The phylogenetic relationships of Prionospio Malmgren, 1867 are estimated in two parsimony analyses. The first analysis includes type and other species of Prionospio (Prionospio) Malmgren. 1867. P. (Minuspio) Foster, 1971, P. (Aquilaspio) Foster, 1971, Apoprionospio Foster, 1969, Aurospio Maciolek, 1981, Paraprionospio Caullery, 1914, Streblospio Webster, 1897, Laubieriellus Maciolek, 1981, and Orthoprionospio Blake & Kudenov, 1978; all members of a group of closely related taxa. Prionospio banyulensis Laubier, 1966 is included as a separate taxon since its relationship to Prionospio has been questioned. The single most parsimonious tree supports monophyly of a group containing P. (Prionospio), P. (Minuspio), P. (Aquilaspio), and Apoprionospio.
Based on the tree topology from the first analysis, 14 species belonging to different subgenera of Prionospio and Apoprionospio are included in a more restricted analysis, with Orthoprionospio cirrformia Blake & Kudenov, 1978 as outgroup. Three equally parsimonious trees were obtained, differing only in the positions of Prionospio ehlersi Fauvel, 1928, Prionospio henriki Hylleberg & Nateewathana, 1990, and Prionospio rugosa Sigvaldadóttir, 1997.
The results of the two analyses are compared to earlier classifications. As support is lacking for monophyly of both subgenera P. (Minuspio) and P. (Aquilaspio), they are synonymized with P. (Prionospio). Apoprionospio cannot be justified as a separate genus without making Prionospio paraphyletic, and is synonymized with Prionospio. Two species, P. banyulensis and P. pilkena Wilson, 1990, are transferred to Aurospio. A checklist of species belonging to Prionospio sensu lato, together with information on type locality and location of type specimens, is included.