Phylum Annelida

+General Annelid Characteristics 

• Coelomate, Triploblastic
• Protostome (lophotrochozoan)
• Cephalization
• Bodies are segmented, worm-shaped
• Setae (chaetae)
• Closed circulatory system
• Metanephridia
• Complete digestive system
• Marine, freshwater, terrestrial

+Class Polychaeta (nearly all marine)

+ Parapodia function in locomotion and gas exchange, are highly vascularized and increase the surface area of the body wall. (Many Setae)

Class Clitellata

– Subclass Oligochaeta (mostly terrestrial or freshwater)

                                                              Anatomy of an Earthworm 

+ They have a closed circulatory System, complete digestive Tract and exhibit cephalization.

+ Earthworms play an essential role in aerating the soil and in adding nutrients.

+ They are Metanephridia so they have a tube open at both ends.

+ Oligochaetes have no specialized respiratory structures. (simultaneous hermaphrodites)

Subclass Hirudinea (mostly freshwater, terrestrial)

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

+ Many have an extendable proboscis with chitinous jaws/teeth.

+ Arenicola, a deposit feeder, sedentary polychaete which burrows in soft sediments.

+ Feather Duster Worm is a marine polychaete.

+ Regeneration and asexual reproduction in some Polychaetes