Mollusks
Chapter 27
Facts and Fun
FlatwormsFlatworms
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 BANKNerve CordsPharynxGangliaDigestive CavityEyespot
FlatwormsFlatworms Form and function
Feeding Free living flatworms feed on tiny aquatic animals or they can
be scavengers and feed on recently dead animals
Respiration, 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 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.
MovementMove 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.
ReproductionReproduce 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
FlatwormsFlatworms
3 Groups of Flatworms3 Groups of Flatworms Turbellarians
Free living Live in marine or fresh water under stones, shells,
sand, or mud 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
RoundwormsRoundworms
Unsegmented worms that have psedocoeloms and digestive systems with two openings – a mouth and an anus.
RoundwormsRoundworms 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.
MovementMuscles that extend the length of their body
Aquatic – contract muscles to move like snakes Soil dwelling – push their way through soil by
thrashing around.
ReproductionReproduce sexually
Have separate sexes – either male or female Use internal fertilization
RoundwormsRoundworms
Pain and suffering in humansPain and suffering in humans 4 human disease4 human disease
1. Trichinosis causing worms Adult worm live and mate in the intestines of the
host including humans, pigs, and other mammals.
2. 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)
Pain and suffering in humansPain and suffering in humans3. Ascarid worms
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.
4. Hookworms 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?
How do the worms get back into the host (dogs)?
Through its fecesThrough its feces
Dog ingest the larva/egg or by eating the transport host
Eating undercooked meat containing larval cysts
Elephantiasis
HookwormsWorms attach to intestinal wall and suck blood, causing weakness and poor growth
AnnelidsAnnelids
Worms with segmented bodies Have a true coelom that is lined with tissue
derived from mesoderm.
AnnelidsAnnelids 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
Circulation Have a closed circulatory system – blood is
contained within a network of blood vessels
Movement Move 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.
AnnelidsAnnelids
Groups of AnnelidsGroups of Annelids Oligochaetes
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. Leeches
Parasites that suck blood and body fluids of their host. Can be used to treat medical conditions
Polychaetes 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.
Section 27-3
Anus
Clitellum
Circular muscle
Longitudinalmuscle
Nephridia Ganglia Ringvessels
Reproductiveorgans
Ventralblood vessel
Ganglion
Brain
Mouth
Dorsalblood vessel
CropGizzardBody segments
Setae
Figure 27–16 The Anatomy of an Figure 27–16 The Anatomy of an EarthwormEarthworm
MollusksMollusks Soft bodied animals that usually have an
internal and external shell. Include:
Snails Slugs Clams Squids Octopus
MollusksMollusks
Label:A.__________________
B.__________________
C.__________________
D. _________________
Have a larval stage called trochophore.
Soft bodies
MollusksMollusks
Form and function Body 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.
MollusksMollusks
Feeding Snails and slugs use a radula – tongue like structure to
which hundreds of tiny teeth are attached.
Respiration Aquatic – use gills to breathe Land dwelling – breathe using a mantle cavity that has a
large surface area lined with blood vessels.
Circulation 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
Movement Several 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.
RoundwormsRoundworms
Groups of Mollusks Gastropods
Shell less or single shelled that move by using a muscular foot located on the ventral side. Ex:Snail
Bivalves Two shells that are held together by one or two
powerful muscles. Ex: Clams and oysters
Cephalopods Soft-bodied; head is attached to a single foot. The
foot is divided into tentacles or arms. Ex: Octopus and squids
Section 27-4
Mouth
Shell
Stomach CoelomHeart
Nephridium
Adductor muscle
Anus
Excurrentsiphon
Incurrentsiphon
Gills
Mantle cavity
Foot
Intestine
Mantle cavity
Adductormuscle
Figure 27–23 The Anatomy of a ClamFigure 27–23 The Anatomy of a Clam
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.
Just Slinking or Wriggling in the Rain 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?Section 27-3
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? 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?
Hot and dry weather is fatal for an earthworm because its skin dries out quickly.