A dead diatom ?
This diatom appears to be dead. There are brown particles inside, and small organisms go in and out through various openings in its silicate cell wall.
Commentary by Prof. Yuji Tsukii, Hosei University
The shell is all that remains of a diatom that has died. Because of the large number of species of diatoms, we cannot say to which one this shell belongs. If we could observe the shell from the top, side and other angles, it might be easier to figure out, but it is impossible when viewed from only one direction.
Sampling Date : 28 May 2009
Sampling Site : Hirose River B Google Map