Unearthing Earthworms

Daniel Liao 4/9/14 PAP Bio-Period 6

Objectives

Students will:

  • Learn about the external and internal structure of the earthworm
  • Focus on the organs, structures, and functions of the circulatory system
  • Understand more about the ecological role of the earthworm.

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The Taxonomy of an Earthworm

  • Kingdom: Animalia - eukaryotic, multicellular
  • Phylum: Annelida - body made up of segments separated by a septum
  • Class: Clitellata - clitellum (secretes clitella or cocoon during reproduction)
  • Subclass: Oligochaeta - setae, no lateral appendages
  • Order: Opisthopora - terrestrial worms, paired testes
  • Family: Lumbricidae - largest earthworm family, contains 33 species of earthworms
  • Genus: Lumbricus
  • Species: terrestris

More about the Earthly Earthworm:

Commonly known to mankind as the earthworm, the species Lumbricus terrestris is a common species of worm that is round, and typically is 7-8 inches long, though some have been recorded to have grown to a length of over 14 inches. The earthworm is part of the phylum of worms known as Annelida, because of the earthworm's body segmentation. Comprised of about 100-150 segments, called annuli, the earthworm has small bristles called setae attached to each segment, which allows for the earthworm to move, and burrow into the soil where it lives. Nicknamed 'nightcrawlers' because they burrow during the day and only come to the surface to feed and mate at night, earthworms can burrow up to 6.5 feet deep into the ground during the daytime, feeding on decomposing organic matter on the surface of the soil. Because earthworms consume dead and decaying matter, earthworms are classified as decomposers. Earthworms are extremely important to the environment, as they, through burrowing, mix the soil and fertilize it with excremented waste. Earthworms are hermaphrodites, meaning that they have both male and female reproductive systems at once. However, although being hermaphroditic, earthworms do not self-fertilize or reproduce asexually, instead going to the surface of the soil to mate and exchange sperm with other earthworms. Predators of the earthworm include birds, rats, toads, and frogs.

Evolutionary History

Earthworms are known for being hardy and resilient, being able to develop tolerance for extremely high levels of contaminant or toxic materials within the earthworm's natural habitat. It has been suggested that the earthworm developed segments and some duplicates of certain body parts, like the heart, due to the fact that earthworms once failed to separate during reproduction and fused together, possessing the organs and body systems of both. Another theory for the evolution of segments on an earthworm is simply that genetic code for a single segment was duplicated and repeated multiple times, resulting in a multi-segmented body. The earthworm has developed a distinct head and tightly fused 'brain' through a process known as cephalisation.
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Human Impact

Earthworms are commonly known to us as useful gardening helpers. Earthworms have been and still are crucial to fertile crop soil and healthy land. In some cases, indigenous populations valued earthworms highly due to their usefulness in agriculture and farming. Unfortunately, now, many farmers use pesticides to cleanse their fields of pests, but unwittingly cleanse their fields of earthworms as well. Some people have suggested that, in times of great crisis or in a case requiring survival, to eat earthworms. The earthworm has been valued as a great source of protein, which is also partially why the earthworm has so many predators.

The Dissection, Internal, and External Anatomy of our Little Worm Friend

The earthworm possesses a closed circulatory system, meaning that blood is recirculated throughout the body. Earthworms lack lungs, but absorbs oxygen through the skin. The oxygen travels along the dorsal blood vessel, then through the five aortic arches (the earthworm's hearts) where the oxygen-enriched blood is pumped back throughout the body. Small blood vessels that can be found in each segment redirects oxygen-depleted blood back to the dorsal blood vessel, where the process is repeated. For a complete dissection and detailed external anatomy analysis, view the video below. Diagrams can also be found below.
Earthworm Dissection