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Date & Time : 22, December 2024 17:51
General Characteristics of Annelida
Habitat
Annelids are mostly aquatic, marine or freshwater, but many are burrowing or free living.
Body organization
Triploblastic, bilaterally symmetrical metamerically segmented body.
First Phylum to possess a true coelom.
External Morphology
Elongated and vermiform.
Cuticle (secreted by epidermis) covers the whole body.
Locomotory organ - segmentally arranged setae or chaetae.
Appendages (if present) are unjointed. For example, parapodia in polychaetes.
Internal Anatomy
Respiration through body surface, in some by gills.
Blood vascular system - closed type. Blood is red due to the presence of haemoglobin.
Excretion by nephridia (paired and segmented).
Nervous system consist of brain and segmental ganglia.
Development
Direct development (when sexes are separate), indirect (when sexes are united).
Classification of Annelida
Phylum Annelida is classified into three classes:
1. Polychaeta
2. Oligochaeta
3. Hirudinea
Class Polychaeta
Class Oligochaeta
Class Hirudinea
A Few Examples
1. Pheretima
2. Chaetopterus
3. Aphrodite
4. Nereis
5. Heteronereis
6. Hirudinaria
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