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.