Annelida: Earthworms | Zoology Optional Notes for UPSC PDF Download

The Environmental Benefits of Earthworms

This article explores how earthworms enhance soil quality, facilitate nutrient cycling, and support plant growth through their unique activities.

Earthworm: Anatomical Structure and Functions

• Earthworms belong to the phylum Annelida, known for their segmented bodies.
• The earthworm's body is composed of approximately 100-150 segments.
• Segmentation enhances their movement, with each segment having muscles and setae (bristles) for control and anchoring.
• Setae ensure that part of the body remains anchored while another part moves forward.
• Independent segment movement allows flexibility and strength during locomotion.

2. Digestive System

• The earthworm's digestive system is composed of several regions, each serving a distinct function.
• Components include the pharynx, esophagus, crop, intestine, and gizzard.
• Food, often soil, enters the mouth and is swallowed by the pharynx.
• The esophagus features calciferous glands that regulate calcium carbonate levels.
• The crop stores food before it enters the gizzard, which grinds it with ingested stones.
• The intestine contains gland cells that release fluids for digestion.
• Blood vessels within the intestinal wall absorb and transport digested food.

3. Circulatory System

• Earthworms have a closed circulatory system that circulates blood through vessels.
• Key components are the aortic arches, dorsal blood vessels, and ventral blood vessels.
• The five pairs of aortic arches function similarly to a human heart, pumping blood into dorsal and ventral vessels.
• Dorsal vessels transport blood to the front of the earthworm, while ventral vessels transport blood to the rear.

Respiratory System

• Earthworms lack lungs and respire through their skin via diffusion.
• Skin must remain moist for efficient oxygen and carbon dioxide exchange.
• To keep their skin moist, earthworms release body fluids and mucus.
• These adaptations require earthworms to inhabit damp or moist soil, often surfacing at night to avoid sun exposure.
• Light-sensitive tissues located on the earthworm's head help them detect light, preventing daytime surface activity.

Earthworm Reproduction

• Earthworms are hermaphrodites, possessing both male and female sex organs, capable of producing sperm and eggs.
• Despite their hermaphroditic nature, most earthworms require a mate for reproduction.
• During mating, two earthworms align themselves in an inverted position for sperm exchange.
• Earthworms have two male openings and two sperm receptacles to receive sperm from their mate.
• Each earthworm possesses a pair of ovaries for egg production.
• The clitellum forms a slime tube around itself, filling with an albuminous fluid.
• As the earthworm moves through the slime tube, it collects eggs from the female pore and sperm (spermatheca) from the male pore.
• Fertilization takes place within the slime tube, which closes as the earthworm exits.
• The closed slime tube becomes an "egg cocoon" placed in the soil.
• Fertilized eggs develop into young worms.

Conclusion

Earthworms play crucial roles in soil aeration, nutrient cycling, and plant health. Understanding their anatomy and reproductive processes sheds light on their importance in ecological systems.