Four new small-celled naviculoid diatom species belonging to the genera Adlafia, Chamaepinnularia, Mayamaea, and Microcostatus were found during a survey of the non-marine diatom flora of the South Shetland Islands and James Ross Island (Maritime Antarctic Region). Following both light and scanning electron microscopy, the following species were described as new: Adlafia submuscora sp. nov., Mayamaea josefelsteri Kopalová, Nedbalová & Van de Vijver sp. nov., Microcostatus australoshetlandicus sp. nov. and Chamaepinnularia antarctica sp. nov.
The new species are compared to other morphologically similar species from Europe, South America and the (sub-)Antarctic region. Data on their ecology and biogeography are included.
In addition, the morphology, biogeography and taxonomic position of two other small-celled naviculoid diatoms, Craticula glaberrima (W. & G.S.West) nov. comb. and Sellaphora nana (Hustedt) Lange-Bertalot et al. are discussed.