I just googled Fan Worms and they sound interesting. Here is what I found:
IFan Worms are not only beautiful additions to a reef aquarium, but are also efficient filter feeders that play an important role in a properly balanced reef system. Due to their feathery appendages, these worms are also known as Feather Duster Worms. These "feathers" are used to actively filter out tiny organic particulate matter from the water column, often missed by our filtration systems. If these particles are not biologically processed or removed, they slowly decay and compromise water quality. By feeding on these organic particles, Fan Worms keep nutrient levels low and help maintain good water quality.
Fan Worms are marine segmented worms that are sessile, attached to rocks or sand by their base. They are a member of the phylum Annelida, which also includes earthworms
You can find out more just Google Fan Worms.