Explain Class Oligochaeta - Earthworms in details?
This group of annelids includes the earthworms. Oligochaetes live in the soil or in fresh water habitats, and a few inhabit marine environments. The name "oligochaete"; is derived from the Greek words "oligo," which means few, and "chaetae," which means "long hair." Each body segment contains appendages of bristle-like hairs, which are also known as "setae."; Setae are used to anchor the worm, as well as to aid in movement. Earthworms ingest soil, and process whatever food components are contained within the soil in their digestive tract. What isn't absorbed passes out through the anus and is deposited on top of the burrow as "castings."
Earthworms have an interesting method of reproducing sexually. Since they are hermaphroditic, both partners become fertilized at the same time during copulation, or sexual union. Each worm receives and stores sperm from its partner. Following separation, a thickened portion of each worm called the clitellum secretes a mucous envelope containing unfertilized eggs. This envelope passes over the pore in which sperm was previously deposited, fertilizing the eggs as the envelope passes by. The envelope then forms a mucous cocoon around the fertilized eggs until they hatch.
Asexual reproduction can also occur in earthworms. If the tip of an earthworm gets cut off, the worm will regenerate a new tip, as long as the lost tip involves no more than seven segments.