Annelida

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PHYLUM ANNELIDA

GENERAL CHARACTERISTICS :
•Annelids are mostly aquatic, Marine or freshwater, burrowing or lining in tubes, some free living forms.
•Body triploblastic, symmetrical, elongated & vermiform.
•The body is metamerically segmented, externally by transverse grooves & internally by septa into a number of divisions, each division is called segment by metamere or somite.
•First segment is called peristomium which contains a part having mouth. This part is called prostomium. Last segment contains a part having anus called pygidium.
•The body wall consists of moist cuticle , it is single layered epidermis of columnar cells and well developed musculature , the cuticle is albuminoid .
•Body wall contractile, consists of an outer epidermis, Circular & longitudinal muscles.
•Appendages when present are unjointed.
•Locomotory organs are segmentally arranged, paired sitae or chaitae.
•Presence of three coelom divided by intersegmental septa.
•Alimentary canal is tube like extending straight from mouth to anus.
• Respiration through general body surface by gills , called as cutaneous .
•Blood vascular system is closed type. Blood is red due to presence of haemoglobin.
•Exterior by paired segmental nephridia which communicate the coelom to the exterior.
•Nervous system with a pair of cerebral ganglia (brain) and a double ventral nerve cord bearing ganglia and lateral nerves in each segment.



Classification of Annelida







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