Bacteria come in all shapes and sizes. Bacterial cells tend to be about one tenth the size of a eukaryotic cell, which works out as around 0.5 to 5 micrometers in length. This is far too small to see with the naked eye (a micrometer is 1/1000 of 1/1000 of a meter!). Of course there are exceptions to this rule, and there are a couple of types of bacteria that are up to half a millimetre long - these species are called Thiomargarita namibiensis and Epulopiscium fishelsoni (note that we always write the names of bacteria in italic letters).
Lots of bacteria is spherical in shape and we call this morphology a coccus (or cocci plural). Rod-shaped bacteria are known as bacilli. While these two shapes make up most kinds of bacteria, others can be spirals, comma-shaped or exist as long filaments. Many species are found as single cells, while others like to associate with each other. For example, some hang around in pairs, others in chains and some clump in groups that look like little bunches of grapes. Others might even form dense aggregations known as biofilms or bacterial mats. You might have seen these mats as a slimy coating on damp rock faces.
