Earthworm Anatomy

Body wall

  • The body wall of earthworm has an external covering of a thin, flexible cuticle.
  • The cuticle has many perforations, though which epidermal glands release their secretions.
  • The epidermis consists of
    • Columnar cells (supporting cells)
    • Glandular cells (which secrete mucus)
    • Sensory or receptacle cells (receives various types of stimuli)
    • Basal cells (present between columnar cells)
  • Setal sacs are also present in the epidermis.
  • There are two layers of muscles beneath the epidermal layer.
  • The outer layer is composed of circular muscles.
  • The inner layer is made of longitudinal muscles.
  • The innermost layer of body wall is the coelomic epithelium.

Digestive system

  • The digestive system is complete with mouth and an anal opening.
  • Thus, the body plan is tube-within-tube plan.
  • The mouth opens into the buccal cavity (segments 1 and 2).

  • The buccal cavity leads into a thick muscular pharynx which occupies the 3rd and 4th segments. It is surrounded by pharyngeal glands.
  • The pharynx follows a small narrow tube called oesophagus (5-7 segments), which continues into a muscular gizzard (8-9 segments).
  • Gizzard helps in grinding the food which is mostly soil particles, decaying leaves and other organic matter.
  • The stomach extends from 9-14 segments.
  • Stomach contains calciferous glands, which can neutralise the humic acid present in humus.
  • Intestine extends from 14nth segment to last segment.
  • In the 26th segment, a pair of short and conical intestinal caecae projects from the intestine.

  • The end parts of intestine possess several internal median folds of dorsal wall called typhlosole. This increases the effective area of absorption in the intestine.
  • The alimentary canal ends in a small rounded aperture called anus.


  • The excretory organs are coiled tubules called nephridia.
  • They are present in each segment (except 1 and 2).
  • There are 3 types of nephridia:

    • Pharyngeal nephridia:  They are found in pairs in the fourth fifth and sixth segments.
    • Integumentary nephridia: These are found attached to the inner surface of the body wall from the third segment the last segment.
    • Septal nephridia: These are found from segment 15 to the last segment. They open into the intestine.
  • Functions of nephridia: Regulation of volume and composition of the body fluids.
  • Structure of nephridia:

    • Initial part of nephridium is a funnel shaped structure called nephrostome. It collects excess fluids from the coelomic chamber.
    • The funnel leads to a tubular part called nephric tube which delivers the collected wastes into the digestive tube.
    • The wastes are expelled from the tubes through an external opening called nephridiopore.


Nervous system

  • The Nervous system in earthworm consists of
  • A cerebral ganglion (circumpharyngeal nerve ring)
  • A double ventral nerve cord (extending  from the fourth segment to the last segment)

  • The nerve cord bears segmental ganglia from which paired lateral nerves arise.
  • The nerve cord code in the anterior region (third and fourth segments) bifurcates, encircles the pharynx laterally enjoins the cerebral ganglia dorsally to form a nerve ring.


  • Earthworms don’t have specialised breathing devices.
  • Gas exchange occurs between the bloodstream and the moist body surface.


  • Blood vessels absorb the oxygen and carry it to the body parts.



Earthworm has closed type of blood vascular system or circulatory system. It consists of blood vessels, capillaries and a heart.

  • The blood is confined to the heart and blood vessels (since closed type of circulatory system is present).
  • Contractions of heart keep blood circulating in one direction.
  • Blood glands are present on the 4th 5th and 6th segments.
  • The blood glands produce blood cells and haemoglobin which is dissolved in the plasma.
  • Blood cells are usually phagocytic in nature.


Sensory system

  • The Sensory system in earthworm is composed of light, touch and chemoreceptors.
  • They do not have eyes. Instead, they have light receptor cells (photo receptors) which can distinguish lights of different intensity.

  • Receptor cells present in the epidermis (touch / epidermal receptors) helps to feel the vibrations on the ground.
  • They possess specialised chemoreceptors or taste receptors (buccal receptors) that respond to chemical stimuli.

  • All these sensory organs are present on the anterior part of the body.


  • Earthworms are called ‘friends of farmers’ because when they dig burrows in the soil, make the soil porous and soft.
  • This in turn health helps the plants penetrate deeper into the soil and also aids in their respiration.
  • In addition earthworms convert the dead organic matter in the soil into humus which increases the fertility of the soil.
  • Earthworms are commercially used in the production of vermicompost.  It is also one of the commonly used baits in fishing. 
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