The ciliate family Cyrtolophosididae Stokes, 1888 contains species that are poorly known from both the morphological and molecular perspectives. To further our understanding of this family, one species, Aristerostoma marinum Kahl, 1931 , was redescribed. Cells in our population had a mean in vivo size of 15×8 μm. There were six rows of somatic kineties, as well as six dorsal kinetids belonging to sparsely ciliated somatic kineties. The oral apparatus comprised a bipartite paroral membrane and four adoral organelles. The optimal ecological tolerances for pH and O2 matched those of the environment in which the specimens were collected, but were different for salinity and temperature. To further test the phylogenetic placement of the family Cyrtolophosididae with increased taxon sampling, the small subunit rDNA of three morphospecies was characterized: A. marinum, Aristerostoma sp. ATCC 50986 and Pseudocyrtolophopsis alpestris. Unconstrained and constrained molecular analyses supported the non-monophyly of the order Cyrtolophosidida. The family Cyrtolophosididae fell out separately from the rest of its order. Haplotypes from previous environmental studies were also placed in a phylogenetic context within the class Colpodea.