Worm Anatomy

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Worm Anatomy 2017-03-11T14:04:27+00:00

Worms! Worms! Worms!
Everything you ever wanted to know (or didn’t) about earthworms

Worms are complex

According to Ronald E. Gaddie, Sr., and Donald E. Douglas, “[i]f there were a scale of increasing animal complexity from the lowly protozoa to insects or vertebrates, the earthworm would occupy the top position on the scale.” Why do they and many others feel that way? Because earthworms have highly-developed digestive, excretory, nervous, reproductive, muscular, and closed-loop circulatory systems. How do they work?
The amazing anatomy of worms makes them the best thing to have in your garden!

Lots of worms!

Healthy worms have a nice maroon color and are often iridescent.

Digestive systems make pH balanced fertilizer

Digestive – simply put, earthworms eat dirt. Earthworms have an alimentary (food) canal, a tube that extends from mouth to anus. The worm processes both organic and inorganic material in this muscular digestive tract. It digests most of the organic debris and organisms, but the food and inorganic material it does not digest is excreted through the anus as castings (worm manure). Glands within the esophagus excrete calcium carbonate that converts acidic materials, such as leaves, into castings with a basic or almost neutral pH. The alimentary canal also produces enzymes beneficial to soil and plants. This process explains the superiority of worm castings to all other natural fertilizers.

Worm poop isn’t really “waste”

Excretory – each segment of an earthworm except the first three and the last segments have a pair of excretory organs comparable to humans’ kidneys. The waste material excreted through these organs results in the “slimy” or moist coating on the skin of an earthworm. Thus, what is excreted through the anus as castings is not technically “waste” material.

Worms “think” faster than humans

Nervous – An earthworm does indeed have a brain. However, removal of the brain has little effect on its behavior. For the most part, the brain responds to sensations of light and touch. Two structures called ganglia are the actual control centers. The earthworm lacks definite eyes, but light-sensitive cells within the body wall detect light (which is generally accompanied by unwanted heat) and send it burrowing into any darkness available. Unlike a central nervous system that begins with a sensory nerve ending that transmits a signal to a brain that, in turn, transmits a signal back for movement, the earthworm’s double nerve cord produces a much quicker response since the entire body responds instantly to stimulation received on any segment of the body.

Worms make babies too

Reproductive – Earthworms are hermaphrodites, that is, they have both male and female reproductive organs. However, it still takes two to tango. They will line up next to each other, heading in opposite directions (make of that what you will), and create a mucus layer that becomes an enclosed channel, allowing sperm to travel into seminal receptacles in each “reciprocating” earthworm. A cocoon is formed on the clitellum band of each earthworm. Each earthworm backs out of its cocoon, depositing both eggs and sperm into the cocoon as it does so. The cocoon closes at each end, fertilization occurs, and anywhere from two to twenty offspring will hatch from within the cocoon.

How worms move around

Muscular – an earthworm moves through a complex procedure. Under the epidermis are two layers of muscle, one circular (going around the worm like a belt) and one longitudinal (running down the length of the worm). Its skin is also covered with almost imperceptible bristles (setae), four pairs per segment, that it uses to anchor some of its segments while other segments advance. The circular muscles contract and the earthworm elongates. When the circular muscles relax, the longitudinal muscles contract and shorten the earthworm, then it anchors its tail, contracts its circular muscles, elongates, and moves forward. Rinse and repeat. And repeat.

Worms with lots of heart

Circulatory – five hearts; need I say more? Well, I will. Its system is very similar to that found in humans. Five pairs of aortic arches (hearts) pump oxygenated blood through a main vessel and to the capillaries. In the capillaries, food and water are exchanged for waste, and the blood then returns to the heart to repeat the process.

Do worms breathe?

Respiratory – earthworms do not have lungs. Instead, the capillaries lie just beneath the outer covering, and respiration occurs by diffusion through the surface of the body. This fact explains why earthworms come out of the ground during a heavy rain. Because earthworms breathe through their skin, excessive amounts of water in the soil after a heavy rain will drown them. Conversely, if they dry out, they are unable to carry on respiration and will die. Therefore, earthworms like moist but not soaked soil.

Each of these systems should inspire some appreciation for the “lowly” earthworm!

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