Unidentified tiny calcareous disc

[Tomoko Schum]

I am wondering what thes tiny discs are. They are about 3 mm in diameter and probably 0.3 to 0.5 mm thick. They grow on hard objects and not on any tissue. They attach a tiny part of their discs on shells and other hard object and flip around in water current. They get dislodged soon and collects on the sand bed. I wonder if they may be some sort of foraminifera.

 

[ProudSoonersFan]

Is it a pileolaria? I have those all over my tank and refugium. They won't come off with my scrubber either.

 

[Tomoko Schum]

No, it's not pileolaria which is a type of tubeworm. These are more like bivalves. They get dislodged from glass or other hard surface very easily. They collect in low flow areas.

 

[markkazdad]

Nice photo and good game of stump the chump going here.

Do they move other than by being dislodged?

 

[Tomoko Schum]

Thanks, Mark.

The tiny shell just blows off in a strong current. A number of them attach themselves on the backs of a fighting conch and Atlantic cone snails, but when I try to collect them, they tend to fall off the shell. They don't seem to do any harm or I have not noticed any damage done by them so far. They just make my white sand bed tan colored at parts.