Annelida

Subject: Biology

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Overview

Annelida is composed of two words i.e. annulus which means ring and eidos which means form. This note contain information which include general characteristic features, classification of phylum Annelida.
Annelida
Example of phylum Annelida
source:www.kullabs.com
fig:Example of phylum Annelida

Annelida is composed of two words i.e. annulus which means ring and eidos which means form. Lamarck coined the term Annelida.

General characteristic features of phylum Annelida:

  • They are elongated and metamerically segmented.
  • They are mostly aquatic and some are terrestrial and burrowing. Few are ectoparasites sucking the blood from vertebrates.
  • They are triploblastic.
  • They are bilaterally symmetrical.
  • It is true coelom type formed by mesoderm. Such coelom is called schizocoelous.
  • It takes place by setae or parapodia or suckers.
  • Nutrition is a holozoic type.
  • The alimentary canal is straight and well developed. Digestion is entirely extracellular.
  • Respiration takes place through a moist body surface by diffusion.
  • Blood vascular system is closed type consisting of hearts and blood vessels.
  • Excretion takes place through segmentally arranged nephridia.
  • The body contains metameric segmentation.
  • Presence of distinct head. The nervous system consists of a pair of cerebral ganglia and double solid ventral nerve cord.
  • Reproduction is usually hermaphrodite. Some cases, there is unisexual. Fertilization is cross and internal.
  • Development may be direct or indirect with the larval stage as trochophore.

Classification:

Annelida is classified into four classes on the basis of locomotory organs.

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Amphitrite
source:www.luckyshow.org
fig:Amphitrite

Polychaeta:

  • Locomotory organs are parapodia.
  • Mainly marine, some freshwater.
  • Clitellum is absent.
  • Sexes are separate.
  • Fertilization is external. Development is indirect.
  • Example: Nereis, Amphitrite

Oligochaeta:

  • Locomotory organs are setae found in each segment.
  • Mostly terrestrial, some fresh water.
  • Clitellum is present.
  • They are hermaphrodite.
  • Fertilization is external, occurs in a cocoon.
  • Development is direct.
  • Example: Pheretima, Negascolen.

Hirudo
source:www.uniprot.org
fig:Hirudo

Hirudinea:

  • Locomotory organs are suckers.
  • Mostly freshwater and terrestrial, some marine.
  • They are mostly ecoparasites having suckers.
  • Clitellum is only seen during a breeding season.
  • Fertilization is external, occurs in a cocoon.
  • Example: Hirudinaria, Hirudo.

Arachiannelid:

  • Segmentation is internal only.
  • Exclusively marine.
  • Parapodia and setae are present.
  • Tentacles are present.
  • Sexes are separate. Development is indirect.
  • Example: Polygordius, Protgdrillus.

Things to remember
  •  Lamarck coined the term Annelida.
  • They are elongated and metamerically segmented.
  • They are mostly aquatic and some are terrestrial and burrowing.Few are ectoparasites sucking the blood from vertebrates.
  • Respiration takes place through a moist body surface by diffusion.
  • Blood vascular system is closed type consisting of hearts and blood vessels.
  • Annelida is classified into four classes on the basis of locomotory organs.

 

  • It includes every relationship which established among the people.
  • There can be more than one community in a society. Community smaller than society.
  • It is a network of social relationships which cannot see or touched.
  • common interests and common objectives are not necessary for society.

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