Aeolosoma - The strangest worm in the world?

Aeolosoma is a genus of annelid worms like earthworms. But unlike earthworms, these are much smaller and can be found in different freshwater habitats like ponds and streams in many parts of the world. But it's not just in nature you are able to find these as they also inhabit almost all freshwater aquariums, and probably also a huge part of unchlorinated pools. In aquariums they are introduced with food or plants and can sometimes be found in extremely large numbers.

Even though they might look a bit scary and poisonous with their orange spots and long spikes, they are completely harmless to humans. They feed on decaying plant material, microalgae and other microorganisms and the way they do this is a bit strange. These worms are known as suction-feeders, which means that they use their mouths as a vacuum cleaner to get their food. When they find something they want to ingest, they surround it with their mouth and tiny beating projection inside the mouth then creates a vacuum that sucks up the food. And if the vacuum cleaner mouth wasn't weird enough for you, this might be.

When Aeolosoma worms reproduce they almost always do it asexually by growing a genetic clone of themselves. The clone starts to take form from the tail end of the parent worm and then slowly turns into a separate organism. Towards the end it looks like the daughter worm is biting its parent in the tail. Sometimes several clones can be developing at once leaving a chain of the parent worm and its clones.

A single mature worm is at most 2 mm long, but the chains of unseparated clones can be up to 10 mm long and looks a bit like a small and thin piece of hair without a microscope. The orange spots covering the worm are a collection of lipids forming these colourful drops of oil. Here they are orange, but in other species they can both be green, blue, red and colourless. Not much research has been done on these colourful oils and their function is not clear. Maybe they serve as an energy-storage. Maybe they are helpful in scaring of predators. Or maybe a combination of the two or something entirely different.