Phylum%20Nematoda

1
Phylum Nematoda

• AKA Unsegmented roundworms.

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Nematodes

• Advancements over flatworms
• Has a two-hole digestive tract.
• Not as advanced as higher worms, such as
  earthworms because
• They lack body segmentation.

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Nematodes, contd

• Unsegmented roundworms are classified into about
  16,000 species, but the actual number of nematode
  species could be as high as 500,000.
• Nematode facts
• Colorless
• Range in length from microscopic to several
  meters long.
• May be free-living or parasitic.

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Nematode Habitat

• Nematodes live in
• Parasitic nematodes live within a host
• Free-living nematodes live in marine, freshwater,
  or damp soil environments.

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The Nematode lifestyles

• Nematodes generally live one of two types of
  lifestyles free-living or parastic.

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Free-living Lifestyle

• Eating habits
• Herbivores eat plants
• Carnivores eat animals
• Omnivores eat both plants animals
• Saprophagous -Eat dead organic matter (from
  animals only), Yummy
• Free-living and have the eating habits mentioned
  on the previous slide.
• The free-living nematodes are important because
  they add organic matter to the soil and putting
  holes in the soil to better allow water movement
  through the soil.

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Parasitic Lifestyle

• Parasitic feed off of a host.
• These worms feed of the blood or tissue fluids of
  their hosts.
• We will learn about four types of parastic
  nematodes filarial worms, hookworms, trichina
  worms, and ascaris worms.
• Interesting tidbits
• The filarial worms cause the disease
  elephantitis, pictured to the left.
• Trichina worms cause trichinosis the horrid
  disease contracted from eating undercooked pig
  products.

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Nematode Body Plan

• Nematodes have three cell layers
• Ectoderm outer tissue layer (epidermis)
• Mesoderm middle tissue layer (muscle)
• Endoderm innermost tissue layer (body cavity)
• They are known as psuedocoelomates because they
  have an internal cavity that is not lined with
  peritoneum therefore it is not a true coelom.
• They are bilaterally symmetrical as is every
  organism we study from here on out.

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Nematode Epidermis

• The outside of the nematode is made up of a
  tough, flexible, noncellular layer known as the
  cuticle.
• The cuticle is secreted by epidermal cells.
• It functions to
• Resist penetration in free-living.
• Resist enzymatic digestion in parasitic.
• Maintains internal hydrostatic pressure.
• The cuticle usually molts 4 times during
  maturation.

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Nematode Digestive System

• One way digestive system remember this means
  that food goes in one way and out another. Just
  like us.
• The digestive tract is a linear progression, as
  shown below
• mouth ? pharynx ? intestines ? rectum ? anus
• Food is pushed through this system by hydrostatic
  pressure.

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Nematode Musculature

• The nematode body wall has only longitudinal
  muscles.
• Remember longitudinal means lengthwise, so they
  only run from the anterior to the posterior end
  of the worm.
• These muscles are used for movement.
• When these muscles contract it causes the
  thrashing movements from head to tail.
• They lack circular muscles so they cannot crawl
  as we saw the leech do on dry surfaces.

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Excretory System

• Aquatic species have ventral glands (called
  renettes) posterior to the pharynx that absorb
  waste from the pseudocoelom and empties the waste
  through the excretory pore.
• Parasitic nematodes have a more advanced
  excretory system.

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Parasitic Excretory System

• Their system is known as a tubular system that
  develops from the renette system of the
  free-living worms.
• The renettes unite to form two large canals,
  known as the excretory canals that open to the
  outside by an excretory pore which is located by
  the head.
• A little odd to excrete wastes near your head,
  eh?

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Excretory System Diagram
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Reproductive System

• Most nematodes are
• Dioecious two different types of reproductive
  cells ex. sperm egg.
• Dimorphic two different sexes ex. male and
  female.
• As you might guess, they reproduce sexually.
• The males are slightly smaller than the females.
  Why?

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Female Reproductive System

• Consists of a pair of ovaries attached to an
  oviduct that has a swollen proximal end that
  forms a seminal receptacle.
• Each oviduct becomes a tubular uterus, and the
  two uteri come together to form a vagina that
  opens to the outside through a genital pore.

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Male Reproductive System

• Most male nematodes have only a single testis
  attached to the vas deferens which expands into a
  seminal vesicle which connects to the cloaca.
• What are all these things?
• Vas deferens aka sperm duct, releases sperm
• Seminal vesicle stores sperm cells
• Cloaca hole that sperm is ejected from
• They also have a flap of tissue called the bursa
  that aids in the transfer of sperm to the female
  genital pore.

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Reproductive System Diagram
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Brief Parasitic Nematode Info.

• Pinworms
• Most common roundworm in the U.S.
• Adults reside in the large intestine.
• Enter humans by being eaten.
• Hookworms
• Found in the southern U.S.
• Adults live in the small intestine of humans.
• Enter host through the skin, usually between the
  toes. That makes you want to walk around
  barefoot, doesnt it?
• Trichina
• Live in humans other omnivores (like piggys)
• Adults live in the small intestine of its host
  larvae encyst in the stomach and skeletal tissue
  (ouch!)
• Enter host by being eaten.

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Nematode Nervous System

• Nematodes have two nerve cords in their bodies.
• Ventral nerve cord runs along the belly.
• Dorsal nerve cord runs along the back.
• They have a central nervous system consisting of
  a circular brain.
• The nervous system allows the nematode to detect
  its environment and react to it.
• Aquatic nematodes have a pair of ocelli (eyes).