Digestive system of Earthworms

An earthworm is an invertebrate belonging to the phylum Annelida. They are found in the soil and make it fertile. They feed on dead organic matter. Pheritima and Lumbricus are the common earthworms found in India.

Earthworm is a hermaphrodite with a long, cylindrical and segmented body. The digestive system of earthworm comprises an alimentary canal that runs along the length of the body from mouth to anus and glands.

Table of Content:

• Characteristics of an Earthworm
• Structure of the Alimentary Canal
• Physiology of Digestion
• Frequently Asked Questions

Characteristics of an Earthworm

The main characteristic features of an earthworm are:

• Long, cylindrical and segmented body
• It is a hermaphrodite, having both male and female sex organs
• It has a hydrostatic skeleton
• It has a central and peripheral nervous system
• The setae present in the epidermal pits help in locomotion
• The epidermis is made up of columnar epithelial cells. It has secretory gland cells
• The digestive system runs along the body
• It respires through the skin
• It has a closed type of blood vascular system, which is made up of capillaries, vessels and a heart

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Digestive system of Earthworms

The digestive system of earthworm comprises an alimentary canal that runs along the length of the body from mouth to anus and glands.

Structure of the Alimentary Canal

The alimentary canal is long and straight and runs between the first and last segment of the body.

• Mouth: Mouth is the first segment called peristomium and is covered by prostomium, which acts as a wedge to force an open crack in the soil. The prostomium is sensory in nature. The mouth is a crescentic aperture which opens into the buccal cavity. Food ingestion takes place through mouth.
• Buccal Cavity: It extends from 2nd to 3rd segment. It is a thin-walled chamber. It can protrude out or retract in with the help of contraction of muscles attached to the body wall. It helps in holding the food during ingestion. Buccal cavity opens into a muscular chamber called the pharynx.
• Pharynx: It’s a thick-walled, pear-shaped chamber, which extends till 4th segment. It is differentiated from the buccal chamber by a dorsal groove where the brain of an earthworm is present. The dorsal part of the pharynx has a pharyngeal bulb, which is made up of muscle fibre, connective tissues, blood vessels and salivary glands. Salivary glands are unicellular and known as chromophil. Chromophil cells secrete saliva which contains proteolytic enzymes protease which converts protein to amino acids. Mucin is the other enzyme present, which makes the food soft. The pharyngeal wall is connected to the body wall through muscular strands which contract or dilate the pharyngeal lumen. It acts as a suction pump.

• Oesophagus: Pharynx continues into the oesophagus. It is a small narrow thin tube-like structure present on 5-7 segment. It passes food to the gizzard. It has no glands.
• Gizzard: It is present on 8-9 segment. It is a highly muscular thick-walled organ. It has an inner lining of the cuticle which makes it the hardest part of the alimentary canal. It helps in the grinding of soil particles and decaying leaves.
• Stomach: The stomach extends from 9-14 segments. It is a highly vascular and tubular structure. Three pairs of Calciferous glands are present in the segment 10-12, which produces carbonate of lime and helps in neutralising humic acid present in the humus. Glandular cells of the stomach secrete proteolytic enzymes which help in digestion of proteins. Stomach leads to the intestine.
• Intestine: It is a long thin-walled tube present from the 15^th segment till anus i.e. the last segment. The inner lining of the intestine is ciliated, vascular and glandular. The inner lining is folded to form villi. These villi increase the effective area of absorption in the intestine. The intestine is divided into 3 parts:
  • Pre-typhlosolar region: present from 15-26 segment. It contains villi. There is a short conical projection on the 26^th segment, which is known as intestinal caeca. Intestinal caeca extend upwards till 23^rd segment and secrete amylase enzyme. Amylase helps in the digestion of carbohydrates.
  • Typhlosolar region: Typhlosole is the large internal median fold of the dorsal wall of the intestine forming a longitudinal ridge, which is present after the 26^th segment, except the last 23^rd-25^th segments. Typhlosole increase the area of absorption in the intestine
  • Post-typhlosolar region: It’s the last 25 segments of intestine and also known as rectum. Intestinal villi and typhlosole are absent in this region. It stores faecal pallets and leads to the anus.
• Anus: It is a small round aperture present in the last segment. The alimentary canal of an earthworm opens to the exterior through the anus. Undigested food is excreted out through the anal opening in the form of worm casting.

Physiology of Digestion

Earthworm feeds on dead and decaying organic matter present in the soil. This material is gathered at night. The digestion of earthworm is an extracellular process.

The enzyme present in the intestine are:

• Protease: Protein to amino acids
• Amylase: Starch to glucose
• Lipase: Fats to fatty acid and glycerol
• Cellulase: Cellulose to glucose
• Chitinase: hydrolyse glycosidic bonds in chitin

Learn more about structural organisation in animals only at BYJU’S.

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