Ch 13 Phylum Annelida

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Ch 13Phylum Annelida
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Phylum Annelida

• little ring
• Segmented worms
• 15,000 species
• Marine worms
• freshwater worms
• terrestrial worms
• Leeches
• worldwide distribution
• Soft body

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Size of Annelids

• lt1mm ? many meters

Megascolides australis up to 7.5 m!
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Fig. 9.9
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Fig. 9.9
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Characteristics of Phylum Annelida

• triploblastic
• schizocoelomate

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Fig. 9-13, p188
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Characteristics of Phylum Annelida

• Coelom partitioned by walls (septa)
• Serial (repeating) segmentation metamerism
• Each segment metamere/ somite

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Development of Metameric, Coelomic Spaces
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Characteristics of Phylum Annelida

• External evidence of septa circular grooves
  called annuli (rings)

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• Advantages of metamerism
• greater flexibility of movement Movie, compare to
  nematode
• Components organ systems repeated w/i segments
• (repeated excretory, nervous, circulatory
  structures)
• Built-in redundancy- increases survival

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• Note
• Not all organ systems are metameric
• ie, digestive system extends the length of the
  organism and is differentiated along its length

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Characteristics of Phylum Annelida

• Greater flexibility demands greater fine motor
  skills
• Highly developed, centralized nervous system
• brain
• Ventral nerve cord
• Ganglion in each metamere

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Movement in Phylum Annelida

• Fluid-filled coelom (except Subclass Hirudinea)
  hydrostatic skeleton
• Longitudinal and circular muscles

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Characteristics of Phylum Annelida

• Closed circulatory system (except some leeches)
• Blood vessels and aortic arches (hearts)
• Branch to every metamere

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Excretory System of Annelids

• Consists of paired metanephridia (in most)
• Excretory tubes with ciliated funnels that
  remove waste from the coelomic fluid
• open to the outside via excretory pores.

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Phylum Annelida Classes

• Class Polychaeta
• Class Clitellata
• Sublass Oligochaeta
• Subclass Hirudinea

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Class Polychaeta

• poly many chaeta bristles
• Mostly marine
• Example Neries)
• Mostly dioecious

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Class Polychaeta (contd)

• Parapodia
• fleshy segmented appendages for locomotion
  breathing
• have numerous setae at ends of parapodia

Fireworm (Hermodice carunculata)
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Class Polychaeta (contd)

• Gas exchange across parapodia

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Class Polychaeta (contd)

• parapodia have numerous setae at ends
• Tiny chitinous bristles
• Chitin tough, flexible polysaccharide not
  soluble in water
• Provide anchorage
• Swimming

Fireworm (Hermodice carunculata)
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Class Polychaeta (contd)

• well differentiated head (prostomium) with
  specialized organs (eyes, jaws)

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Class Polychaeta (contd)

• Many are euryhaline (able to tolerate a wide
  range of salinity conditions).
• Live under rocks, coral crevices, abandoned
  shells.
• Serve as the basis for many marine food chains.

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Class Clitellata

• Earthworms and leeches
• Few/no setae
• Possess clitellum

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Class Clitellata (contd)

• Clitellum
• secretes mucus for cocoon, copulation

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Class Clitellata (contd)

• monoecious, cross-fertilization

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Subclass Oligochaeta

• oligo few chaeta bristles
• Terrestrial, freshwater, some marine
• Example earthworms, night crawlers

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Subclass Oligochaeta (contd)

• Prostomium lacks sensory structures
• Parapodia are absent

bioweb.uwlax.edu/.../ earthworm_model_1a.htm
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Subclass Oligochaeta (contd)

• Feeds on organic or vegetable matter in soil
• May be as many as 50,000/acre
• Earthworms very beneficial in aerating the soil.
• capable of recycling up to 18 tons of soil/acre
  annually

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Do these questions now

1. The coelomic cavity of annelids is usually
   divided by walls called ________
2. What is metamerism?
3. What are the advantages of metamerism?
4. Is any part of the annelid not metameric? What
   part?
5. To what class do earthworms and leeches belong?

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Subclass Oligochaeta (contd)

• Gas exchange across moist skin ? to circulatory
  system

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Subclass Hirudinea

• Leeches
• Mostly freshwater
• possess clitellum apparent only during
  reproduction
• have annelid characteristics but generally lack
  setae
• Monoecious, cross-fert.
• Generally dorsoventrally flattened

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Subclass Hirudinea (contd)

• Predatory
• Attach to host via 2 suckers

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Subclass Hirudinea (contd)

• Locomotion
• More complex muscle system- includes oblique
  dorsoventral muscles
• inchworm movement via suckers movie

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Subclass Hirudinea (contd)

• Have a fixed number of metameres
• Internal septa are lacking
• coelom functions as a single, large chamber with
  connective tissue, muscle, and spaces

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Subclass Hirudinea (contd)

• Gas exchange across skin (in most)

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• squeamish?

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Medicinal leech

• Attach via suckers, pierce skin with sharp
  proboscis.
• Proboscis resembles 3 circular saw blades.
• Salivary glands secrete local anesthetic and an
  anti-coagulant.
• remove hematomas resulting from surgery

Ch 14