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.
The links are to photos on other pages on this site. Temperate shores, especially during the spring bloom time, may have abundant colonies, but they are often short-lived. In tropical areas it is more common to find them as small epiphytes, but the tropical regions have been very poorly studied to date. I studied them on the east coast of Canada and the west coast of North America, and I've seen some in the tropics. Eileen Cox studied them in Britain.