One of the things you'll often times find in your tank are tube worms. They extend feathery appendages to filter feed particulates from the water, just like the larger Featherdusters that come from Fiji or Hawaii. These two are very small, found at the base of some zoanthids in my tank. They can spread on their own, but usually they arrive as hitchhikers. The larger one on the left creates a hardened white tube that is very easy to see in your rockwork. Reef-safe.