How To ID The Aquarium Hitchhiker – Linopherus (Polychaete)

You might be wondering what Polychaete actually means, and if you didn’t already know, it is a family of worms. There are around 8000 different living species of worm that are currently known, and Polychaetes can include ring worms, lugworms, bloodworms, sea mice, and much more. These are all marine worms that are known for their well-defined segmentation of the body.

These worms specifically are called Linopherus, and you will probably discover them residing in your tank without notice at some point within your fishkeeping journey. Aquarium hitchhikers are pretty common, and often mean that your tank is well established and has a good amount of healthy bacteria within it. Some are good and beneficial and some are really bad and will cause problems for you aquarium and fish community. Fortunately, Linopherus Worms are good and benefial saltwater hitchhikers.

Appearance and Behavior

What Do They Look Like And How Big Are They?

Something that is unique about them is that most Polychaete body segments will have a pair of parapodia, which are flat outgrowths that have tiny bristles on them. They can vary in size from just a few millimeters to around 3 meters in length, and they are typically divided into two groups.

These groups are the errantia, or free-moving forms, and the sedentaria, or tube-dwelling forms.

What Are They?

For those that are wondering, a Linopherus is actually just a common type of bristleworm that is usually thought to be Eurythoe sp. However, this is not the case, as they are actually a Linopherus sp. If you are wondering what all this means, we are going to explain it below to help you gain a better understanding.

Differences Between Other Bristle Worms

One of the best ways to find out if something is not a Eurythoe is through the characteristic that makes it stand out as different. This characteristic is its eyes, as the common bristle worm has two wandering eyes that you will easily be able to notice.

On the other hand, Eurythoe do not have any eyes, which is quite disturbing. So, this is one of the easiest ways to tell the difference between the two. Another thing that you can look out for are gills, and this is due to the fact that the Eurythoe have impressive gills, whereas the Linopherus do not. The gills of the Eurythoe are very prominent, but the gills of the Linopherus are hardly noticeable at all.

Touching Their Spines

Another way to tell that you might not want to put to the test would be to touch both of them. The spines of the Eurythoe are much more likely to stick into you than those of the Linopherus. You would probably be able to handle the Linopherus without any issues at all when it comes to their spines, but you probably won’t have the same luck with the Eurythoe, which is why you probably wouldn’t want to try this out yourself. If you did try to do this, you would likely find that your hands became impaled by bristleworm spines.

What To Do If You Get Stung

If you do ever find yourself in this situation, you should dip the affected area into vinegar. It doesn’t particularly matter what type of vinegar you use, but you will need to hold the affected area in the vinegar until the spines dissolved. It won’t usually take that long, so you will be free of these spines in no time.


Linopherus are great to have when they are present in the right numbers, but you should consider what fish you are keeping them with to make sure that you have a good match.