it is very rare species, better go for DNA sequence, you will get idea

Maybe a pluricellular microorganism? Animal? Sample was collected on a phototrophic biofilm mainly composed by Chlorophyta (Chlorella, Bracteacoccus, Scenedesmus...) using a sterile swab.

II think is a unicellular organism. Maybe a ciliate or a rotifera – many of them feed on microorganisms

It looks like a helminth ( pluricellular) and not a single cell.

I am not an expert on this subject but can be a cyanobacteria?

Ask the cave man living there......

I think it's a bit too big for your average bacteria (it looks in the order of 15-25 um). I actually agree with Ana Sampaio; to me it looks like a rotifera, but it would be a very small one! Good luck

Hi,

It looks like a rotifera (as per Ana's suggestion), but must to say, rotifera are multicellular animals with a complex structure (internal). So this maybe to small for that. It maybe interesting to see how many of these organisms are present in a sample.

For a nice web resource about rotifera:

http://www.ucmp.berkeley.edu/phyla/rotifera/rotifera.html

rosalba