PHYLUM ANNELIDA
(NOTE: Classification with reference to Ruppert and
Barnes 6th 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
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.
·
· Eg- Hirudo sp, Dina sp, Acanthobdella sp,
Panthobdella sp, Hirudinaria sp
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Hirudinaria |
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Hope it helped you..... :)