
body of a slug is protected by a thick layer of
mucus.
Gastropods: One-shelled mollusks
• Colorful sea
slugs, also
called
nudibranchs,
are protected
in another
way.
Gastropods: One-shelled mollusks
• When certain species of sea slugs feed on
jellyfishes, they incorporate the poisonous
nematocysts of the jellyfish into their own
tissues without causing these cells to
discharge.
• Any fishes trying to eat the sea slugs are
repelled when the nematocysts discharge into
the unlucky predator.
Bivalves: Two-shelled mollusks
• Two-shelled
mollusks such as
clams, oysters, and
scallops belong to
the class Bivalvia.
• Most bivalves are
marine, but a few
species live in
freshwater habitats.
Bivalves: Two-shelled mollusks
• Bivalves have no distinct head or radula.
Most use their large, muscular foot for
burrowing in the mud or sand at the bottom
of the ocean or a lake.
• A ligament, like a hinge,
connects their two
shells, called valves;
strong muscles allow the
valves to open and close
over the soft body.
Bivalves: Two-shelled mollusks
• One of the main differences between
gastropods and bivalves is that bivalves are
filter feeders that obtain food by filtering
small particles from the surrounding water.
• Gill cilia beat to draw water in through an
incurrent siphon.
• As water moves over the gills, food and
sediments become trapped in mucus.
Bivalves: Two-shelled mollusks
• Cilia that line the gills push food particles to
the mouth.
• Large particles, sediment, and anything else
that is rejected is transported to the mantle
where it is expelled through the excurrent
siphon, or to the foot, where it is eliminated
from the animal’s body.
Cephalopods: Head-footed mollusks
• This class includes the octopus, squid,
cuttlefish, and chambered nautilus.
• The only cephalopod with a shell is the
chambered nautilus, but some species, such
as the cuttlefish, have a reduced internal
shell.
Cephalopods: Head-footed mollusks
• In cephalopods, the foot has evolved into
tentacles with suckers, hooks, or adhesive
structures.
• Cephalopods swim
or walk over the
ocean floor in
pursuit of their prey,
capturing it with
their tentacles.
Cephalopods: Head-footed mollusks
• Once tentacles have captured prey, it is
brought to the mouth and bitten with
beaklike jaws.
• Then the food is torn and pulled into the
mouth by the radula.
Cephalopods: Head-footed mollusks
• Cephalopods have siphons that expel water.
• These mollusks can expel water forcefully in
any direction, and move quickly by jet
propulsion. Squids can attain speed of 20m
per second using this system of movement.
Direction of squid
Water in
Water out
Cephalopods: Head-footed mollusks
• Squids and octopuses also can release a
dark fluid to cloud the water.
• This “ink” helps to confuse their
predators so they can make a quick
escape.
Question 1
Which of the following mollusks does
NOT have a radula, and why?
A. octopus
B. sea snail
C. clam
D. slug
The answer is C. Clams are filter feeders
that do not need a radula to obtain food.
Question 2
Which of the following is NOT a function
of the tentacles of a land snail?
A. smelling
B. feeling
C. moving the eyes
D. capturing prey
The answer is D, capturing prey.
Question 3
Which are the first mollusks you would
expect to be affected by pollution and why?
A. clams
B. snails
C. octopuses
D. squid
The answer is A. Clams are filter feeders.
They would be most likely to ingest plankton
and become polluted. Later, other mollusks
like sea snails that prey on clams might ingest
the same pollutant when they eat the clams.
Question 4
Nephridia are organs used for _____.
A. circulation
B. respiration
C. movement
D. excretion
The answer is D, excretion.
Section Objectives:
• Describe the characteristics of segmented
worms and their importance to the survival of
these organisms.
• Compare and contrast the classes of
segmented worms.
What is a segmented worm?
• Segmented worms are classified in the
phylum Annelida. They include leeches and
bristleworms as well as earthworms.
• Segmented worms are bilaterally symetrical
and have a coelom and two body openings.
What is a segmented worm?
• The basic body plan of segmented worms is
a tube within a tube.
• The internal tube, suspended within the
coelom, is the digestive tract.
What is a segmented worm?
• Food is taken in by
the mouth, an
opening in the
anterior end of the
worm, and wastes
are released
through the anus,
an opening at the
posterior end.
What is a segmented worm?
• Most segmented worms
have tiny bristles called
setae (SEE tee) on each
segment.
• The setae help segmented
worms move by providing a
way to anchor their bodies in
the soil so each segment can
move the animal along.
Setae
Segmentation supports diversified
functions
• The most distinguishing characteristic of
segmented worms is their cylindrical bodies
that are divided into ringed segments.
• In most species, this
segmentation continues
internally as each
segment is separated
from the others by a
body partition.
Segmentation supports diversified
functions
• Each segment has its own muscles, allowing
shortening and lengthening of the body.
• Segmentation also allows for specialization
of body tissues.
• Certain segments have modifications for
functions such as sensing and reproduction.
Nervous system
• Segmented worms have simple nervous
systems in which organs in anterior segments
have become modified for sensing the
environment.
• Some sensory organs are sensitive to light,
and eyes with lenses and retinas have
evolved in certain species.
Nervous system
• In some species there is a brain
located in an anterior segment.
• Nerve cords
connect the
brain to nerve
centers called
ganglia, located
in each
segment.
Setae
Gizzard
Aortic arches
Brain
Nerve
Intestine
Esophagus
Crop
Mouth
Circulation and respiration
• Segmented worms have a closed circulatory
system.
• Blood carrying oxygen to and carbon dioxide
from body cells flow through vessels to
reach all parts of the body.
• Segmented worms must live in water or in
wet areas on land because they also
exchange gases directly through their
moist skin.
Digestion and excretion
• Segmented worms have a complete internal
digestive tract that runs the length of the
body.
• Food and soil taken in by the mouth
eventually pass to the gizzard.
Digestion and
excretion
• In the gizzard,
a muscular
sac and hard
particles help
grind soil and
food before
they pass into
the intestine.
Crop
Mouth
Gizzard
Digestion and excretion
• Undigested material and
solid wastes pass out the
worm’s body through the
anus.
• Segmented worms have two
nephridia in almost every
segment that collect waste
products and transport them
through the coelom and out of
the body.
Nephridia
Section questions
1.
2.
3.
4.
5.
6.
Give three examples of segmented worms?
What are the tiny bristles called that aid the worm to anchor itself to
ground?
What is the distinguishing feature of segmented worms?
What are the nerve centers called that connect the nerve cord to brain?
What kind of circulatory system to segmented worms have?
What is the gizzard and what is its function?
Reproduction in segmented worms
• Earthworms and leeches are hermaphrodites,
producing both eggs and sperm.
• During mating, two worms exchange sperm.
• Each worm forms a capsule for the eggs and
sperm.
Reproduction in segmented worms
• The eggs are fertilized in the capsule, then
the capsule slips off the worm and is left
behind in the soil.
• In two to three weeks, young worms emerge
from the eggs.
Reproduction in segmented worms
• Bristleworms and their relatives have
separate sexes and reproduce sexually.
Reproduction in segmented worms
• Usually eggs and sperm are released into the
seawater, where fertilization takes place.
• Bristleworm larvae hatch in the sea and
become part of the plankton.
• Once segment development begins, the
worm settles to the bottom.
Diversity of Segmented Worms
• The phylum Annelida includes three classes:
class Oligochaeta, earthworms; class
Polychaeta, bristleworms and their relatives;
and class Hirudinea, leeches.
Earthworms
• Earthworms are the most well-known
annelids because they can be seen easily by
most people.
• As an earthworm burrows through soil, it
loosens, aerates, and fertilizes the soil.
Gizzard
Mouth
Crop
Setae
Circulatory
system
Nephridia
Earthworms
Nervous
system
Bristleworms and their relatives
• The class Polychaeta includes bristleworms
and their relatives—fanworms, lug worms,
plumed worms, and sea mice.
Bristleworms and their relatives
• Most body segements of a polychaete have
many setae, hence the name. Polychaete
means “many bristles”.
• Most body segments of a polychaete also
have a pair of appendages called parapodia,
which can be used for swimming or crawling
over corals and the bottom of the sea.
Bristleworms and their relatives
• Parapodia also function in gas exchange.
• A polychaete has a head with well-developed
sense organs, including eyes.
Leeches
• Leeches are segmented worms with flattened
bodies and usually no setae.
• Unlike earthworms, many species are
parasites that suck blood or other body fluids
from the bodies of their hosts, which include
ducks, turtles, fishes, and humans.
Leeches
• Front and rear suckers enable leeches to
attach themselves to their hosts.
Leeches
• The saliva of the leech contains chemicals
that act as an anesthetic.
• Other chemicals prevent the blood from
clotting.
• A leech can ingest two to five times its own
weight in one meal.
Origins of Mollusks and Segmented
Worms
• Fossil records show that mollusks lived in
great numbers as long as 500 million years
ago.
• Gastropod, bivalve, and cephalopod fossils
have been found in Precambrian deposits.
Origins of Mollusks and Segmented Worms
• Annelids probably evolved in the sea,
perhaps from larvae of ancestral flatworms.
Origins of Mollusks and Segmented
Worms
• Tubes constructed by polychaetes are the
most common fossils of this phylum.
• Some of these tubes appear in the fossil
record as early as 540 million years ago.
Question 1
Why must segmented worms live in a
moist environment?
Answer
Segmented worms must live in or near water
because they exchange gases directly through
their moist skin.
Question 2
During mating, earthworms exchange _____.
A. eggs
B. sperm
C. capsules containing both sperm and eggs
D. larvae
The answer is B, sperm.
Question 3
Using this figure,
give the reason why
you would
determine this to be
the anterior end of
the organism?
4
5
6
7
8
9
10
11
12
13
14
15
16
3
2
1
Brain
Pharynx
Esophagus
Blood
vessel
Crop
Nephridia
The anterior portion of
an organism would
logically include the
brain, as well as the
initial parts of a gut, like
the esophagus and crop
(the esophagus and crop
are necessary to the
initial phases of
digestion).
4
5
6
7
8
9
10
11
12
13
14
15
16
3
2
1
Brain
Pharynx
Esophagus
Blood
vessel
Crop
Question 4
Which organism would likely get the
most use from a gizzard, an earthworm
or a leech?
Answer
A gizzard grinds organic matter into small
pieces so the nutrients in the food can be
absorbed. Since a leech’s food is liquid
(blood), the earthworm would use a gizzard
the most, to grind the food and soil it
ingests.
Question 5
Earthworms are considered to be ______.
A. predators
B. parasites
C. filter feeders
D. grazers
The answer is D, grazers.
Mollusks
• Mollusks have bilateral symmetry, a coelom,
and a digestive tract with two openings. Many
also have shells.
• Most gastropods, such as snails, have a shell,
mantle, radula, an open circulatory system,
gills, and nephridia. Gastropods without
shells, such as slugs, are protected by a
covering of mucus.
Mollusks
• Bivalve mollusks have paired shells, called
valves, and are filter feeders. They have no
radula. Clams and scallops are bivalves.
• Cephalopods have tentacles with suckers,
beaklike jaws, a mouth with a radula, and a
closed circulatory system. Cephalopods
include the octopus, squid, and chambered
nautilus.
Segmented Worms
• The phylum Annelida includes the
earthworms, bristleworms, and their relatives,
and leeches. Annelida are bilaterally
symmetrical and have a coelom and two body
openings; some have larvae that look like the
larvae of mollusks. Their bodies are
cylindrical and segmented.
• Earthworms have complex digestive,
excretory, muscular, and circulatory systems.
Segmented Worms
• Bristleworms and their relatives are mostly
marine species. They have many setae and
parapodia that are used for crawling along.
• Leeches are flattened, segmented worms.
Most are aquatic parasites.
• Fossil remains of mollusks show that they
first lived over 500 million years ago. Fossil
records show that segmented worms first
appeared 540 million years ago.
Question 1
With the exception of slugs, all mollusks that
are slow-moving or sessile have shells.
Why?
Shells provide
organisms with a
place to hide that is
always near them,
since they cannot
quickly escape a
predator.
Question 2
Why is a closed circulatory system more
efficient than an open circulatory system?
A closed circulatory system is more efficient
because blood is transported entirely in closed
vessels that can reach deep into the organism’s
tissues and provide efficient gas exchange. In
an open circulatory system, tissues farthest
from the open spaces containing blood are not
so likely to be reached for efficient gas
exchange.
Question 3
Why do scientists consider cephalopods to be
the most recently evolved of all mollusks?
Answer
Cephalopods possess the most complex
structures of all mollusks, such as complex
eyes, complex brains, closed circulatory
systems and feet that have evolved into
complex structures like arms and tentacles.
Question 4
Why are mollusks considered to be excellent
index fossils?
Answer
Mollusks are generally well preserved in the
fossil record, abundant, easy to recognize, and
widely distributed geographically.
Question 5
Which of the following is NOT a food source
for humans and why?
A. abalones
B. octopuses
C. ammonites
D. conches
The answer is C. Ammonites are not a food
source for any organism, because they are
extinct.
Question 6
How does a leech benefit from the chemicals
in its saliva that prevent clots from forming?
Answer
Preventing blood clots keeps a free flow of
blood available to the leech until it is done
feeding.
Question 7
What is the function of parapodia?
Answer
Polychaetes use parapodia for swimming,
crawling, and for gas exchange.
Question 8
Why do annelids have such a limited fossil
record?
Answer
The fossil record for segmented worms is
limited because segmented worms have almost
no hard body parts from which fossils could
develop.
Question 9
What is the function of setae?
Answer
Setae help segmented worms move by
providing a way to anchor their bodies in the
soil so each segment can move the animal
along.
Question 10
Which of the following features do annelids
NOT share with mollusks?
A. coelom
B. bilateral symmetry
C. digestive tract with two openings
D. segmented bodies
The answer is D, segmented bodies.
Photo Credits
• General Biololgical Inc.
• Digital Stock
• Joey Jacques
• Corbis
• PhotoDisc
• Alton Biggs
To advance to the next item or next page click on any of the
following keys: mouse, space bar, enter, down or forward
arrow.
Click on this icon to return to the table of contents
Click on this icon to return to the previous slide
Click on this icon to move to the next slide
Click on this icon to open the resources file.
End of Chapter 27 Show