Phylum Annelida

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• Phylum Annelida

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Introduction
(Example of Convergent Evolution)

• Annelids (segmented worms) are extremely
  successful and have invaded terrestrial,
  freshwater, and marine habitats.
• They include familiar forms such as earthworms
  and leeches and many diverse marine organisms.
• The segmentation characteristic of this phylum
  extends to the interior of the animal and is more
  complex than the annulations of the rotifera and
  nematodes.
• Metamerism, a repetition of similar body parts,
  is related to the segmentation and is probably an
  adaptation for locomotion.

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Introduction

• There are three major classes you need to be
  familiar with
• 1) Polychaeta
• 2) Hirudinea
• 3) Oligochaeta

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Class Polychaeta

• Polychaetes are the most structurally diverse of
  the annelids and are exclusively marine.
• Polychaetes have many setae (poly"many") and
  gill- or fin-like appendages called parapodia. In
  some species the setae may cover the entire body
  which gives it a furry appearance (sea mouse,
  Aphrodite).
• Others have hollow poison-tipped setae used for
  defense (as in the "fire worms"). The parapodia
  may be relatively simple (Nereis), or extremely
  complex and varying from segment to segment
  (Chaetopterus).
• Eyes, tentacles, palps, and pincer-like jaws are
  the rule. The heads of plume and feather duster
  worms are endowed with tentacles to capture prey.
  
• Polychaetes are mostly dioecious

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• And theyre colorful!

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Class Hirudinea

• This freshwater class of annelids is commonly
  called leeches.
• They usually have an anterior sucker surrounding
  the mouth and a ventrally-facing posterior
  sucker.
• They are monoecious, but asynchronously so
  (individuals switch between being male or female,
  but are never both at the same time).
• Although leeches have a reputation as being blood
  suckers, most are predacious.

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Class Oligochaeta

• Examples include earthworms and many freshwater
  forms.
• The head is degenerate with few obvious sensory
  structures (owing to their burrowing habits).
• Oligochaetes have few setae (spine-like
  appendages oligo"few", chaeta"setae").
• Members of this class also possess a reproductive
  structure called the clitellum (a reproductive
  structure).
• Oligochaetes are monoecious

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• Dissection Information

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Dissection
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Dissection