Dark algae ID?

[Necrodaemus]

Does anyone know what this stuff is? It’s covering only a small area on the uppermost rock and has grown into the recesses of this Monti cap that I mounted a few weeks ago. I don’t think it’s cyano as it’s very difficult to remove. It feels slippery/rubbery, and it’s thin.

 

[Dan_P]

Does anyone know what this stuff is? It’s covering only a small area on the uppermost rock and has grown into the recesses of this Monti cap that I mounted a few weeks ago. I don’t think it’s cyano as it’s very difficult to remove. It feels slippery/rubbery, and it’s thin.

If it hard, could be a red coralline algae. If soft and slimy cyanobacteria