scale bar in image = 10 μm

macroscopic: brown slime on rocks

microscopic: symmetric pennate diatom with obvious transapical costae. There is a raised sternum going through the center of the cell. There is also a rimoportula present on each cell near one apex.

for samples observed by me:
range of lengths: 36-46 μm
range of widths: 12-13 μm
range of costae density: 6-7/10 µm