Worms are fairly simple creatures. Physiologically, they aren’t much more than a simple digestive system. Though they also have a lot of the same functioning biological systems has higher animals such as a nervous system, respiratory system, reproductive system, muscles and skin. Below are some of the basics of worm anatomy.
The worm’s outermost body wall is a protective layer called the cuticle but directly beneath this outer layer is the epidermis, similar to our skin. The epidermis contains a host of sensory cells that transmit information to the nerve tissue. Below the skin is a thin layer of nerve tissue that gives the worm a sense of touch. Below that is a layer of ringed and longitudinal muscles that allow the worm to move.
Adult Redworms can have 200 to 400 ringed segments. A set of stacked circular muscles give the worm it’s ring segments and work in concert with a set of longitudinal muscles, contracting and expanding, to give the worm movement. Do you ever wonder why worms can be so difficult to pull out of the ground? Each ring segment has a set of little hair-like appendages, known as setea, which help it move through soil and allow the worm to grip the surrounding soil when grasped by a predator. The setea are very strong and are formed from the same material that makes up our fingernails and the exoskeletons of insects.
The clitellum is part of the reproductive system of clitellates, a subgroup of annelids which contains oligochaetes (earthworms) and hirudineans (leeches). The clitellum is a thick, saddle-like ring found in the epidermis of the worm, usually lighter in color. To form a cocoon for its eggs, the clitellum secretes a viscous fluid. This organ is used in sexual reproduction of some annelids.
Brain and Nervous System
The worm has a simple nerve bundle called the cerebral ganglion which serves as its brain. Along with it’s ventral nerve chord, the worm uses the cerebral ganglion to collect sensory input from the world around them such as light, temperature, moisture and vibrations.
Running the length of the worm’s body is something called the alimentary canal, or gut. It starts with the worms mouth, known as the buccal canal, which has sensory cells allowing the worm to identify food. The pharynx works like a suction pump, pulling food into the digestive system from the mouth. Then food works through the esophagus and into the crop. Worms and birds use their crop in the same way, to store food before it enters the gizzard. The gizzard is the grinder, used to pulverize food particles so they can be digested. Food can then move into the intestine, which takes up nearly two-thirds of the worm’s body and is where final digestion and nutrient absorption occurs before waste is expelled through the anus.
Many tiny organisms, bacteria, fungi, actinomycetes, enzymes and protozoa live in the worm’s gastrointestinal systems aiding digestion. They are microscopic and thrive by the hundreds of thousands within a single worm. These organisms assist in preparing nutrients from the worm’s food to be absorbed by the intestine and utilized by the worm.
The worm’s circulatory system is powered by five valved chambers that regulate blood flow. These are the worm’s hearts and they push blood through a set of blood vessels. The ventral and dorsal vessels carry oxygen rich blood throughout the body. These vessels are also used to transport urinary waste which is diffused through the cuticle. So, next time you pick up a worm just remember that it breathes and urinates through it’s skin.
Worms have no specialized respiratory organs but the do breathe. Oxygen and carbon dioxide are diffused through the skin to and from the circulating blood stream. Lack of moisture in the worm’s environment restricts the breathing process. Prolonged dryness will cause death by suffocation. Exposure to direct sunlight can lead to death in less than three minutes.
When a redworm is sexually immature its body segments are uniform throughout its entire length. As it matures it develops a bulbous gland about one-third of the way down its body called the clitellum. The clitellum produces mucus needed for cocoon production to hold the eggs.
Two worms come together at the clitellum and use their hair-like setae to hold fast to each other. While joined they exchange seminal fluid. At the same time, grooves on the underside of the worm help transport the seminal fluid to the seminal vesicles for later use. Each worm begins to secrete a mucus ring around itself.
After being joined for up to three hours, the worms separate. The mucus on each worm begins to harden as the worm starts to slough off this mucus ring. During the sloughing off process seminal fluid, ovum and amniotic fluid are deposited into the mucus ring. As the ring passes over the worm’s head it seals, forming the lemon-shaped, yellow-colored cocoon. Over a period of weeks, the cocoon hardens to a ruby red color as hatchlings mature.
For use in your Vermiculture Station Lessons, you can download and print this Worm Anatomy Reference Sheet.