Classification of Annelida

                    PHYLUM ANNELIDA

(NOTE: Classification with reference to Ruppert and Barnes 6^th edition 1994)

Diagnostic Features:

•        Body Triploblastic, Vermiform and Bilaterally Symmetrical. They possess Metamerism.  

•       Closed Circulatory system present.
•    Digestive system complete, comprises of a muscular gut with mouth and anus.
•   Excretory system with pairs of Nephridia arranged in each metamere.
•   Sexes separate or hermaphrodite, Development via Free swimming Trocophore larvae.

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Classification: 

                                  Phylum Annelida

·       Class Polychaeta

·       Class Oligochaeta

·       Class Hirudinea

Class Polychaeta

•    Predominantly Marine, with Errant type and sedentary type. Errant type    can do burrowing, swimming, crawling and tube dwelling. But sedentary type can do burrowing and tube dwelling only.
•    Head distinct, bearing head, tentacle, sirri and palps.
•   Pharynx with teeth or jaws (in errant type), Pharynx without teeth (in sedentary type).  
•    They have great power of regeneration, they can regenerate any part of the body including tentacle and even head.
•       Mostly Dioceous but some are hermaphrodite. Gonads escape by the rupturing of the body or through nephridia.
•     Development indirect via trocophore larvae that undergo metamorphosis.

·                                                    Eg- Nereis sp, Aphrodite sp, Sebella sp, Cheatopterus sp

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Nereis

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Class Oligochaeta

•   Mostly terrestrial, but some are fresh water forms.
•   Head indistinct, Prostomium either small rounded lobe or cone, appendages absent.
• Body segments without parapodia, instead setal sacs are present which assists in locomotion
•   Asexual reproduction by spontaneous fission (Schizogenesis).
•  Development direct without larval stage.

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Eg- Tubifex sp, Megascolex sp, Pheretima sp, Lumbricus sp, Metaphire sp

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Class Hirudinea

•  Habitat- marine, fresh water and terrestrial forms.
•  Body dorsoventrally flattened body with fixed 33 segments.
•     Body with 2 suckers- (1) Posterior large powerful sucker and (2) Anterior small sucker.
• Absence of Setae, Parapodia and tentacle.
• Hermaphrodite, several pairs of testis present, one pair of ovary present and one genital opening. 
•      Development direct without larval stage. 

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·    Eg- Hirudo sp, Dina sp, Acanthobdella sp, Panthobdella sp, Hirudinaria sp

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Hirudinaria

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 Hope it helped you..... :)