Aeolosoma

Aeolosoma are very small annelid freshwater worms found all over the world. Even though these worms have been known for almost 200 years we do not know much about them. In fact, we know so little that there is still uncertainty on how to spell its name. Some will spell it aeolosoma, while others spell it aelosoma. 

Another mystery yet to be solved is which class of worm it is. Some place it in the same class as earthworms, the oligochaetes. Others place them in the polychaetes with bristle worms, and still others think they belong to their own separate class on the taxonomic tree of life. However it seems like the majority describes them as polychaetes.

Video showing aeolosoma at different magnifications with different microscopy techniques. 

Notice the almost complete clone in the back end of the worm

But instead of focusing on the things we do not know, here are some things we do know about this strange and tiny worm:

• Aeolosomas are mostly well under 5 mm in length, but some have been observed to grow to around 10 mm. 
• The worm is covered in tiny orange dots which are oil droplets. These can vary in color from deep orange/red to yellow and even greenish. However, these droplets are poorly researched, and their function is not well understood or described, but could be used for storage of energy.
• Aeolosomas feed on microalgae and other microorganisms. When they feed, they use their mouth like a vacuum cleaner, sucking up food to be ingested. Worms that feed like this are called suction-feeding worms.
• These worms replicate in an asexual manner the vast majority of the time, which is done in a quite strange way. When a worm is ready to reproduce, it starts to grow a clone in the rear end. When the clone is complete, the two worms separate and live their own life.