The type species of the monotypic Polyzoniida genus Dawydoffia Attems, 1953, D. kalonota Attems, 1953 from Vietnam, is redescribed based on type material. A second species of the genus, D. siphonocryptida n. sp., is described from Laos based on scanning electron microscopy, micro-computed tomography and molecular barcoding. The species of Dawydoffia are among the shortest and widest of the Polyzoniida, and resemble in habitus those of the Siphonocryptida genus Siphonocryptus Pocock, 1894, both having pleurites that are completely fused to the tergites. Dawydoffia was previously placed in the family Siphonotidae Cook, 1895, but can be identified as a member of the Holarctic Hirudisomatidae Silvestri, 1896 based on the following morphological characters: the uplifted posterior margins of the tergites, the collum covering part of the head, the position of the male gonapophysis or pseudopenis, the retracted telson, and the ozopores situated close to the tergal margin. However, both Dawydoffia species have a slender paronychium, a character previously known only from the Siphonotidae, but also documented here for Hirudisoma roseum (Victor, 1839). A slight redefinition of the Polyzoniida families is provided. The two Dawydoffia species differ in their coloration, as well as in their somatic and gonopodal characters.