Template:POTD/2023-05-11
Pinnularia is a genus of freshwater algae in the class Bacillariophyceae, the diatoms. An elongated elliptical unicellular organism, it is usually found in ponds and moist soil. The cell walls are composed chiefly of pectic substances on a rigid silica framework, and are composed of two halves known as thecae (or, less formally, valves). This Pinnularia major specimen, about 0.3 millimetres (0.012 in) in length, was photographed through a light microscope.Photograph credit: Anatoly Mikhaltsov