Phylum: Annelida

Screen Shot 2017-10-25 at 10.32.07 AM.png

“Earthworm” by flickr under CC by 2.0

Characteristics:

  • Coelomate, triploblastic
  • Protostome
  • Cephalization
  • Bodies are segmented, worm shape
  • Setae (chaetae)
  • Closed circulatory system
  • Metanephridia
  • Complete digestive system
  • Marine, freshwater, terrestrial

Different Classes:

Polychaeta (nearly all marine)

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“Polychaeta by Wikimedia Commons under CC by 2.0

-Lots of surface area, for gas exchange

-Highly vascular

Clitellata

  • Sublass Oligochaeta (terrestrial or freshwater)
  • Subclass Hirudinea

Metamerism- segmentation

  • Septa (peritoneum) divide the coelom into compartments, creates the segments
  • Each segments have repeated systems
  • Hydrostatic skeleton is partitioned
  • Circular musculature and longitudinal musculature
  • Closed Circulatory system- anterior blood vessels
  • Complete Digestive Tract- pharynx, brain, mouth, esophagus, hearts, crop, gizzard, excretory tubules, intestine, excretory pores, anus

-Earthworms play an essential role in aeratine soil and in adding nutrients

-Deposit Feeders

Metanephridia(tube open at both ends)- Nephtostome (entrance), Nephridiopore (exit)

Oligochaete Internal Anatomy

-Oligochaetes have no specialized respiratory structures

-Sexual Reproduction in Oligochaetes (simultaneous hermaphrodites)

Screen Shot 2017-10-25 at 10.29.25 AM.png

“Earthworm Dissection” by Wikimedia Commons under CC by 2.0

Subclass Hirudinea

  • No setae or appendages
  • Anterior and posterior suckers
  • Few body segments 33-34 more flattened dorsoventrally
  • No internal septa
  • Many are Ectoparasites

-Prostomium with tentacles, eyes, palps, cirri

-Many have an extendable proboscis with chitonous jaws/teeth

Sedentary Annelids- burrow or tube dwelling

Screen Shot 2017-10-25 at 10.40.25 AM.png

“Christmas Tree Worms” by Wikimedia Commons under CC by 2.0

Arenicola, a deposit feeder sedentary polychaeta which burrows in soft sediments

-Feather Duster

Regeneration and asexual reproduction in some polychaetes

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