Phylum Annelida

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Phylum Annelida

• The Segmented Worms

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Classes of Annelida

• Class Polychaeta (fanworms, clam worms)
• Class Oligochaeta (earthworms)
• Class Hirudinea (Leeches)
• Classes not covered
• Class Branchiobdellida
• Class Acanthobdellida

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General Characteristics

• Annelids are to be found in marine, freshwater,
  and terrestrial habitats
• The body is vermiform, bilaterally symmetrical,
  and segmented
• Each segment is separated from contiguous ones by
  a transverse septum
• The body is triploblastic with a well developed
  coelom
• The body is covered with a flexible non-chitinous
  cuticle

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General Characteristics

• Most forms have setae, hard, bristle-like
  chitinous structures
• Digestive system is complete
• Circulatory system is closed,
• Excretory system typically consists of a pair of
  nephridia per segment

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Typical Arrangement of Segments
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Class - Polychaeta

• Feather Duster worms, Clam worms, Christmas Tree
  worms

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General Characteristics

• Mostly marine and free-living
• Many setae, on fleshy lateral outgrowths of the
  body wall known as parapodia
• Well developed head bearing appendages
• Sexes separate, with a free-swimming trochophore
  larva

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Nereis
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Parapodium
Parapodia
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Figure 17.03d
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Some Polychaets
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Figure 17.co
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Figure 17.02a
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Figure 17.02b
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Figure 17.09
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Class Oligochaeta

• Earthworms and Freshwater Worms

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General Characteristics

• Are terrestrial with a few freshwater species
• Have few setae
• No parapodia
• No distinct head appendages
• Clitellum present
• Hermaphrodites, with copulation required
• Eggs are deposited in a cocoon and development is
  direct

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Figure 17.12a
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Earthworm Dissection
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Earthworm Dissection
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Figure 17.12c
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Figure 17.14
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Figure 17.15
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Figure 17.17
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Some Oligochaets
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Figure 17.18b
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Figure 17.18c
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Figure 17.18d
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Figure 17.17g
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Class Hirudinea
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General Characteristics

• Ectoparasites, not all - many feed on organic
  debris
• Usually dorso-ventrally flattened with fixed
  number of body segments (34)
• No setae or parapodia
• Clitellum present only during reproduction
• Two suckers anterior and posterior

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Figure 17.20
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