Investigation of different ontogenetic stages of Raillietiella sp. (Pentastomida:Cephalobaenida): the embryonic gland--glandula embryonalis--or dorsalorgan.

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.