Transcript Mollusks

Mollusks
Chapter 27
Facts and Fun
Flatworms
Are soft, flattened worms that have tissues
and internal organ systems.
 The simplest animals to have three
embryonic germ layers, bilateral
symmetry, and cephalization
 Three embryonic layers include: ectoderm,
endoderm, and mesoderm

Closer Look

Use Fig 27-3 to help you label the flatworm
WORD BANK
Nerve Cords
Pharynx
Ganglia
Digestive Cavity
Eyespot
Flatworms
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Form and function
 Feeding
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Free living flatworms feed on tiny aquatic animals or they can
be scavengers and feed on recently dead animals
 Respiration,
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Circulation, and Excretion
Do not need circulatory system because their body is thin
and flat
They rely on diffusion to transport oxygen and nutrients to
their internal tissues and to remove carbon dioxide and other
waste.
 Response
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Head encloses several ganglia or groups of nerve cells
Eyespot – group of cells that can detect changes in the
amount of light in their environment.
Flatworms
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Movement
 Move
two ways
Cilia – helps them glide through the water and
over the bottom of a stream or pond.
 Muscle cells – twist and turn to react to
environmental stimuli.
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Reproduction
 Reproduce
sexually and asexually
(Sexually) Hermaphrodite – an individual that has
both male and female reproductive organs.
 (Asexually) Fission – organism splits in two and
each half grows new parts to become a new
organism
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3 Groups of Flatworms
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Turbellarians
 Free
living
 Live in marine or fresh water under stones, shells,
sand, or mud
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Flukes
 Parasitic
 Infect
organs of their host
 Live in skin, mouth, gills, or other outside parts of the
host.

Tapeworms
 Long,
flat, parasitic
 Adapt to life inside the intestines of their host where
food is absorbed through their body walls.
 They have no digestive tract
Roundworms

Unsegmented worms that have
psedocoeloms and digestive systems with
two openings – a mouth and an anus.
Roundworms

Form and function
 Feeding
 Use grasping mouthparts and spines to catch and eat other
small animals.
 Some eat algae, fungi, or pieces of decaying organic matter
 Respiration, Circulation, and Excretion
 Exchange gases and excrete metabolic waste through their
body walls.
 They rely on diffusion to carry nutrients and waste through
their body.
 Response
 Several ganglia or groups of nerve cells
 Nerves that extend from the ganglia in the head and run the
length of the body.
 Sense organs that detect chemicals given off by prey or
hosts.
Roundworms
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Movement
 Muscles
that extend the length of their body
Aquatic – contract muscles to move like snakes
 Soil dwelling – push their way through soil by
thrashing around.
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Reproduction
 Reproduce
sexually
Have separate sexes – either male or female
 Use internal fertilization
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Pain and suffering in humans

4 human disease
1.
Trichinosis causing worms

2.
Adult worm live and mate in the intestines of the
host including humans, pigs, and other
mammals.
Filarial worms
Found in tropical regions
of Asia
 Threadlike worms that live in
blood or lymph vessels of birds
and mammals
 Transmitted through biting insects (mosquitoes)
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Pain and suffering in humans
3.
Ascarid worms
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4.
Found in humans and other vertebrate animals
Causes malnutrition in more than 1 million
people
Absorbs digested food from the host’s small
intestine.
Spreads by eating vegetables or other foods that
are not washed properly.
Hookworms
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Eggs hatch outside the body and develop in soil
Enters through an unprotected foot
Sucks the host’s blood causing weakness and
poor growth.
How are the eggs
released from the
body?
Through its feces
How do the worms get
back into the host
(dogs)?
Dog ingest the
larva/egg or by eating
the transport host
Eating undercooked
meat containing
larval cysts
Elephantiasis
Hookworms
Worms attach to intestinal
wall and suck blood,
causing weakness and
poor growth
Annelids
Worms with segmented bodies
 Have a true coelom that is lined with tissue
derived from mesoderm.

Annelids
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Form and function
 Feeding
Uses a pharynx that is covered with sticky mucus
 Pharynx holds two or more sharp jaws
 Feed on decaying vegetation

 Respiration
Aquatic – use gills to breathe
 Land dwelling – breathe through their moist skin
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 Circulation

Have a closed circulatory system – blood is
contained within a network of blood vessels
Annelids
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Movement
 Move
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by alternately contracting two sets of muscles
Longitudinal muscles – run from the front of the worm to the
rear and can contract to make the worm shorter and fatter.
Circular muscles – wrap around each body segment and
can contract to make the worm longer and thinner.
Reproduction
 Reproduce

sexually
Fertilization takes place in the clitellum – band of thickened
specialized segments, secretes a mucus ring into which
eggs and sperm are released.
Groups of Annelids
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Oligochaetes
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Leeches
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Contains earthworms and their relatives
Streamlined bodies
Live in soil or fresh water
Earthworm castings are a mixture of sand, clay, and undigested
food that an earthworm expels from its anus.
Parasites that suck blood and body fluids of their host.
Can be used to treat medical conditions
Polychaetes
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Marine annelids that have paired, paddlelike appendages tipped
with setae.
Live in cracks and crevices in coral reefs, in sand, mud, and
piles of rocks.
Section27–16
27-3
Figure
The Anatomy of an Earthworm
Anus
Setae
Body segments
Gizzard Crop
Dorsal
blood vessel
Clitellum
Mouth
Brain
Ganglion
Circular muscle
Longitudinal
muscle
Nephridia
Ganglia
Ring
vessels
Reproductive
organs
Ventral
blood vessel
Mollusks
Soft bodied animals that usually have an
internal and external shell.
 Include:
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Snails
Slugs
Clams
Squids
Octopus
Mollusks
Have a larval stage called trochophore.
Label:
A.__________________
B.__________________
C.__________________
D. _________________
Soft bodies
Mollusks
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Form and function
 Body
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Plan
Has four parts
Foot - flat structures for crawling, spade-shaped structures
for burrowing and tentacles for capturing prey.
Mantle – thin layer of tissue that covers most its body
Shell – made of glands in the mantle that secrete calcium
carbonate.
Visceral Mass – beneath the mantle, consists of the internal
organs.
Mollusks
 Feeding

Snails and slugs use a radula – tongue like structure to
which hundreds of tiny teeth are attached.
 Respiration
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Aquatic – use gills to breathe
Land dwelling – breathe using a mantle cavity that has a
large surface area lined with blood vessels.
 Circulation
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Have a open and closed circulatory system
Open circulatory system – blood is pumped through vessels
by a simple heart.
Octopi and squid have a closed circulatory system
Roundworms
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Movement
 Several
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methods
Snails – secrete mucus along the base of the foot and move
over surfaces using a rippling motion of the foot.
Octopi draws water into the mantle cavity and then forces
the water out through a siphon – a tubelike structure
through which water enters and leaves the body.
Reproduction
 Reproduce

sexually
Fertilization takes place in the clitellum – band of thickened
specialized segments, secretes a mucus ring into which
eggs and sperm are released.
Groups of Mollusks

Gastropods
 Shell
less or single shelled that move by using a
muscular foot located on the ventral side. Ex:Snail
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Bivalves
 Two
shells that are held together by one or two
powerful muscles. Ex: Clams and oysters
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Cephalopods
 Soft-bodied;
head is attached to a single foot. The
foot is divided into tentacles or arms. Ex: Octopus
and squids
Figure 27–23 The Anatomy of a Clam
Section 27-4
Stomach
Coelom
Shell
Heart
Nephridium
Adductor muscle
Mouth
Anus
Excurrent
siphon
Adductor
muscle
Incurrent
siphon
Gills
Mantle cavity
Intestine
Mantle cavity
Foot
End of class assignment
Draw a snail, a squid, and a clam.
(Figure 27-21- page 702)
 Label the foot, mantle, shell, radula, and
gills.
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Just Slinking or Wriggling in the Rain
Section 27-3
Have you ever noticed that after a spring rain,
earthworms come out of the soil and appear on
driveways, in puddles, and on sidewalks? Why does
this happen?
 1. An earthworm breathes through its skin. If its skin
dries out, it cannot breathe. Why would an earthworm
be more likely to “surface” during the rain than at
other times?
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The rain keeps the skin of the earthworm moist.
At other times, the earthworm is likely to dry out
and suffocate.
2. What types of weather conditions might be fatal
for an earthworm?
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Hot and dry weather is fatal for an earthworm
because its skin dries
out quickly.