The foregut of Raillietiella sp. was investigated ultrastructurally in different ontogenetic stages: the embryo prior to hatching, the first-stage larva, the infective fourth-stage larva from the intermediate host, and juveniles and adults from the definitive host. As early as at the embryo stage the chitinous mouth armature is highly specialized. During postembryogenesis this structure is modified until it reaches its final shape in the juvenile. The most important changes occur during the period of development from the infective larva to the juvenile, which is related to the change from the intermediate to the definitive host; only stages inhabiting the definitive host can use their mouth as a suction pump. Therefore, only juveniles and adults are capable of sucking blood, whereas larvae are dependent on accessible liquid food. The remaining foregut represents a conveyor tube, growing in width toward the midgut. From the juvenile stage onward the transition to the midgut is formed as a cardiac valve.

The midgut cells of cephalobaenid pentastomids contain spherocrystals varying in size and appearance between the genera. Iron was detected in the vicinity of the crystals in all three genera, being considerably fainter in Reighardia sternae than in the other species. Ultrastructurally a distinct lamination of the spherocrystals was evident, being faint in R. sternae but clearly expressed in Raillietiella hemidactyli and Cephalobaena tetrapoda. According to the species, their diameter ranged from 1.3 to 6.25 microns. The size and number of the crystals were highest in R. hemidactyli and lowest in R. sternae. The inclusions were formed in the endoplasmic reticulum and migrated toward the cellular apex, accumulating there and being expelled into the midgut lumen. As determined by energy-dispersive X-ray analysis, calcium turned out to be the main component of the crystals. Furthermore, small amounts of chlorine and iron could be traced in the crystals. The relevance of the crystals is regarded as a kind of storage excretion such as that present in many other arthropods.

The "Dorsalorgan" of pentastomids is an embryonic gland. With respect to a general revision of the glandular equipment of pentastomids and its synonyms the term embryonic gland, first mentioned by Esslinger in 1968, or glandula embryonalis (original) appears to be most suitable. Thus, this terminology may no longer lead to confusion of these glands with dorsal organs of other arthropods. The ultrastructure of the embryonic gland and its role within the development of the embryonic envelopes of the pentastomid genus Raillietiella is described herein for the first time. The embryonic gland is composed of numerous secretory cells, which are arranged concentrically around a bottle-shaped cavity. The cells of the neck region produce an extracellular supporting layer to stabilize the collar. The basal cells are characterized by numerous microvilli, secreting mucus into the cavity. The product of the embryonic gland is secreted between the zona radiata externa/interna and the blastoderm cuticle, respectively. The embryonic gland disintegrates before larval hatching.

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The midgut of Raillietiella sp. was investigated in different ontogenetic stages. The developing embryo, the hatched first-stage larva, the infective fourth-stage larva from the intermediate host, and juveniles and adults from the definitive host were viewed ultrastructurally. From the fourth-stage larva onward, spherocrystals were visible in the midgut cells. They contained only small amounts of calcium and iron, depending on the ontogenetic stage. The cycle of crystal formation and destruction or excretion, respectively, is described herein. Their role in ion regulation and excretion is discussed with regard to similar inclusions in other arthropods.