The epipelic habitat has a unique community of diatoms associated with it. One component of this community is the conspicuously large diatoms, 1-200 um long, that possess a keel. In Lake Kathrine, these keeled forms are able to move on the surface of the benthic mud-detritus mat that covers the lake bottom. In mid to late June, portions of this mat float to the surface, allowing easy sampling without perturbation of the community. Nitzschia sigmoidea, Entomoneis ornata, Campylodiscus noricus, Cymatopleura cochlea, C. solea and several Surirella species were examined while living, showing distinct movement patterns. Scanning electron microscope observations show a similar raphe system and a diverse valve morphology among these diatoms.