Many gamasid mites, mainly of the taxon Dermanyssina, possess a secondarily evolved insemination system that is generally described as occurring in two types, the laelapid and the phytoseiid-type, which are structurally considerably different. Considering that Dermanyssina represent the most recent and most diverse group of gamasid mites, it was expected that a greater diversity of insemination system than reflected by the two types could be present and could give an idea of its evolution within the taxon. Here, the authors present a description of the fine-structure of the female secondary insemination system in the dermanyssine mite Hattena cometis. The system consists of a pair of sperm induction pores (solenostomes) and short sperm access ducts (tubules) which end in a syncytium. The syncytial strands of both sides meet medially under the ovary s.str., where they form a spherical syncytial spermatheca. Mature sperm cells of a modified ribbon type were seen in the syncytial parts of the system. The insemination system of Hattena cometis is regarded as a modification of the laelapid type. However, it is much simpler than that of Varroa destructor, the only other gamasid mite with the laelapid type studied ultrastructurally until now, and shows also some structural differences (e.g., no presence of an unpaired sperm duct). Hence, the present study suggests that some intermediate types might be revealed in future ultrastructure studies representing steps in the evolution of the insemination system in the Dermanyssina. J. Morphol. 274:918–925, 2013. © 2013 Wiley Periodicals, Inc.