Excellent Earthworms

Earthworm Dissection Lab by Katherine Lee; Vu P1

Objectives

The purpose of the earthworm dissection is for students to learn the structures and functions of segmented organisms, particularly annelids. The viewer will learn about both the external and internal anatomy of an earthworm, focusing mainly on the digestive system.

Background Information

Taxonmy:
  • Kingdom- Animalia
  • Phylum- Annelida
  • Class- Clitellata
  • Subclass- Oligochaeta
  • Order- Haplotaxida
  • Family- Lumbricidae
  • Genus- Lumbricus
  • Species- terrestris


Predator-Prey Relationships:

Earthworms play an important role in breaking down dead or decaying organic matter. To do so earthworms eat dead and decaying plant matter breaking it down into smaller pieces, allowing bacteria and fungi to feed on it and release the nutrients into the soil. Earthworms have many know predators including snakes, birds, moles, shrews, frogs, and centipedes. Snails feed on the cocoons of earthworms and mites feed on the eggs of an earthworm.


Habitat & Niche:

Earthworms live all over the world with some living in mud by freshwater, some live under the sea, but most live on land. They need moist soil conditions and decaying matter to survive. The majority of earthworms live about a meter or so from the surface where most of the dead/decaying matter is. Earthworms are soil-dwelling detritivores who aid in breaking down organic matter and releasing nutrients back into the soil.


Adaptations:

  • Each segment of an earthworm's body has setae or bristly hairs that help them move through the soil
  • Due to earthworm's lack of vision and hearing they are very sensitive to vibrations
  • Earthworms secrete mucus that helps them moves through soil. When making burrows this mucus keeps the walls from collapsing.
  • In order to get food an earthworm must push its pharynx out of its mouth and grab hold of the food.


Fun Facts:

  • Some species of earthworms can live up to eight years old but it is very rare.
  • In North America the biggest earthworms are about 30 centimeters long but in Australia some have grown to 2 meters long.
  • The longest earthworm ever recorded was found in South Africa and measured 22 feet long.
  • Earthworms do not have any locomotive organs, they move by constant muscle contracting and relaxing.
  • Although an earthworm has both male and female sex organs, reproduction occurs via cross-fertilization.
  • Earthworms have the ability to regenerate small segments of their body.
  • Even though earthworms lack a nose and eyes they are still able to detect light and vibrations. They communicate with each other through touch and taste.
  • There are over 2,700 different species of earthworms.

Digestive System of an Earthworm

The digestive system of an earthworm consists of - in order - the mouth, pharynx, esophagus, crop, gizzard, intestine, and the anus.


  • Mouth- The mouth is the first part of the digestive system that takes food into to the body. Since earthworms have no teeth soil particles help "chew" the food.
  • Pharynx- Food is lubricated by a mucus secretions to make the it easier for it to pass through the earthworm's body.
  • Esophagus- After the food passes through the pharynx calcium carbonate is added to the mixture to neutralize the acids in the food.
  • Crop- Food is temporarily stored in the crop where it is mixed before moving on to the gizzard.
  • Gizzard- The powerful muscles of the gizzard mix and grind the food until it is a thick paste. Then the glands of the walls of the gizzard add enzymes to help with the chemical breakdown of the food.
  • Intestine- The intestine contains friendly bacteria that eats the food mixture and releases vitamins, minerals, carbohydrates, and proteins that the worm will absorb into its body. Blood vessels that line the intestine help absorb the liquefied food.
  • Anus- After it passes through the intestine soil particles and undigested material pass through the opening known as the anus.

How do Earthworms Affect You?

Earthworms help to break down dead and decaying matter through the process of decomposition. This releases the nutrients in the organic material back into the soil making them available to living plants. When nutrients are released, it fertilizes the soil. Earthworms are also responsible for adding organic matter into the soil and mixing soil layers.