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The earthworm belongs to a phylum of animals called the Annelids (means ringed worm).
Annelids are worms whose bodies are divided into segments. A segment is like a small
compartment which is almost separated from the next segment. The earthworm has from 80 to
120 segments in its body. Each segment is separated from the next by a thin wall called a
septum. Other worms in the group called Annelids include the leech, sandworm, and the giant
gurgling earthworm.
There are 30-40 different types of worms that are all called by the common name earthworm.
This may include the giant Australian earthworm which grows over inch thick and over seven
feet long! Scientists have solved this problem (thanks to Linnaeus) by giving each type of living
thing a scientific name. The scientific name for the species of earthworm we study and dissect is
Lumbricus terrestris. Remember the scientific name for man is Homo sapiens.
External Anatomy of the Lumbricus terrestris
The bodies of most animals have five basic surfaces. The dorsal surface is the back of top
surface of the animal. The ventral surface is the lower or belly surface. The sides of the animal
are called the lateral surfaces. The anterior surface is the head or front end of the animal while
the posterior surface is the tail or hind most end.
Skin covers the body of the worm and gives off a slimy mucus which coats the worm and
keeps its skin moist. Oxygen dissolves in the wet mucus and goes into the skin of the worm and
then enters tiny blood vessels called capillaries. Thus the worm “breathes” through its skin. If
the moisture on the skin dries out, the worm may suffocate. The skin of this worm is bumpy.
Each lump is a segment separated by a thin wall called a septum.
Short bristle-like hairs are on the ventral side of each segment. These hairs are called setae.
When the setae are extended, they help the slippery worm to crawl or cling into its burrow.
Near the anterior end of the earthworm, a section is larger and has different coloration. This
ring shaped structure is called the clitellum. The clitellum is for reproduction. Earthworms do
not have specific genders. Every worm contains both male and female gonads, but they must
reproduce sexually (with two parents). When reproducing the clitella of both parents give off
mucus. Male sex cells (gametes) from one worm move through the mucus to the female sex cells
(gametes) of the partner. The earthworm’s offspring develop in the soil in special egg cases
called cocoons.
Internal Anatomy of the Lumbricus terrestris
Earthworms eat decayed leaves and materials in the dirt. Soil and food enter the mouth of the
earthworm at the anterior end. The food is pushed in and swallowed by a muscular pharynx and
then enters a food tube called the esophagus. The end of the esophagus opens to a sack used for
storage called the crop. The crop connects with a thick muscular sac called the gizzard. The
gizzard grinds the food. It contains tiny pieces of sand which are rubbed together by muscles in
the gizzard. After the food is ground up it goes to the intestine. The intestine fills the last two
thirds of the body and absorbs nutrients for the body. Soil and waste material then exits the
digestive system through the anus. The waste is called worm castings. Worms help plants by
fertilizing and loosening the soil. They also play an important role in the food chain.
The worm does not have a brain. Instead it has a primitive structure made up of a group of
nerve cells. It is called a ganglion. The ganglion of the worm is located just above the pharynx.
The ganglion allows the worm to respond to light, touch, and chemicals in the soil.
The circulatory system of the earthworm has ten hearts which are found in pairs. The five
pairs of hearts loop around the esophagus and pump blood. The ventral blood vessel is located
on the belly or ventral side of the worm. Blood moves through the ventral blood vessels from the
hearts to the posterior part of the animal. Smaller blood vessels called capillaries supply each
cell with oxygen, food, and water. The dorsal blood vessel located near the back of the worm
carries blood from the posterior to the anterior part of the worm.
The earthworm is a cold blooded animal. This means that this animal cannot control or
maintain a constant body temperature. The body temperature of the worm is about the same as its
surroundings.
Lumbricus terrestris - Review
1. Define :
* Annelid –
* segment* septum –
2. The scientific name for the earthworm is ______________ ______________.
3. The scientific name for man is _________________ _________________.
4. Label the surfaces:
5. Explain how the Lumbricus terrestris breathes. Include the terms skin, mucus, capillaries,
and oxygen in your explanation.
6. Anatomy means _____________________________________________________.
7. External means _____________________________________________________.
8. Internal means ______________________________________________________.
9. What are setae? What are they used for? Can they always be seen?
10. What is the function of the clitellum?
11. How can you tell the male from the female earthworm (trick question!)?
12. Where do the young earthworms develop?
13. Explain what each organ or opening of the digestive system does.
* mouth –
*pharynx –
*esophagus –
*crop –
*gizzard –
*intestine –
*anus –
14. How are earthworms beneficial (helpful) for the environment?
15. What is a ganglion? What are three things the ganglion controls?
16. How many hearts does the Lumbricus terrestris have?
17. Name the four parts of the circulatory system of an earthworm.
18. Explain the difference between a cold blooded and a warm blooded animal.
earthworm cold blooded or warm blooded?
19. Define septum.
Is the
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