Calothrix forms slippery mats of tangled filaments that attach to rock surfaces, seen on the boulders in the mid-section of the picture above. Click on the image for a closer view. Each filament is composed of a line of cells that secrete a sticky, mucus-like sheath. The sheath reduces contact between the cell and the outside environment protecting against desiccation and the effects of rapidly changing salinity that would occur after a heavy rain. The mucus, in addition to the basal cell, helps hold the filament securely to the rock surface. All that mucus makes walking in this zone difficult. For a microscopic look at Calothrix, click on the image to the right.