Mortensen (1950) included only Palaeostoma in the family Palaeostomidae, remarking on the uniqueness of its pentagonal peristome and five triangular plates covering the opening. Ditremaster has a similar pentagonal peristome as juveniles and a similar ethmolytic apical disc with only two gonopores. Both genera further differ from hemiasterids by having the peripetalous fasciole indented by a single interambulacral plate behind the anterior petals. One other genus, Sarsiaster, is also included, based on its similar apical disc and peripetalous fasicole pattern, even though it has a kidney-shaped peristome.
The taxon is treated as a subfamily of Hemiasteridae.
Trachyaster has an ethmolytic apical disc and may belong here, although it retains four gonopores.
Loven, S. 1868. Om Leskia mirabilis Gray. Ofversigt af Kongelige Vetenskaps-Akademiens, Forhandlingar 24 (1867), 431-440.