Earthworm Dissection: Digestive

Nelson Ly, Period 4, Guzman

Objectives

We're dissecting earthworms to learn the structure and form of an annelid's digestive system.

Background Information

  • Scientific Name: Lumbricus terrestris
  • Habitat: Meadow, woods, stream banks, lawns, (etc.)
  • Predators: ants, mites, centipedes, earwigs, nematodes, fly larvae, termites, springtails, snails, slugs, spiders, birds, rats, mice, moles, toads, turtles, and snakes.
  • Prey: None
  • Ecological Niche: Decomposer/ Herbivore
  • Ecological Adaptations: They breathe through their skin, so they must stay moist. They regenerate themselves if cut from the tail side. Even though they don't have eyes, they can sense light from their anterior end.

Pictures/ Videos

Interesting Facts

  • Earthworms come in a variety—around 6,000 species worldwide.
  • Each earthworm is both male and female, producing both eggs and sperm.
  • They consume their own weight every 24 hours.
  • They can grow up to 10 feet long.
  • Earthworms can have from 100-150 segments.
  • The largest earthworm ever found was in South Africa and measured 22 feet from its nose to the tip of its tail.

  • In one acre of land, there can be more than a million earthworms.

Body System Focus: Digestive

  • 1. Crop - food storage
  • 2. Mouth - opening for food to enter
  • 3. Pharynx - muscle to suck in food (dirt)
  • 4. Intestine - digestion of food
  • 5. Gizzard - grinding food
  • 6. Anus - where wastes exit
  • 7. Esophagus - tube where food is passed from mouth to crop
  • 8. Pharyngeal Muscles - supports pharynx, sucks in food

Earthworms eat by pulling food into their mouth with their prostomium combined with the muscular pharynx which creates a very high suction (like a vacuum). The food is stored in the crop and then ground up into small pieces in the gizzard. Earthworms need a gizzard because they do not have any teeth. The nutrients are absorbed into the body in the small intestine.

Cross Unit Content

Taxonomy

•Kingdom: Animalia


•Phylum: Annelida


•Class: Clitellata


•Order: Haplotaxida


•Family: Lambricicdae


•Genus: Lumbricus


•Species: Terrestris

Human Impact

Earthworms are considered very important in soil organic matter cycling. Certain species are responsible for burying surface residue, while other species are actively involved in the decomposition process, making available important nutrients for other living organisms in the soil - like plants.

Earthworms have some negative traits as well, in certain areas introduced species have created competition for native earthworms. This makes it very difficult for native species to live successfully and even survive, native species frequently exist in small isolated areas.

Evolution

The phylum Annelida is made up of segmented worms, numbering about 15,000 species. Body segmentation, a trait of annelids, was a major step in the evolution of animals. Annelids are protostomes, meaning they have a coelom made from cell masses. This coelom is divided into a series of repeated parts.