The ultrastructure and functional adaptations of male chelicerae in Hattena cometis Domrow are discussed. In particular, as in many other gamasid mites, males of Hattena use the chelicerae, modified as gonopods, to transfer the sperm into the female. For such purpose, a slender process extending from the movable digit, the spermatodactyl, is mainly involved. The spermatodactyl is provided with a sperm transfer duct; in H.cometis, the dorsal surface bent and fused with the ventral surface forms this duct so that the spermatodactyl appears as a cuticular process, connected somehow with the movable digit, and folded on itself to delimit the sperm transfer tube. The organization and ultrastructure of the spermatodactyl are discussed and compared with other gamasid mites studied so far. J. Morphol., 2013. © 2012Wiley Periodicals, Inc.