Description of Difflugia linearis:
The test is transparent, flask-shaped or elongate pyriform, having a long thin neck with parallel sides and a slightly swollen, rounded aboral region. The surface is sometimes slightly uneven because of projecting particles, but generally it has a regular outline. It is composed of a mixture of flattened pieces of quartz, small whole, flat diatom frustules, fragments of flattish frustules, small siliceous shell plates and round flagellate cysts. Small areas of organic cement, in the form of a network with an open mesh, are occasionally seen. The open mesh has a diameter of about 0.3 microns and walls 0.1 microns thick. The aperture is circular and usually surrounded by small particles. Length 96-108 microns, breadth 32-38 microns, diameter of aperture 12-13 microns.