Unit 4 - Phylums Platyhelminthes and Nematoda

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Unit 4 - Phylums Platyhelminthes and Nematoda

• Flatworms and Roundworms

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Phylum Platyhelminthes

• Largest group of acoelomate (no body cavity)
  worms
• Flatworms with middle tissue layer- mesoderm
• Tissues organized into organs
• Bilaterally symmetrical and flat
• Cells lie close to exterior enabling efficient
  diffusion of oxygen and carbon dioxide
• Highly branched gastrovascular cavity runs close
  to all tissues giving cells ready access to food
• No respiratory or circulatory systems

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Coelom Body Cavity

• The coelom usually performs multiple functions,
  including one or more of the following
• Provides room for organ development
• Surfaces for diffusion of gases, nutrients, and
  wastes
• Storage
• Hydrostatic support

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Phylum Platyhelmithes

• Flatworms
• Liver Flukes, Planaria and tapeworms
• Marine flatworms
• Characteristics
• Ribbon-like bodies
• Bilateral symmetry
• Branched digestive system
• No skeleton
• Asexual (fission) Hermaphrodites (sexual)
• Free movement
• Skin breathing

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Phylum Platyhelminthes

• Class Turbellaria
• Most free-living marine
• Dugesia- Freshwater planarians
• Digestion- Nutrients absorbed by intestinal wall
  and waste goes out through mouth
• Muscular pharynx comes out of central mouth to
  feed

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Phylum Platyhelminthes

• Reproduction- Mostly asexual by attaching
  posterior end to stationary object and pulling
  into two
• Hermaphrodites can reproduce sexually
• Nervous system Brain, two nerve cords, and
  light-sensitive eye spots
• Water balance- Water continually enters by
  osmosis
• Flame cells with cilia draw water to the outside

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Phylum Platyhelminthes

• Marine flatworm

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Phylum Platyhelminthes
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Planarian
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Phylum Platyhelminthes

• Many parasitic
• Endoparasite- internal
• Ectoparasite- external
• Class Cestoidea
• Subclass Eucestoda- Parasitic flatworms
  (tapeworms)
• Suckers and hooks on scolex (head) attach to
  walls of intestines and food absorbed from hosts
  intestines directly through the tapeworms skin

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Phylum Platyhelminthes

• String of rectangular body sections (proglottids)
• Each proglottid is a reproductive unit
• Added continually through life
• May grow up to 12 m (40 ft.) long

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Phylum Platyhelminthes

• Most occur in vertebrates
• Dozen types in humans
• Taenia saginata- Beef tapeworm
• Live in cow muscles in cysts
• High temp. kills larvae
• Subclass Cestodaria
• Body not subdidvided into proglottids
• Larvae in crustaceans adults in fish

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Scolex Examples
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Phylum Platyhelmithes
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Proglottid reproductive structure
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Phylum Platyhelminthes

• Largest flatworm class, Trematoda
• Parasitic worms called flukes
• Endoparasites or ectoparasites
• Subclass Aspidogastrea (Aspidobothrea)-
  Endoparasite of mollusks
• Subclass Digenea- Endoparasites of vertebrates

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Phylum Platyhelminthes

• Tegument- thick protective covering prevents them
  from being digested
• Take nourishment directly from hosts
• Use suckers to attach and the muscular pharynx to
  suck nourishment from hosts body fluids

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Phylum Platyhelminthes

• Complex life cycles involve more than one host
• Ex Schistosoma- Responsible for schistosomiasis
• From contaminated water
• Larvae bore into host skin into blood vessels of
  intestines
• Block vessels causing bleeding and damage to
  liver
• Snail is intermediate host

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Phylum Platyhelminthes

• Class Monogenea
• Monogenetic flukes
• One life cycle in one host
• Mostly ectoparasites on vertebrates

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Phylum Platyhelminthes

• Liver fluke

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Phylum Nematoda

• Roundworms- have a pseudocoelom (body cavity
  between endoderm mesoderm)
• Fluid movement serves as circulatory and gas
  exchange system
• Fluid also distributes nutrients to cells from
  digestive system

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Phylum Nematoda

• Long, cylindrical bodies
• Majority microscopic and free-living
• One-way digestive system
• Thick, flexible epidermis protects and gives
  shape
• Layer of muscle underneath pulls at epidermis and
  pseudocoelem for whip-like movement

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Phylum Nematoda

• Roundworms
• Ascaris, Trichinella and hookworms
• Characteristics
• Flattened bodies
• Bilateral symmetry
• Many are parasites
• Fluid-filled body cavity called a pseudocoelem
• Digestive tube
• No skeleton
• Sexual reproduction (Internal fertilization)
• Sperm is amoeboid
• Free movement
• Skin breathing

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Phylum Nematoda

• Class Secernentea (Phasmidea)- Phasmids (sensory
  structures) in tail
• Ascaris, Enterobius, Rhabditis, Turbutrix,
  Necator, and Wuchereria
• Class Adenophorea (Aphasmidia)- No phasmids
• Dioctophyme, Trichinella, Trichuris
• 50 species are parasitic
• Plant parasites feed on living plant cells in all
  parts of plant, causing wilting and withering
• 14 species affect humans
• Ex Enterobius (pinworms), Ascaris lumbricoides,
  Trichinella spiralis, Necator (hookworms)

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Phylum Nematoda

• Trichinella infects pigs and causes trichinosis
  (serious disease caused by eating undercooked
  pork)
• Necator live in warm, moist soils of the tropics
• Hookworm larvae enter bloodstream through soles
  of feet

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Phylum Nematoda

• Ascaris
• Carried in human waste
• After ingestion, eggs hatch into larvae in
  intestines
• Larvae bore through blood vessels, enter blood
  stream and then lungs (causes respiratory
  distress)
• Larvae may enter gallbladder or pancreas causing
  blockages
• Return to intestines to mature and mate
• May grow up to 1 ft. in length

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Phylum Nematoda

• Ascaris
• Trichinella

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Trichinosis

• Trichinella spiralis is found in pork
• Trichinosis is a disease caused by the
  Trichinella worm.
• Eggs hatch in the hosts gut
• Symptoms
• Diarrhea
• Fever
• Muscle pain
• Death

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Common Parasitic Roundworms

• Hookworms attach to the inside of the digestive
  tract
• Often found in pets

• Pinworms- most common
• Heartworms- transmitted to dogs by mosquitos
• Filarial worms- live in blood where they block
  blood vessels or lymph vessels causing severe
  swelling (Elephantitis)
• Guinea worm- Ingested with contaminated water
• Cause dracunculiasis
• Only found when exiting skin
• Found in Africa, India and Pakistan