Phylum Annelida Animals, Animals Classification, Zoology Help

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Phylum Annelida Animals

This is eucoelomate or the coelomate phylum possess a true coelom or secondary body cavity. This coelom is bounded by the mesothelium.

Definition: These are metamerically segmented, bilaterally symmetrical, true coelomate animals. Typically all annelids are provided with chitinous setae which are embedded in the pits of the skin.

Phylum Annelida Animals General Characters:

1. Truely segmented worm's body is externally as well internally divided by a number of rings or annulii.

2. Organ system grade body organisation in which organs form the system.

3. Symmetry: Triploblastic, bilaterally symmetrical, coelomate.

4. Locomotion: By chitinous setae or muscular para podia.

5. Digestive system: Well developed and extracellular digestion.

6. Blood circulatory system: Closed type. Respiratory pigment dissolved in plasma.

7. Respiration: By humid skin or parapodia or cephalic gills.

8. Excretory system: Segmentally arranged nephridia.

9. Nervous system: One pair of cerebral ganglia (or brain) and a double nerve cord with a pair of ganglia in each segment.

10. Sense organs: Organ of touch, taste buds, statocyst, photosensitive cells and eye with lens.

11. Sex: Hermaphrodite or unisexual.

12. Development: Spiral cleavage and determinate type. If development is indirect then the name of larva is trochophore.

13. Habit and habitat: Mostly aquatic, marine and fresh water. Some are terrestrial burrowings animal, some are symbiont and some are parasite.


Class 1-Polychaeta e.g. aphrodite, nereis, chaetopterus, arenicola, sabella.

Class 2-Oligochaeta e.g. tubifex, lumbricus, pheretima, megascolex.

Class 3-Hirudinea e.g. glossiphonia, hirudo, hirudinaria.

Class 4-Archiannelida e.g. polygordius, protodrillus.

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