Worms and Mollusks

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Worms and Mollusks

• Chapter 27

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Flatworms

• Section 27-1

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What is a flatworm?

• Phylum Platyhelminthes
• No more than a few millimeters thick
• Have tissues and internal organ systems
• Have bilateral symmetry and cephalization
• Known as acoelomates (without coelem, which is
  a fluid filled body cavity)

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Form and Function in Flatworms

• Feeding
• Digestive cavity with a single opening through
  which both food and wastes pass
• Parasitic worms obtain nutrients from foods that
  have already been digested by their hosts

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Form and Function in Flatworms

• Respiration, Circulation, and Excretion
• Rely on diffusion to
• Transport oxygen and nutrients to internal
  tissues
• Remove carbon dioxide and other wastes from their
  bodies
• Have no gills or respiratory organs, heart, blood
  vessels, or blood
• Some have flame cells remove excess water and
  filter wastes from the body

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Excretory System
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Form and Function in Flatworms

• Response
• A head encloses several ganglia (groups of nerve
  cells) that control the nervous system
• Have eyespots that look like eyes, but are groups
  of cells that can detect changes in the amount of
  light in their environment

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Form and Function in Flatworms

• Movement
• Two means of movement
• Cilia to help glide through water
• Muscle cells allow them to twist and turn

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Form and Function in Flatworms

• Reproduction
• Most are hermaphrodites that reproduce sexually
• A hermaphrodite is an individual that has both
  male and female reproductive organs
• Asexual reproduction takes place by fission, in
  which an organism splits in two

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Groups of Flatworms

• Three main groups of Flatworms
• Turbellarians
• Flukes
• Tapeworms
• Most turbellarians are free-living
• Most other flatworm species are parasites

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Turbellarians

• Free-living flatworms
• Live in marine or freshwater

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Flukes

• Class Trematoda
• Parasitic flatworms
• Infect the internal organs of their host

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Tapeworms

• Class Cestoda
• Long, flat, parasitic worms
• Adapted to life inside the intestines of their
  host
• No digestive tract
• Absorb already digested nutrients from host

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Roundworms

• Section 2

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What is a Roundworm?

• Phylum Nematoda
• Slender, unsegmented worms with tapering ends
• Range in size from microscopic to a meter
• Most are free-living, inhabiting soil and water
• Others are parasitic

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What is a Roundworm?

• Have a pseudocoelom (false coelom)
• Have a digestive tract with two openings a
  mouth and an anus

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Form and Function in Roundworms

• Have specialized tissues and organ systems
• Body systems of free-living roundworms are more
  complex than parasitic ones

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Form and Function in Roundworms

• Feeding
• Predators that use grasping mouthparts to catch
  and eat small animals
• Respiration, Circulation, and Excretion
• Exchange gases and excrete metabolic waste
  through their body walls
• Depend on diffusion to carry nutrients and waste
  through their bodies

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Form and Function in Roundworms

• Response
• Simple nervous systems
• Have several types of sense organs
• Movement
• Muscles extend the length of their bodies
• Reproduction
• Reproduce sexually, and most have separate sexes

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Roundworms and Human Disease

• Parasitic roundworms include
• Trichinosis-causing worms
• Filarial worms
• Ascarid worms
• Hookworms

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Trichinosis-Causing Worms

• Trichinosis terrible disease caused by the
  roundworm Trichinella
• Adult worms live and mate in the intestines of
  their hosts
• Humans usually get the disease from eating
  undercooked pork

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Filarial Worms

• Threadlike worms that live in blood of birds and
  mammals
• Causes elephantiasis

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Ascarid Worms

• Serious parasite of vertebrate animals
• Causes malnutrition in more than 1 billion people
  worldwide
• Absorbs digested food from the hosts small
  intestine

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Hookworms

• 25 of people in the world are affected with
  hookworms
• Live in hosts intestines
• Feed on blood, causing weakness and poor growth

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Annelids

• Section 27-3

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What is an Annelid?

• Phylum Annelida
• Worms with segmented bodies
• Each segment is separated by a septum
• Have a true coelom

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Form and Function in Annelids

• Feeding and Digestion
• Many get their food using a pharynx
• Food moves from the pharynx, into the esophagus,
  the crop, the gizzard, and then to the intestine
• Others obtain food by filter feeding
• Circulation
• Closed circulatory system blood is contained
  within a network of blood vessels

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Form and Function in Annelids

• Respiration
• Aquatic annelids often breath through gills
• Land-dwelling annelids take in oxygen and give
  off carbon dioxide through their moist skin
• Excretion
• Digestive wastes pass through the anus at the end
  of the digestive tract
• Cellular waste is eliminated through nephridia
  (excretory organs)

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Form and Function in Annelids
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Form and Function in Annelids

• Response
• Well developed nervous system consisting of a
  brain and several nerve cords

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Form and Function in Annelids

• Movement
• Two groups of muscles that work together as part
  of a hydrostatic skeleton
• Reproduction
• Most reproduce sexually
• Some have separate sexes, others are
  hermaphrodites

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Groups of Annelids

• Three classes of Annelids
• Oligochaetes
• Leeches
• Polychaetes

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Oligochaetes

• Class Oligochaeta
• Contains earthworms and their relatives
• Streamlined bodies
• Relatively few setae
• Most live in soil or freshwater

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Leeches

• Class Hirudinea
• External parasites that suck the blood and body
  fluids of their host

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Polychaetes

• Class Polychaeta
• Contains sandworms, blood worms, and relatives
• Marine annelids that have paired, paddlelike
  appendages tipped with setae (brushlike
  structures)

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Ecology of Annelids

• Earthworms and many other annelids spend their
  lives burrowing through soil, aerating and mixing
  it
• Earthworms help plant matter decompose
• Earthworm castings are rich in nitrogen,
  phosphorus, potassium, micronutrients, and
  beneficial bacteria

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Mollusks

• Section 4

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What is a Mollusk?

• Soft-bodied animals
• Usually have an internal or external shell
• Free-swimming larval stage called a trocophore

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Form and Function in Mollusks

• True coeloms
• Complex, interrelated organ systems

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Form and Function in Mollusks

• Body Plan
• Variation on four main parts
• Foot takes many forms
• Mantle layer of tissue that covers the
• mollusks body
• Shell made by glands in the mantle
• Visceral mass consists of internal organs

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Form and Function in Mollusks

• Feeding
• Can be herbivores, carnivores, filter feeders,
  detritivores, or parasites
• Snails and slugs feed using a tongue-shaped
  structure called a radula

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Form and Function in Mollusks

• Feeding
• Clams, oysters, and scallops use gills
• Food enters through a siphon tubelike structure
  through which water enters and leaves the body

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Form and Function in Mollusks

• Respiration
• Aquatic mollusks breathe using gills inside their
  mantle cavity
• Land snails and slugs respire through the moist
  surface of their skin

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Form and Function in Mollusks

• Circulation
• Some have open circulatory systems works well
  for slow-moving mollusks (snails and clams)
• Others have closed circulatory systems works
  best for fast moving mollusks (octopi and squid)

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Form and Function in Mollusks

• Excretion
• Nephridia remove wastes from the blood and
  release it outside the body

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Form and Function in Mollusks

• Response
• Two-shelled mollusks have simple nervous systems
• Octopi and relatives have the most highly
  developed nervous systems of all invertebrates
• Octopus opening a jar

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Form and Function in Mollusks

• Movement
• Move in a variety of ways
• Snails secrete mucus and move over surfaces using
  the foot
• Octopi use a form a jet propulsion

• Reproduction
• Reproduce in a variety of ways
• Snails and two-shelled mollusks external
  fertilization (sexually)
• Tentacled mollusks and some snails internal
  fertilization (sexually)

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Groups of Mollusks

• Three major classes
• Gastropods
• Bivalves
• Cephalopods

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Gastropods

• Class Gastropoda
• Shell-less or single-shelled
• Move using muscular foot on ventral side
• Includes pond snails, land slugs, sea
  butterflies, sea hares, limpets, and nudibranchs

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Bivalves

• Class Bivalvia
• Have two shells held together by one or two
  powerful muscles
• Include clams, oysters, mussels, and scallops

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Cephalopods

• Class Cephalopoda
• Soft-bodied
• Head is attached to a single foot
• Foot is divided into tentacles or arms
• Includes octopi, squids, cuttlefishes, and
  nautiluses

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Ecology of Mollusks

• Mollusks play many different roles in living
  systems
• Feed on plants
• Prey on animals
• Filter algae out of the water
• Eat detritus
• Some mollusks are hosts to symbiotic algae or to
  parasites others are themselves parasites
• Mollusks are food for many organisms