Elegant Earthworms

Venu Kantamani 04/07/14 Vu - PAP Bio - Period 4

Background Information

Lumbricus terrestris, more commonly known as the earthworm, belongs to the kingdom Animalia under the phylum Annelida, class Oligochaeta, order Opisthopora, and family Lumbricidae. The earthworm has an interesting niche: it aerates and fertilizes the soil. Without earthworms, the soil would not be nearly as fertile or good for growing plants. They bring organic matter down into their burrows from the surface and secrete it to form worm casts. Its main intake of food comes from this organic matter from the surface. Its main predators are the New Zealand flatworm (Arthurdendyus triangulatus) and the Australian flatworm (Australoplana sanguinea), both of which have been accidentally introduced to much of the rest of the world. The earthworm has had many ecological adaptations including segmentation, having a closed circulatory system, and having a complete digestive track.

Objectives

Through this dissection lab, students are to learn the structures and functions and observe the external and internal structure of the earthworm.

Digestive System

The digestive system of the earthworm primarily consists of the mouth, pharynx, esophagus, crop, gizzard, intestine, and anus. The decaying organic matter the earthworm ingests enters through the mouth and passes through the pharynx and esophagus. The esophagus passes the food through the crop, a thin-walled sac that holds soil before it is passed to the gizzard. The thick-walled gizzard grinds the organic matter into small pieces, so that the nutrients can be absorbed as they pass through the intestine. Any remaining undigested food and soil are excreted through the anus.

Interesting Facts

Earthworms go by a multitude of other names including dew worm, squirrel tail, twachel, or night crawler. They are native to and extremely common in Europe but have been introduced in many parts of the world. All earthworms are hermaphrodites meaning that they contain both the male and female reproductive organs.