Department of Zoology at ANDC/Zoology Museum/Museum specimens/Annelida/Pheretima

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Pheretima

Date & Time : 22, October 2017 12:57


Earthworm.jpg

Systematic Position

Phylum: Annelida

Class: Oligochaeta

Genus: Pheretima

Species: posthuma

Common Name: Earthworm

Distribution

Found in moist soil all over the world

Habit and habitat

These are nocturnal in habit and live in damp, moist, humus-rich soil of lawns, gardens etc. In dry weather they burrow deeper into the soil to avoid dryness. Their niche is a herbivore and macro-decomposer and is important as a source of food for birds. It also helps in soil aeration and increasing soil fertility.

Identifying features

Earthworm labelled diagram.jpg
  • Body is long, narrow and cylindrical.
  • Length may reach upto 150 mm.
  • Body colour is brown.
  • Anterior end is pointed while the posterior end is blunt.
  • Body is divided into 100-140 segments called metameres.
  • The anteriormost segment is called Prostomium.
  • Mouth is a crescentic aperture, present at anterior end. The segment containing mouth is called peristomium.
  • Setae are present at all the segments except-1st and last. Each seta is embedded in a setal sac.
  • A glandular band called Clitellum is situated in 14th to 16th segments. It forms coccon during the reproduction.
  • female genital pore is situated in 14th segment (ventral surface)while male genital pore is present in 18th segment.
  • The earthworm feeds on organic matter in the soil.
  • The food is sucked by the pharynx and the oesophageal glands add calcite to neutralise acidity of the soil.
  • The food is then grinded by the horny lining of the gizzard and is absorbed in the intestine.
  • Undigested food material passes out the anus and is deposited as worm castings.
  • The earthworm 'breathes' by the diffusion of gases through its moist skin.
  • The blood contains haemoglobin which transports oxygen throughput the body.
  • Circulatory system is of closed type.
  • Earthworms have no sense organs but they can sense light intensity by small light-sensitive cells found mainly on the uppers skin surface of their body. They can also sense vibrations and chemicals by the means of tactile or chemo-receptors.
  • The earthworms exhibit undulating movement which takes place by alternate contration and relaxation of circular and longitudinal muscles of each segment.
  • Earthworms are hermaphrodites but they reproduce by cross-fertilization.


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