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earthworm

Earthworm ( pheretima Earthworm ( pheretima posthuma )posthuma )

Phylum : AnnelidaPhylum : Annelida

Class : OligochoetaClass : Oligochoeta

Family : lumbricidaeFamily : lumbricidae

Genus : PheretimaGenus : Pheretima

Species : PosthumaSpecies : Posthuma

Earthworm Earthworm

Earthworm is a reddish brown terrestrial Earthworm is a reddish brown terrestrial invertebrate that inhabits the upper invertebrate that inhabits the upper layer of the moist soil.layer of the moist soil.

During day time, they live in burrows and During day time, they live in burrows and that is made of boring and swallowing that is made of boring and swallowing the soil.the soil.

There are about 500 species of pheretima There are about 500 species of pheretima found in India. found in India.

Earthworm have long cylindrical body. The Earthworm have long cylindrical body. The body is divided into more than hundred short body is divided into more than hundred short segments and they are similar to each other. segments and they are similar to each other. The dorsal surface of the body is marked by a The dorsal surface of the body is marked by a dark median mid dorsal linedark median mid dorsal line along the along the longitudinal axis of the body.longitudinal axis of the body.

Ventral surface is distinguish by the presence Ventral surface is distinguish by the presence of genital openings.of genital openings.

Anterior end consists of mouth and Anterior end consists of mouth and prostomium.prostomium.

MOUTH : A lob which serves as a covering for MOUTH : A lob which serves as a covering for the mouth and as a wedge to force open the mouth and as a wedge to force open cracks in the soil into which the earthworm cracks in the soil into which the earthworm may crawl.may crawl.

And the prostomium is sensory in functions.And the prostomium is sensory in functions.

The first body segment is called peristomium. The first body segment is called peristomium.

In mature worm, there are 14 – 16 In mature worm, there are 14 – 16 segments are covered by a prominent segments are covered by a prominent dark band of glandular tissue called dark band of glandular tissue called clitellumclitellum

Thus the body is divided into three Thus the body is divided into three prominent -:prominent -:

* Preclitellar* Preclitellar

* Clitellar * Clitellar

* Posticlitellar segments.* Posticlitellar segments.

Four pairs of spermathecal is suitated on Four pairs of spermathecal is suitated on ventro-lteral sides of the intersegmental ventro-lteral sides of the intersegmental grooves 5-9 segments.grooves 5-9 segments.

A single female genital is present in the A single female genital is present in the mid-ventral line of 14 segment.mid-ventral line of 14 segment.

And a pair of male genital pores are And a pair of male genital pores are present on the ventro-lateral sides of the present on the ventro-lateral sides of the 18 segments 18 segments

Numerous minute pores called Numerous minute pores called nephridispors open on the surface of the nephridispors open on the surface of the body.body.

In each body segment, except the In each body segment, except the first, last and clitellum, there are first, last and clitellum, there are rows of s-shaped setae, embedded rows of s-shaped setae, embedded in the epidermal pits in the middle in the epidermal pits in the middle of each segment.of each segment.

Setae can be extended or retracted. Setae can be extended or retracted.

Their principal role is in locomotion.Their principal role is in locomotion.

The body wall of the The body wall of the earthworm is covered by a earthworm is covered by a thin non-cellular cuticle, below thin non-cellular cuticle, below which is the epidermis and which is the epidermis and

Two muscle layers :-Two muscle layers :-

* Circular and longitudinal;* Circular and longitudinal;

And an intermost coelomic And an intermost coelomic epithelium. epithelium.

Epidermis is made by a single Epidermis is made by a single layer of columnar epithelial cells layer of columnar epithelial cells which contains secretory gland which contains secretory gland cells. cells.

Alimentary canal is a straight tube Alimentary canal is a straight tube it flows btw first to last segment it flows btw first to last segment of the body.of the body.

A terminal A terminal mouth mouth opens into opens into the buccal the buccal cavity (1-3 cavity (1-3 segments) segments) which which leads to leads to muscular muscular pharynxpharynx..

A small tube oesophagus (5-7 segments) A small tube oesophagus (5-7 segments) continues into muscular gizzard (8-9 continues into muscular gizzard (8-9 segments).segments).

It helps in grinding the soil particles and It helps in grinding the soil particles and decaying leaves.decaying leaves.

The stomach extends from 9-14 segments.The stomach extends from 9-14 segments.

The food of the earthworm is decaying The food of the earthworm is decaying leaves and organic matter mixed with leaves and organic matter mixed with soilsoil..

Calciferous glands, present in the Calciferous glands, present in the stomach, neutralise the humic stomach, neutralise the humic acid present in humus.acid present in humus.

Intestine starts from the 15 Intestine starts from the 15 segments onwards till the last segments onwards till the last segments.segments.

Pair of short and conic intestinal Pair of short and conic intestinal caecae project from the intestinal caecae project from the intestinal 26 segment.26 segment.

The characteristics feature of the The characteristics feature of the intestine between 26-segments is intestine between 26-segments is the presence of internal median fold the presence of internal median fold of dorsal wall called typhlosole.of dorsal wall called typhlosole.

This increase the area of absorption This increase the area of absorption in the intestine.in the intestine.

The alimentary canal opens to the The alimentary canal opens to the exterior by a small rounded aperture exterior by a small rounded aperture called anus.called anus.

The ingested organic rich soil The ingested organic rich soil passes through the digestive passes through the digestive tract where digestive enzymes tract where digestive enzymes breakdown complex food into breakdown complex food into smaller absorbable units.smaller absorbable units.

These simpler molecules are These simpler molecules are absorbed through intestinal absorbed through intestinal membrane and are utilised.membrane and are utilised.

Pheretima exhibits a closed Pheretima exhibits a closed type of blood vascular type of blood vascular system, consisting of blood system, consisting of blood vessels, capillaries and heart. vessels, capillaries and heart. Contraction keeps blood Contraction keeps blood circulating in one direction.circulating in one direction.

smaller blood vessels smaller blood vessels supply the gut, nerve cord supply the gut, nerve cord and the body wall. Blood and the body wall. Blood gland are present on the gland are present on the 4,5, and 6 segments.4,5, and 6 segments.

They produce blood cells and They produce blood cells and haemoglobin which is dissolve in haemoglobin which is dissolve in blood plasma.blood plasma.

Blood cells are phagocytic in nature.Blood cells are phagocytic in nature.

Earthworms lack specialised Earthworms lack specialised breathing devices.breathing devices.

Respiratory exchange occurs Respiratory exchange occurs through moist body surface into through moist body surface into their blood stream.their blood stream.