Morphometric shape analysis and ultrastructural data are provided for six genodemes of the Sellaphora pupula species complex that have been studied during the last 20 years from Blackford Pond, Edinburgh, UK. The demes have previously been shown to be separated by prezygotic reproductive barriers: cells of different demes do not pair, though they may show residual interactions when sexualized. A new morphometric method, contour segment analysis, which was recently developed for diatoms in relation to automated identification, gives a clear separation of all six genodemes and indicates no heterogeneity within each. Legendre shape analysis gives less separation in this instance. All other available data, including molecular sequence data, also support separation of the six demes at species level. Five new species are therefore described: S. auldreekie, S. blackfordensis, S. capitata, S. lanceolata and S. obesa. The identity of S. pupula sensu stricto is clarified through designation of epitypes.