There are too many types of worms for me to be comfortable in this world. Although I am a biologist, I’m just not down with the worms and some of the scary things in the arthropod phyla (spiders, ticks, scorpions). This picture here shows a nice and diverse collection of the worms that span three full phyla of the nine available phyla. That’s a lot of vermes, as the picture names them. But, these phyla don’t include just the old earthworm, oh no. There are parasites, enormous tube worms of the deepAway from the surface of the body. ocean, and other fun things like leeches.
Flatworms
Also known by the Latin name Platyhelminthes, literally meaning flat worm. There are non-parasitic flatworms called Planarians. These are basically herbivores, feeding on algae. In their headRounded proximal end that fits into the acetabulum of the hip bone. region, they have a cluster of nervous tissue and not really eyes, but eyecups that can sense light. Their mouthThe opening of the digestive tract where food enters and mastication begins. is in the middle of their body and it emerges with their extendable pharynxThe muscular passageway connecting the mouth to the esophagus and larynx. or throat. Once they consume food it is digested in their gastrovascular cavity, which is not just an open sac, but now a tract with lots of little pockets to increase surface area.
This category includes a whole bunch of parasites that are both horrifying and fascinating. Let’s start with blood flukes. This little worm, tapered at both ends, is transferred from a snail host. These worms take hold in small capillariesThe smallest blood vessels where gas, nutrient, and waste exchange occurs between blood and tissues. of your mesenteries, sheets of fat the bind together all your guts. These sheets contain blood vessels taking nutrients from the food in your small intestine and depositing it into the hepatic portal system. This system brings this nutrient-rich blood to the liverA large organ that produces bile, detoxifies blood, and stores nutrients., where it is cleansed before being released to the rest of the body. But, none of that happens because these worms absorb all those nutrients bound for your hepatic portal system, starving you from the inside. After that, do I need to go on?
Acanthocaphalan and Hymenolepis are genera that contain straight-up, make-me-lose-10-pounds, GI tract parasites. These things are genius. They have these hooks to help them grab onto the wall of your small intestine and embed themselves in a way that will eliminate expulsion. With Hymenolepis, pieces of it will come out with your fecesSolid waste material formed in the large intestine and expelled through the anus., making you think you are ridding yourself of this worm. You are not. It’s just a small small piece of what is probably 10 feet long.
Roundworms
This group, also known as nematodes, includes hookworm, pinworm, heartworm, and all the things you don’t want for yourself or your animals. So cook your pork fully, and please get your dogs heartworm protection. So important. Although most of these are pathogenic to humans, there are some that exist in soil as a natural form of IPM. Caenorhabditis elegans is one such species that has constantly served as a model organismA living individual made up of cells. for everything from nicotine studies to space flight research.
Nematodes have one blunt end and one tapered end. Inside them, is just a long tube of a digestive cavity and reproductive organs. As an organism, I mean, all you really need to do is eat and reproduce. What’s interesting about their digestive cavity is that it has two openings. In different parts, it does different tasks such as mixing and churning near the mouth and absorption near the excretory opening. Kind of like human stomachs (mix and churn) and intestine (absorb). Ever see Spaceballs? What’s all that bubbling and churning? That’s Mr. Coffee. Oh, I always have coffee with my radar.
Segmented Worms
Annelids are the worms with which you probably have the most experience. These are segmented worms. This phylum includes leeches, the giant tube worms at the hydrothermal vents, and the marine worms polychaetes. I do not like polychaetes like the pink ribbon worm. Most annelids live in waterThe universal solvent essential for life., but earthworms are the terrestrial annelids. Important for your gardens…they aerate the soil.
Let’s look at earthworms as an example for annelid anatomyThe study of the structure of the human body.. These organisms have bristles for walking, but also mucus-secreting organs to reduce friction as they drag themselves along the ground. They move by the alternating contractions of a circular muscle layer and a longitudinal muscle layer. So they have this inch-worm like motion. As they contract these muscle layers, they create pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. differences to move blood through their blood vessels. They don’t really have a heart, but these enlargements of blood vessels surrounding the gastrointestinal tube.
They have a nervous systemThe organ system that controls body functions using electrical and chemical signals. that has these clusters of nervous tissue at the head and what seem like a long piece of nervous tissue that runs down the belly of the worm….hmmm….like a spinal cordThe central nervous system structure that relays signals between the brain and body. does.
Worm respirationThe process of gas exchange, including ventilation, external and internal respiration. is not that efficient, but since the worm is so tiny, this method works pretty well. The respiratory surface for the worm is their skinThe body’s largest organ, providing protection and regulation., of which you can see a cross section A cut or slice of the body or an organ for study. here. In contrast, the human respiratory surface is the lung (or the alveoliMicroscopic air sacs in the lungs where gas exchange occurs between air and blood. of the lung). As blood deoxygenated blood flows to the surface of the worm, oxygen is pickup and carbon dioxide is dropped off. The oxygenated blood is then moved to the interior of the body. This respiratory surface has a very low surface area to volume ratio, but it is efficient enough for the tiny worm.
Let’s talk marine worms for a moment here. They are fascinating.
List of terms
- deep
- head
- mouth
- pharynx
- capillaries
- liver
- feces
- organism
- water
- anatomy
- pressure
- nervous system
- spinal cord
- respiration
- skin
- section
- alveoli