This diatom has capsule-shaped cell walls (also called tests) made of silica. The brownish part is the living cell inside the test. Note also empty tests left behind when a diatom cell dies. These tests are about 55 microns (millionths of a meter) long and about 25 microns wide. Aboard the USCGC Healy in the Makarov Basin. 86.70°, -149.48°.