The development of a new Tasmanian crotoniid species: Crotonia tasmanicasp. nov. is described and illustrated. The morphology of juvenile stages of two Australian moss mites: Crotonia ardala Luxton, 1987 and C. capistrata Luxton, 1987 is also presented. Immature and adult stages of the new species are compared with the most morphologically similar Brazilian species Crotonia camilae Łochyńska, 2008. Although both species possess two pairs of setae c and similar structure of posterior apophyses, there are a number of differences in length and structure of setae.