I think you are right it should be a species of Gloeocapsa from Chroococcales since it is a colony embedded in a matrix within a common sheath. I would suggest to take better and clear images for confirming the species.
May refer :
1.Süsswasserflora von Mitteleuropa, Bd 19/1: Cyanoprokaryota: Chroococcales (by Jirí Komárek and Konstantinos Anagnostidis)