Date & Time : 22, October 2017 12:57
Common Name: Earthworm
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.
- Body is long, narrow and cylindrical.
- Length may reach upto 150 mm.
- 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.