The ionic glands of Raillietiella sp. were investigated ultrastructurally in different ontogenetic stages. Modifications of the ultrastructure, number, and distribution of ionic glands were observed after the invasion of the primary larvae into the invertebrate intermediate host and after the invasion of the infective larvae into the vertebrate final host. On the basis of a comparison of the ultrastructure of ionic glands in Raillietiella sp. with that of other pentastomids described in the literature, a general conformity of pentastomid ionic glands can be stated. We propose a defined nomenclature that is integrated into the complete nomenclature of the pentastomid gland system and summarize the synonyms of the ionic glands. Ultrahistochemical chloride detection by energy-dispersive X-ray analysis shows the function of the ionic glands for chloride regulation. Remarkably, in Raillietiella sp., ionic glands also exist in the female genital system. Ionic glands with two central cells occur in cephalobaenids. The existence of ionic glands in Cephalobaena tetrapoda, which has thus far been doubted, can be proved.