Ceratozetes behani sp. nov. from Mongolia and its morphological ontogeny is described and illustrated. It is a cryptic species as adult, similar to C. helenae (Pavlichenko, 1993), but differs distinctly from it by the morphology of juveniles. The adult of C. behani has a similar pattern of the lamellar complex and notogastral setae, and shape of porose areas as C. helenae, but differs from it mainly by having longer setae bv″ and v″ on femur II and slimmer femora III and IV. In contrast, the juveniles of C. behani have most prodorsal and gastronotal setae with long spines, whereas in C. helenae these setae are plumose. Moreover, the larva C. behani has a pygidial shield, whereas that of C. helenae has not. The nymphs of both species have the gastronotal shield, but in C. behani it is uniform, with setal pairs dm, dp and h₁, whereas in C. helenae it is divided in two parts, with one pair (da) and five pairs of setae (dm, dp, and h-series), respectively.