Virtual Dissection Lab

Earthworm

Background Information

Most people know earthworms as those squiggly things in the soil. Earthworms play a major role in their environment and are the reason we can have such luscious gardens. Earthworms break down decaying plant matter, their waste is extremely fertile, and their tunnels aerate the soil allowing root systems to grow better. Earthworms are hermaphrodites meaning they have both male and female organs. Their offspring are wrapped in a cocoon that protects them until they hatch.

Objective

Today we will initiate the dissection of an ordinary earthworm. Take a look at the worms external anatomy. You can see this organism is segmented and has a clitellum that produces mucus to lubricate the body. Pin down the anterior and posterior end of the earthworm, then begin cutting from the clitellum to the mouth of the organism. Make sure not to damage the internal organs while cutting. Afterwards, pin back the flaps of sin and observe the internal anatomy. One more thing is that the dorsal side is gray while the ventral side is white so make sure you cut along the ventral side. Lets begin looking at the organs on the anterior end of the organism. The digestive system starts at the mouth to the pharynx then the esophagus afterwards the crop, which acts as a stomach, then the gizzard that causes the physical break down of food. The intestine is then after the gizzard where waste is. The large flesh orbs you see are seminal vesicles those are male gonads. Then the small nodes are seminal receptacles that are the female parts. This shows they are hermaphroditic. The darker ringed organ is the heart, each ring is an aortic arch. Behind these organs is the dorsal vessel that carries blood through the animal
Earthworm Anatomy

Earthworm Circulatory System

Earthworms have a simple close circulatory system, meaning the blood is contained inside the organism. A group of aortic arches act as the heart and constrict the dorsal vessel pumping blood throughout the organism. The blood from the dorsal blood vessel goes to the ventral blood vessel which then completes the circulatory loop. The dorsal blood vessel supplies the dorsal side with blood and the ventral blood vessel supplies the ventral side with blood.

Taxonomy

Phylum: Annelida


Class: Clitellata


Order: Haplotaxida


Family: Lambricicdae


Genus: Lumbricus


Species: Terrestris

Evolution

Earthworms are a very basic and primitive creature. They have no skeletal system, no brain, not even a true heart. The earthworm does have cilia which are small external hairs that help with locomotion and a simple closed vascular system. Earthworms are also hermaphrodites having both male and female parts. Their segmentation puts them in phylum Annelida and their clitellum puts them in class clitellata.

Ecology

Earthworms play an amazing role in their ecosystem. They are a reliable food source and an efficient decomposer. Their populations so are easy to maintain that their are captive worm farms for gardening. Earthworms break down decaying plant matter and produce nutrient rich waste for plant soil. Their tunneling breaks up the soil for plant roots and helps to aerate the soil. Earthworms are hermaphrodites and produce cocoons in which their eggs are laid. After a period of time the miniature versions of their adults climb out and begin to grow. Birds and many other animals prey on worms or indirectly eat the plants they help to grow. All in all they are key to their ecosystem

Body Systems

Earthworms has a circulatory, excretory, reproductive, and digestive systems. The circulatory system consists of the aortic arches and the dorsal and ventral vessels. The aortic arches act as hearts and constrict the vessels moving blood through the organism. The excretory system consists of the intestines and the anus. The intestines stretch the length of the organism until the waste is excreted by the anus. Worms are hermaphrodites and contain seminal vesicles and receptacles which produce reproductive gametes. The digestive system consists of the mouth, esophagus, crop, and gizzard. The crop holds the food and the gizzard performs the mechanical breakdown of the food.

Human Impact

Their is little to no human impact on worms. They are no where near close to being extinct and their common in any backyard. They are so easy to cultivate their are worm farms that breed them. The only factors that effect their population is predation and soil pollution. The predation is cause by both natural and invasive predators and the soil pollution is caused by human intervention. The more devastating one would be soil pollution because it would kill off the entire population of worms allowing no recovery.

Fun Facts

  • Their are about 2,700 different kinds of earthworms
  • One acre of land can house more than a million worms
  • the largest earthworm was in south America at 22 feet long
  • Charles Darwin Spent 39 years studying earthworms