The larval and nymphal stases of M. mycotrupetes are described and illustrated, and a discussion of characters unique to this phoretic species is presented. Chief among these are the paranal extensions of the cribrum, the occurrence of five pairs of setae in the J series, and the presence of postepigynial platelets in all postlarval instars. Absence of a bidentate tooth on the movable digit of the female chelicera, and persistent deficiencies in number of tarsal sensilla, are discussed in terms of their possible significance in the evolution of phoresy in M. mycotrupetes.