Slit-like canal (raphe) running down the centre of the cell surface, on at least one of the two cell faces.
Slit-like canal running down the edge of the cell face (may be difficult to see directly, but striations can be seen at one edge).
Slit like canals totally absent.
![[Diploneis], Cluthe River, X1600. Photo: Otago Regional Council & Manaaki Whenua](/assets/Tools-And-Resources/Identification/algae/diploneis2__FillMaxWzMwMCwyMDBd.jpg)
![[Surirella], Lake Rotoroa, Hamilton, X640. Photo: Manaaki Whenua](/assets/Tools-And-Resources/Identification/algae/surirella5__FillMaxWzMwMCwyMDBd.jpg)
![[Asterionella], Lake Rotorangi, X400. Photo: Manaaki Whenua](/assets/Tools-And-Resources/Identification/algae/asterionella2__FillMaxWzMwMCwyMDBd.jpg)