Phylum : Annelida

Class : Oligochaeta       

Order : Terricolar

Family : Megascolecidae

Genus : Pheretima

Species : Portuma

  • Earthworm, also known by other names like night crauless fishing forms and rain worm is a reddish brown terrestrial invertebrate that live in the upper layer of soil.
  • By swallowing and boring  in soil, they made bursoues and live their in day time.
  • Their faecal deposits is known as worm castings.
  • Common species in India are – Pherltima and lumbricus.

Morphology of Earthwarm:-

  1. Form :- It has long, narrow, cylindrical body without appendages anterior end is painted but no distinct  head and posterior head is rounded.
  2. Size:- adult worm is about 150mm long and 3-5 mm wide.
  3. Color :- dark median line is present and dorsal surface is darker than ventral surface.
  4. Symmetry:- Bilateral.
  5. Segmentation :- Circular groves are present on body known as annuli.
  • These are 100-120 segments present on earthworm’s body.
  • The body is divided internally into a series of compartments by transverse partitions known as septa.
  • Metamesic segmentation is present in earthworm as external segmentation of body by annuli is largely corresponds to internal division by septa.
  1. Clitellum :- Segments 14,15,16 is surrounded by glandular bond known as clitellum or cingulum.
  • Material for the formation for the formation of egg case is secreted by clitellum.
  • Setae are the sing of small, chitinous bristles present on middle of segment except first and last.
  • Setae can be extended or retracted, their principle role in locomotion.
  1. Apertures :- many external apertures are found in earthworm’s body

Mouth :- Peristomium is a cresenctic aperture at anterior end of first segment.

Dorsal edge of peristomium project forward above mouth as small, fleshy lobe called prostromium. It lacks sensory appendages and not a true sengment.

Anus :- at the posterior end of last segment, slit-like aputerr can e seen. This s anal segment.

Female genital pose :- Eggs pass out from the body through a opening present on ventral side of 14th segment.

Male genital pose :- Exit of the sperms from body is done through fair of small openings situated on small popillar present on ventral side of 18th segment.

Apertures of Accessory glands :- Genital or copulatory popillar are present  on 17th and 19th segment bears a papillar and fine apertures of accessory glands.

Spumathecal pores :- apertures lead to spumathercal and serve to receive sperms from another worm during capulation are known as spermathecal pores, situated ventrolaterally in grooves b/w segments 5 and 6, 6 and 7, 7 and 8 and 8 and 9.

Dorsal pores :-  The minute, sphinetered holes, present along the mid-dorsal line in intersegmental groves. These holes lead to coelom, and help in keeping the skin moist.

Nephridiophores:- They are scattered irregularly over all segments except first two and act as excretory organ in earthworm.

Anatomy of Earthworm

  • Body wall of earthworm consists of :-

Outer layer : Epidermis

Middle layer : Circular muscle, longitaclinal muscle

Inner layer : colonics epithelium.

  • Secretory glands are present of epidermis which mainly composed of columnar epithelium.

Digestive system :-

  • In earthworm, alimentary canal is a straight tube runs b/w from very 1st segment to last segment.
  • The mouth at terminal end opens into buccal cavity, extends from first to the middle of 3rd segment followed by pharynx. Pharynx opens into oesophagus, narrow tube in segments 5-7.
  • After oesophagus , gizzard comes which nerves to grind decaying organic matter ( 8-9 segment.)
  • The stomach (8 or 9-14 segment ) is a narrow, glandular tube. Its calcium glands neutralizes humic acid present in humus.
  • The intestine start from 15 segment to last segment and opens into anus.
  • Internal median fold of clorsal  wall is present b/w  26-35 segments known as typhlosole, which helps on increasing the surface area for absorption.
  • Digestive enrymes break down complex food into smaller absorbable units when ingested food passes through digestive tract.
  • These simpler molecular are absorbed through intestinal membranes and utilized.
  • Anus expels the faecal matter.

Respiratory system :-

Earthworm respires through cutameous respiration i.e. exchange of gases through skin.

Due to immense varcularity of skin, exchange of gases occur from moist surface into this blood steam.

Circulatory system :-

  • Closed types of blood vascular system is followed by earthworm.
  • It consist of heart, blood circulating in one direction.
  • Blood glands are present on the 4th,5th and 6th segment and produce blood cells and haemoglobin.
  • Blood cells acts like phagocytes.

Excretory system :-

Nephridia, they coiled tubules, are responsible for excretion and osmoregulatin. It is of 3 types :-

  1. Pharyngeal nephridia :-
  • Occur in 3 pair in 4 to 6 segments.
  • They discharge excretory matter into gut by paired ducts.
  1. Septal nephridia :-

Occur behind segments 15 on anterior and posterior surfaces of all septa. They did same as pharyngeal nephridia via septal excretory ducts. Thus , enteronephsic.

  1. Integument Nephrda :- Attached to inner surface in all segments except first two.
  • They discharge waste matter to exterior by nephredophores.
  • Thus, exonephric.
  • Excretory matter : Urea.

Nervous system:-

Ganglia are arranged segment wise on ventral paired nerve cord. (3-4 segments )

  • Nerve ring is formed by nerve cord enciveling pharynx and joins cerebral ganglia.
  • Cerebral ganglia along with nerves in ring integrate muscular and sensory actions.
  • Receptor cells are present on organs for light and touch to feel the vibrations and to distinguish light intensities.
  • Sense organs are located on anterior part of worm.
  • Chemoreceptor are present in worm which react to chemical stimuli.

Reproductive system:-

  • Earthworm is hermaphroclite ( bisexual ).
  • Protandry i.e. maturation of testes earlier than ovaries excludes self fertilization.
  1. Female reproductive organ
  • On 13 segment, pair of ovaries is present attached to the septum b/w 12 and 13.
  • Sperm thecae, 4 pair of sacs on segment 6 to 9 receive and store spermatozoa during copulation.
  • Oviducts pair which start from ovarian funnels in 13 segment open out at female genital pore present on 14th segment ventral surface.
  1. Male reproductive organ :-
  • On segment 10 and 11, two pairs of testis are present in testis sac.
  • On segment 11 and 12, two pair of seminal vesicles are present.
  • In segments 10 and 11, two pairs o vasa differentia start from seminal funnels extend to segment 18, when they join prostatic ducts.
  • On ventral side of segment 18, a pair of common prostatic  and spermatic ducts open out at male genital pores.
  • Segments 17 and 20, irregular prostrate glands are present.
  • On segments 17 and 19, accessory glands are located which open out by fine ducts on genital papillae.

Vermi composting :- the process of increasing fertility of soil by earthworms is called vermin composting. Earthworms make borrows in soil and make it power which helps in respiration and penetration of developing plant roots.

Related Keywords
11    PMT    Biology    Structural Organisation in Animals    Earthworm