Annelids, this lesson you’ll learn about how

Annelids, or segmented worms, reproduce both sexually and asexually depending on the species. In this lesson you’ll learn about how some of the different annelids and how they reproduce.

What Are Annelids?

Pop quiz: What is an annelid? Your first answer may be ‘I have no idea!’ but chances are good that you already know the answer to this question. Annelids are the organisms that belong to the phylum Annelida and if you’ve ever seen a wiggly earthworm, you’ve seen an annelid. These creatures can be very tiny (1 mm long) or very large (as long as three meters!), and they live in many different places including the soil, but also in both freshwater and saltwater environments.

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Annelids also come in many different forms, such as the earthworm you are familiar with, as well as leeches and the incredibly beautiful polychaetes.

Annelid Reproduction

But what we’re here to discuss today is not how cool annelids are–we’re more interested here in how they reproduce. Annelids are really interesting in this regard because they may reproduce sexually or asexually, depending on the species.

For example, sexually reproducing earthworms are hermaphroditic, meaning that they have both male and female reproductive parts. But this doesn’t mean that they self-fertilize; instead they meet up, align their bodies in opposite directions, and exchange sperm. This sperm is later collected by a cocoon of mucus that works its way up the outside of the worm’s body, which also collects that worm’s own eggs, fertilizes them, and then that cocoon ends up in the soil which is where the future worms-to-be develop.

Earthworms reproduce sexually by aligning their bodies and exchanging sperm.
earthworm reproduction

On the other hand, polychaetes, which are mostly marine, reproduce asexually.

One way they might do this is by fission, which is when the worm makes an exact copy of its DNA and then splits into two. It basically clones itself into a new individual! These worms might also reproduce by budding, which is when a smaller fragment breaks off (but still has the same DNA as the ‘parent’ worm) and becomes a new individual. In budding, the new individual isn’t the same size as the parent–it’s a smaller fragment that will eventually grow into a full-size individual.

Polychaetes are beautiful marine worms that reproduce asexually.
polychaete tube worm

Like earthworms, leeches are also hermaphroditic and reproduce sexually but the process is a bit different.

These guys meet up and exchange sperm like earthworms but the fertilization is internal. So the sperm fertilizes the eggs and the cocoon develops to protect those eggs, but instead of dropping it off in the soil, leeches will care for that cocoon and the unborn babies inside. It’s not clear why they do this–it may be for protection, but whatever the reason, there’s a lot more parenting going on here for sure.

Leeches reproduce sexually and offer a surprising amount of parental care.
leech

Lesson Summary

The phylum Annelida, which includes the earthworms, polychaetes, and leeches, is full of cool and interesting animals.

These segmented worms are found in all sorts of environments, from soil to freshwater to saltwater. They come in all shapes and sizes, ranging from the very small to the very large, and from black to bright beautiful colors.Annelids are also fascinating in how they reproduce. Some reproduce sexually while other reproduce asexually. Those that reproduce sexually, like earthworms and leeches, are hermaphrodites, meaning that they have both male and female reproductive parts.

It does not mean that they self-fertilize; they still need another worm to complete the process. For those that reproduce asexually, like the polychaetes, they may do so by fission or budding. Fission produces an exact copy of the original worm by copying the DNA and splitting the worm in two. Budding occurs when a fragment of the worm is broken off and a new individual develops from that smaller piece.

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