Department of Zoology at ANDC/Zoology Museum/Museum specimens/Annelida

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Phylum Annelida

Date & Time : 4, March 2024 21:56

General Characteristics of Annelida


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.


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