Phylum Annelida (little Rings)

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Phylum Annelida (little Rings)

• Segmented Worms

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Characteristics of Phylum Anneldia

• 1. Bilateral Symmetry
• 2. Metameric their bodies are divided into
  segments, both inside and out this allows for
  parts of the worm to be damaged or destroyed
  without killing the worm
• 3. Complete nervous, digestive, circulatory
  system
• 4. Triploblastic Coelomates
• Triploblasts have an ectoderm, endoderm, and
  mesoderm.
• Coelomates have a body cavity within the mesoderm
  for housing organs.
• 5. Covered in tiny hairs called chaetae

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Segmentation

• 1. Allows movement w/maximum protection.
• 2. Each segment contains its own set of excretory
  organs and muscles, separated from the next
  segment by a septum.

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3 Major Classes

• 1. Class Polychaeta (many hairs) marine
  annelids, usually very fancy and beautiful
• 2. Class Oligochaeta (few hairs) freshwater,
  marine, and terrestrial earthworms
• 3. Class Hirudinea - Mostly freshwater, some
  marine, some parasites leeches

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Class Polychaeta

• Largest of the annelid classes
• Dioecious
• Have parapodia, literally meaning pairs of feet
  for swimming and crawling.
• Have setae bristles that aid in movement and
  burrowing
• Have two to four pairs of eyes, but still see
  mostly just light and dark.
• Have a proboscis modified pharynx used for
  feeding. What other animals have a proboscis?
• Have an anus (like roundworms), but their waste
  has a special name castings.
• Blood may be either red, green, or colorless
  depending on the worm.
• Can regenerate lost parts.

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Class Oligochaeta

• Have a clitellum that secretes mucus during
  mating, and forms a cocoon for fertilized eggs.
  Since they are monoecious, they exchange sperm
  during copulation.
• Feed primarily on decaying vegetation using their
  pharynx
• Have very primitive eyes similar to that of
  flatworms.
• These guys are NOT regenerative like other worms.

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Class Hirudinea

• Monoecious
• Pharynx has evolved into a modified sucker, used
  for penetrating the outer layers of its prey and
  feeding on bodily fluids, i.e. blood.
• Not capable of regeneration!