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Nematode Reproductory System

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Like other animals, nematodes, or roundworms, need to reproduce to pass on their genetic information to the next generation. In this lesson we'll discuss the reproductive system of nematodes. You might be surprised at what you learn!

What are Nematodes?

Commonly referred to as the roundworms, nematodes (Phylum Nematoda) are a diverse and widespread group of animals. They can be found just about anywhere on Earth, and there may be as many as half a million different species that exist today. Some are parasitic, meaning that they live off of another organism, while others are free-living, meaning that they do not depend on another organism for their survival.

Despite their great diversity, their body plans are actually quite similar. Most nematodes look alike in that they are long, thin creatures with a mouth on one end and an anus on the other. Their bodies are covered by a protective layer called the cuticle, which they shed every once in a while, much like our skin cells fall off and are replaced over time.

But what I want to specifically discuss with you today is the reproductive system of nematodes. Like other animals, nematodes need to reproduce in order to create the next generation of individuals. These individuals carry the parent's genetic information, pass it on to their offspring, and so on and so forth.

Nematode Reproductive Structures

Unlike some other types of worms (earthworms, for example), nematodes are mostly dioecious. This means that the males and females are distinctly different from each other, much like human males and females - does it surprise you to learn that we're more like these worms than you might have originally thought?) One of the main differences we see is that males are much smaller than females. This is because the females are charged with producing large amounts of eggs, so they need a larger body to do so. Additionally, while males have only one opening for both reproduction and removal of bodily waste products, females have a separate opening for each.

But outward appearances aren't the only differences among the sexes, and you might be even more surprised in the continued similarities to reproductive structures that you are already familiar with. In most dioecious species of nematodes, the females have two ovaries which are connected by oviducts to two different uteri (uteri is plural for uterus), a vulva and vagina, as well as a seminal receptacle that stores sperm from a male. The one vagina leads to both uteri and is covered by a special flap made of that body cuticle I mentioned before.

The male spicule is used to inject sperm into the female
nematode spicule

Male nematodes on the other hand have one or two testes and a spicule, which is a long structure used during mating that injects sperm into the female's reproductive tract. And here we find the cuticle playing an important role yet again, as this is what the spicule is made of. Talk about mutli-purpose! In addition to these parts the males may also have a seminal vesicle where the sperm is made, a vas deferens, which is the path along with the sperm travels, and a cloaca, which is where the sperm eventually leaves the body. As we learned before, this opening in males also serves as rectum where waste products leave the body.

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