As a living being, a worm is a composite of various moving parts. While worms may seem very simple on the surface, there is actually a lot more doing on in your worm’s body than you might imagine.
They not only have multiple body segments, but also have blood vessels, a circulatory system, and a variety of different cells and functions beneath the skin. It is easy to assume that worms live with very few inner workings.
Yes, a worm is a living entity and all living entities have at least one cell. Their simplistic outer shape actually masks a more complex range of cell activity taking place inside their body. But how does everything function together? What type of cells do adult worms likely possess, and are earthworms any different?
Is a Worm Made of Cells?
Yes, just as with all other living things, a worm is made of cells to an extent.
However, the types of cells these organisms have really will vary compared to other creatures.
Therefore, while it’s fair to say that worms are made of cells, we need to consider their types and functions.
How Many Cells Does a Worm Have?
There is no exact answer, as different types and species of worm have different cell numbers.
However, the simplest worm species is one that has been used for experimental research for well over a decade, and is worth looking at as an example.
The C. Elegans worm is transparent, and is only a single millimetre long. Nonetheless, it has 302 neuron cells that connect to between 5,000 and 7,000 synapses.
By comparison, the human brain has 100 billion neurons connected to 100 trillion synapses – even so, that is a lot of inner working.
Specifically, males had 1,031. The males also had 81 more neurons in their tails.
Other worm species have greater numbers of cells and as with all species, much depends on age, health and availability of food to sustain healthy weight and size.
There are over 8,000 species of worm. Of that number, only 3,500 species have been classified after study.
What we do know, however, is that all species of worms have collections of special cells with clearly defined roles in their bodies. Let’s take a look at those in the next section.
What Type of Cells Do Worms Have?
Let’s take a look at the most common worm cell types one by one.
- The skin of earthworms is made of epithelial cells. Coating these is a slimy mucus, which entraps air from the atmosphere and allows them to breathe through the skin.
Just as we humans require oxygen to be transported throughout our bodies in the bloodstream, and carbon dioxide expelled, so do worms.
Indeed, unlike other animals, researchers have found that worms absorb oxygen through tissues in their skin. Human skin, of course, has a different purpose.
- Earthworms also transport oxygen in red blood cells. A protein called haemoglobin transports the gases just as humans transport oxygen in our bloodstream.
Earthworm blood cells are red for the same reason as ours – we both have haemoglobin.
- Earthworms can be killed quickly, sometimes within seconds, by exposure to ultraviolet light. Although worms do not have eyes, earthworms have photosensitive cells to enable them to change direction away from danger.
- Interestingly, some worms, but not all, have both male and female sex organs. Two worms mate by joining ‘clitella’ and exchanging sperm.
When laying eggs, it is known that worms seek out ideal locations for eggs to be maintained at a suitable temperature, not near excessive water or strong light. Their reproductive system is a little more complex than ours in some ways.
- Beneath a worm’s single-layered epidermis cells are circular muscles made of cells that help worms to move via contraction.
Changing direction, for example away from sunlight, is prompted by stimulating receptors. Earthworms can actively seek out other earthworm companions in this way.
- Worms also have nerve cells and respond to various stimuli. It is also now recognized that worms feel pain, too.
This isn’t to the extent a human brain can anticipate pain and/or suffer the same trauma – but it is now accepted that worms have greater sensitivity to pain, such as being hooked on a fishing line, than was once thought possible.
- It was assumed that the brains of worms were so unsophisticated that the display of reactions to pain were movements in response to other stimuli.
For example, if a worm is cut in half, both parts squirm. Often one part dies quickly whilst the other part may wriggle away. It is now understood that a nerve sensing trauma results in a form of stress. Therefore, you are likely causing a worm serious distress if you cut it in half, and that applies to most worms, not just the segmented worms you are likely to see in the mud.
Is a Worm Single Celled?
No. Worms are well-known for being multicellular.
For example, their various organs and structures are formed from distinguishable cells.
The cerebral ganglia or brain cells, for example, control the body of the worm and the worm’s response to various simulations.
Segmented worms such as earthworms are usually made up of at least 1,000 cells with a third of those being nerve cells. A further third are somatic cells. They are far from being one-cell wonders.
Worms remain some of the most deeply fascinating creatures on earth. While a worm may not seem to be a complex animal, it has incredible biology.
Even embryonic worms are closely studied to help us learn more about how these creatures exist and thrive in the wild.
It is easy to assume that a worm will only have a simple cell structure, but they are much more complicated beneath the skin.
They have a particular excretory system, longitudinal muscles, and need various cells to help keep pumping blood forward.
So, yes – worms are many-celled, and like us, they have lots of intriguing characteristics that we are only just starting to learn about.