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Earthworm

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Classification Kingdom – Animalia

Phylum – Annelida
Class – oligochaeta
Genus – Pheretima
Species – posthuma
Common name – earthworm
New name – Metaphire posthuma

Habit and habitat 

  • Cosmopolitan in distribution.
  • The earthworms are burrowers.
  • They are found in the soil rich in decaying organic matters usually in gardens, pastures, lawns, irrigated farm lands, near the banks of the ponds, lakes and rivers.
  • They do not prefer to live in sandy, clay and acid soils which are deficient in organic matters.
  • Nocturnal in habit.
  • Friend of farmer – make soil porous and fertile by their castings.
  • Generally inhabit within 30 to 45 cm depth and reach up to 3 meters depth to find moisture or to avoid dryness of body surface.

External Features– visible from outside.


  

  • Shape and size – by symmetrical, cylindrical and elongated.
  • Anterior end is tapering or pointed than posterior.
  • Size about 150mm × 5mm.
  • Coloration – brown due to porphyrin pigment. I
  • It is darker on dorsal surface than ventral. This pigment avoids dryness from sunlight and makes easy to respiration.
  • Segmentation – metamerically segmentation i.e. external segments corresponds to internal segments. The segments are called metameres. The body of earthworm consists of 100 to 120 segments.
  • Setae – are S - shaped locomotory organs of earthworm found on equator line on each segments except 1st last and clitellum. Each seta half embedded in body wall and projected backward from body surface.
  • Other locomotory organs are musculature and hydraulic skeleton.
  • Clitellum -- is a thick collar or girdle like glandular organ situated on 14th 15th and 16th segments. It divide the body into three parts – preclitellar (1st to 13th), clitellar and post clitellar regions (17th to last segments).
  • About body wall – three layers.. Cuticle, epidermis, and musculature.
  • External apertures are mouth, genital openings (male and female), anus, spermathecal pores, genital papillae, dorsal pores, nephridial pores etc. 

Detailed View of Earthworm

  • Mouth is Situated in 1st segment below muscular boring organ prostomium, crescentic aperture. Large amount of humus soil is ingested by mouth.
  • Genital openings
    a. Male (one pair) g. o. are situated in 18th segment ventro – laterally. Male reproductive discharges are passed through the apertures.
    b. Female (single) g.o. is situated in 14th segment midventrally.
    Ova are passed out through the aperture.
  • Spermathecal apertures or pores (4 pairs) are situated between 5/6, 6/7, 7/8 and 8/9 segments ventro-laterally. sperms are collected during copulation between two earthworms.
  • Genital papillae (two pairs) are situated in 17th and 19th segments ventro-laterally.
    They help in copulation.
  • Dorsal pores are situated along mid dorsal line after 12th segment except last segments and opens into the body cavity. White coelomic fluid is oozes out through these pores to keep moist the body.
  • Nephridiopores are very minute large number of pores situated throughout the body except 1st three segments. Actually, these are pores of integumentary nephridia.
  • Anus is a small vertical aperture situated at last segment. Undigested food is passed out through the pore as castings.