Annelida: Definition, Characteristics, Examples

The phylum Annelida is a group of organisms having ring-shaped segments.

The term Annelida is derived from the Latin word;

” Annulus = ring “

There are more than 15000 known species of this phylum. This phylum includes several subgroups based on their identities and anatomical variations.

In 1802, Lamarck has first coined the term Annelida for the group of organisms belonging to the taxon vermis. Linnaeus introduced the taxon vermis for the group of worms in 1893.

Definition of Annelida

Phylum Annelida are the group of organisms having bilaterally symmetrical triploblastic metamerically segmented ring-like body containing true coelom, ventral nerve cord, and thin external cuticle.

Phylum Annelida

Characteristics of Annelida

Some common characteristic features of the phylum Annelida are:

  • The body is long cylindrical segmented ring-like.
  • Bilaterally symmetrical triploblastic body.
  • They have true coelom in their body.
  • The body is covered by thin cuticle layers.
  • Presence of a tubular and complete alimentary canal extending from mouth to anus.
  • In their body, the closed blood circulatory system is present.
  • The hemoglobin is present in the plasma, so the blood is red.
  • Presence of segmentally arranged setae as the locomotory organ.
  • Each segment of their body contains a pair of excretory organs called nephridia.
  • They have well-developed sense organs, and the nervous system is quite an advanced type.
  • Respiration occurs through the body wall.
  • The clitellum is present in all animals except the class Polychaeta.
  • Sexes may be separate, and some animals are hermaphrodites.
  • Trochophore larva is present in their life cycle.

Identification Characters

  • Body structure: The body is cylindrical and segmented into rings-like.
  • The coelom: In their body, the coelom is present.
  • Locomotory organ: The Setae is present as an excretory organ.
  • Excretory organ: The excretory organ nephridia is present in each part of the body.
  • Life cycle: In their life cycle, trochophore larva is found.


Some common animals of the Phylum Annelida are Pheretima(Earthworm), Nereis, Hirudinaria, Chaetopterus, Aphrodite, Serpula, Nerilla, Polygordius, Arenicola, etc.

Questions and Answers

1. The heart to pump blood evolved for the first time

a. Roundworms
b. Flatworms
c. Annelids
d. Arthropods

c. Annelids

2. Annelida larva is

a. Trochophore
b. Maggot
c. Tadpole
d. Bipinnaria

a. Trochophore

3. Clitellum is absent in

a. Eutypheus
b. Nereis
c. Pheretima
d. Hirudinaria

b. Nereis

4. Which of the following is not a characteristic feature of the phylum Annelida

a. Segmentation
b. Hydrostatic skeleton
c. Pseudocoelom
d. Close circulatory system

c. Pseudocoelom

Animesh Sahoo
Animesh Sahoo

Animesh Sahoo is a scientific blogger who is passionate about biology, nature, and living organisms. He enjoys sharing his knowledge through his writings. During his free time, Animesh likes to try new activities, go on adventures, experiment with different biological aspects, and learn about various organisms.

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