Who would be building a sand tower?!

[haleyf1024]

My live rock is from Florida, and I have already found tons of hutch hikers, most being serpents and tons of crabs. Now, between two rocks someone has built a tower out if sand and similar things (pieces of shell, rock, etc. stuff found in live sand). It is between 2 rocks that lay on top of each other. Who would be building this? My rock has been in my system for months and this is the first time I have seen something like this. I recently added a maxima clam and a zebra turbo, but thats it in the last month or so. Known hitch hikers I have found are: red mithrax, gorilla crab, porcelain crab, decorator grab, tons of micro serpent stars, bristle worms, a couple medusa worms, various coral and pods, and clams. Could it be from the emerald and red mithrax? They have bred and had 2-3 babies survive who also live under this rock.

 

[haleyf1024]

the tower is in the side of the picture. It's hard to get a photo because of where it is

 

[haleyf1024]

I actually saw what built it. It was a reddish worm, but not a bristle worm. It was smoother and appeared to have the same head as a medusa. Do medusa worms build towers?!

 

[kacrocorals581]

I don't see what mound you're talking about but probably a spaghetti worm they build mounds in sand