The spine-bearing diatom Pinnularia sofia Van de Vijver & Le Cohn spec. nov. is described from the sub-Antarctic Heard Island. The morphology of this species was examined using the scanning electron microscopy (SEM). The most striking feature of the new taxon is the presence of three groups of wart-like or spathulate spines that connect adjacent valves to form short chains comprising 2 to 6 individuals. The taxonomical position of the new taxon is discussed, comparing it with similar freshwater Pinnularia taxa present on the same island, such as P. subantarctica (Manguin) Van de Vijver & Le Cohu and its variety elongata (Manguin) Van de Vijver & Le Colu, as well as the elusive P. circumducta Manguin. A short review is made of all spine-bearing and/or colonial Pinnularia taxa described so far. Notes on its ecology are included.