Unearthing the Earthworm

Earthworm Dissection - Mitcham-PAPBio-2 - Irina Didenko

BackGROUND Facts

An earthworms scientific name is Lumbricus terrestris. It is part of the kingdom Animalia and phylum Annelida. It is a tube like creature made up of segmented parts and is an invertebrate that lives in soil and obtains its energy from the nutrients in the organic matter in the soil. Worms range in size from seven to thirty five centimeters and can be found in North America, Europe and Russia where there are many forests with rich soils. Earthworms help the environment by aerating the soil, processing organic matter to enrich the soil and is a food source for birds, snakes and even fish (as bait!).

Evolutionary Earthworms

This cladogram shows that earthworms are quite evolved organisms. Based on the diagram we can find out more about the characteristics that they posses which include multiple cells (multicellular organism), tissues, bilateral symmetry, protostome (mouth before anus), coelum and segmentation. You can find a picture of them right under Annelida.

Obvious Objectives

We, the students, dissect the earthworm in order to become more familiar with the external and internal anatomy of the animal. It is also an easy and compact model to know the basic makeup of the anatomy of any creature.

Dissection

Earthworm Anatomy

Digging in the DIGESTIVE system

The digestive system of an earthworm is one of its biggest and most important systems because the intestine takes up more than half of the worms body. The organs making up this system are located mainly in the anterior part and include the intestine, gizzard, crop, esophagus, pharynx, and mouth. The worm moves through the soil by sucking it into its mouth, and passing it through the pharynx which allows the soil to be swallowed. The earthworm does not have teeth so it must use the particles in the soil to grind up the food. After the pharynx, the soil enters the esophagus where calcium carbonate is released to neutralize the acids in the soil. Afterwards it goes to the crop and gizzard where the digesting starts to take place. Next the soil enters the long digestive tract, which takes up the majority of its body, where the soil is digested with the needed nutrients absorbed and excess removed through the anus at the other side of the body. The waste is called a casting and is sometimes used as plant fertilizer!

Human impact on Earthworms

Humans are one of the biggest predators of earthworms. When people commit deforestation and cut down forests it really hurts the earthworms because there is no more organic matter. All of the animals are gone as well as the leaves from trees providing nothing to decompose. Earthworms disappear from these environments leaving weak, thin and sandy land cover unable to sustain any life.

EARTHWORMS ARE IN THE NEWS!

FUN FACTS!!!

  • Earthworms have both testes and ovaries and are called hermaphrodites.
  • The earthworm has bilateral symmetry which means it has two halves that are almost identical (left and right).
  • The earthworm has no respiratory system and preforms its gas exchange through its skin.
  • An earthworms wastes (also know as castings) are used as fertilizer to enrich the soil.
  • Earthworms contain pairs of excretory structures which function as kidneys and are called niphridia.

SOCIETY DEDICATED TO THE STUDY OF EARTHWORMS

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