Type species: Cosmochthonius (Nortonchthonius) oblongisetosus n. sp.

Diagnosis — Species belonging to the genus Cosmochthonius with the posterior pygidium truncated and the large dorsal setae that project far away from the margin of the hysterosomal plate in a ’skirt’ fashion, the first setae of the hysterosomal segment H (h1) and first adanal (ad1) which are strongly modified, with the look of ’cabbage leaves’ (Figure 1).

Remarks — This new subgenus, known solely by one species, shows the appearance and layout of the dorsal series of notochaetae c-f of Cosmochthonius. It differs from the other genera of the polydactyl group of Cosmochthoniidae in that the shelled expanded dorsal setae of Krivolutskiella and the erectil and foliar setae of Phyllozetes lack, and by the unguicular formulae, which are 2-2- 2- 3 in Phyllozetes and 2-2-2- 2 in Krivolutskiella. Taking into account the body size and the growth of the erectile setae, the new subgenus occupies a position close to Cosmochthonius s. str. because they lack the body miniaturization and/or the reduction or regression of the erectile setae, that defines Cosmochthonius (Nanochthonius) Subías and Gil-Martín, 1995 type species Cosmochthonius (Microchthonius) ruizi Kahwash, Subías and Ruíz, 1989. The modification of the posterior hysterosomal setae in this species, particularly that of the h1 and ad1 setae justified the creation of the new subgenus Cosmochthonius (Nortonchthonius).

Etymology — The subgeneric ’ Nortonchthonius ’ name is dedicated to the North American acarologist Roy A. Norton.