The closest relatives based on 16S rRNA gene similarity are Xylanivirga thermophila (83.57%), Christensenella hongkongensis (83.57%), Caldicoprobacter guelmensis (83.41%), and Caldicoprobacter faecalis (83.29%). POCP values to all close relatives were below 30% and GTDB-Tk placement assigned the type species to an unknown genus within ‘f_CAG-552’. Separation from the other proposed species Pumilibacter muris and Pumilibacter intestinalis within the propose novel family Pumilibacteraceae (see protologue below) was confirmed by phylogenomic placement, which showed they were distinct from each other, and by the POCP value of 45.9% between the type species of each genus. The type species is Anaerocaecibacter muris.