They are easily mistaken for filamentous brown seaweeds when viewed with the naked eye, and they can be as large, but even under low magnification the diatoms become apparent. In tropical waters, brownish intertidal cyanophytes are macroscopically similar to some of the tube-dwelling diatom colonies. Most species form a single tube around the cluster of diatoms, but one species, Parlibellus berkeleyi , has tubes within tubes, each with a single row of diatoms. Growth of the tube seems to be at the tip.
Cells seem generally able to migrate within the tube.
Cells are about 50 micrometers long. Cells are about 60 micrometers long. The species involved are scattered among several genera. Most are naviculoid and do not have very distinctive silica shells, but they do form fairly distinctive colonies. Some species appear to cohabit tubes made by others.