- Earthworm is a reddish-brown terrestrial invertebrate that inhabits the upper layer of moist soil.
- During day time, they live in burrows made by boring and swallowing the soil.
- Common Indian earthworms: Pheretima and Lumbricus.
Morphology of Earthworm
- Earthworms have long segmented cylindrical body.
- Number of segments (metameres): about 100-120.
- Dorsal surface has a dark median mid dorsal line (dorsal blood vessel) along the longitudinal axis of the body.
- First segment (peristomium or buccal segment) bears the mouth. A lobe called prostomium covers the mouth.
- Prostomium is sensory in function and is used to force open cracks in the soil into which the earthworm may crawl.
- In a mature worm, segments 14-16 are covered by a dark band of glandular tissue called clitellum.
- Body has 3 regions: preclitellar, clitellar & postclitellar.
- 4 pairs of spermathecal apertures are found on ventro-lateral sides of intersegmental grooves (5th -9th segments).
- A single female genital pore is present in the mid-ventral line of 14th segment.
- A pair of male genital pores is present on the ventro-lateral sides of the 18th segment.
- Many minute nephridiopores open on the body surface.
- All segments except the first, last, and clitellum bear S-shaped setae, embedded in the epidermal pits. Setae can be extended or retracted. Their function is locomotion.
