Hydrodictyon reticulatum or water net cells aggregate to form colonies or mats.

colonies or mats are

  •  a single-layered membrane or sac-like network of several thousand cells
  • free-floating or secondarily attached
  • reaching over 50cm long 
  • meshes clearly visible in large colonies

Cells are

  • cylindrical to oblong-oval, up to 15mm long
  • 2-4 adjacent cells connected by their edges and forming 5-6-sided meshes