During an expedition to King George Island, Antarctic Peninsula, we discovered two species of organic-walled, monothalamous foraminifera bearing mineral particles within their cytoplasm. The particles are predominantly magnetite and titanoferous magnetite. Both species are phylogenetically related and belong to a clade of monothalamous foraminifera having in common the ability to ingest mineral grains. One of the species, described here as Psammophaga magnetica sp. nov., has an elongate organic test and mineral particles located near the aperture. According to the analyses of partial small subunit ribosomal DNA (SSU rDNA), the species may have a panantarctic distribution and is slightly different from a similar Arctic morphotype. The second species is morphologically and genetically similar to Allogromia crystallifera Dahlgren, 1962 from Scandinavian fjords. Because the genus Allogromia is distantly related to Psammophagidae, we have transferred this species to the genus Psammophaga. In several specimens of this species, we found SSU rDNA sequences closely related, but not identical, to Hippocrepinella hirudinea (Heron-Allen and Earland, 1932), another monothalamous foraminifer present at the same sampling site. The origin of these extraneous sequences is unclear and raises the question of authenticity of rRNA gene sequences in some foraminifera.