Features of Tissue Organization in the Female Reproductive System of Acanthocephalus tenuirostris (Palaeacanthocephala, Echinorhynchida)

The histological and ultrafine organization of the female reproductive system of Acanthocephalus tenuirostris (Achmerov et Dombrowskaja-Achmerova 1941) was studied. A fragmented ovary (ovarian balls) is shown to consist of somatic (syncytial) and germinal (symplastic or syncytial) components. Oocytes are separated from the germinal syncytium remaining surrounded by the somatic syncytium, fertilized, and surrounded with a fertilization envelope. Then, most zygotes move into the body lumen and continue developing in a free state; however, some of them may develop inside the ovarian ball for some time and even form the outer element of an embryonic shell (E1) on the surface of the fertilization envelope. The walls of the uterine bell, oviducts, and uterus are found to be formed by a unique two-layer tissue, the outer layer of which is represented by myofilaments, and the inner layer of which is cytoplasm with predominating mitochondria; the formation of intercellular material is characteristic of this tissue. The nuclei of this tissue are characterized by signs of nuclear secretion similar to the nuclei of some muscle cells of the acanthocephalans. The uterine wall is shown to be discontinuous, being represented by several large blocks of similar tissue separated by narrow spaces with intercellular material. Such a structure does not correspond to the existing opinion on the symplastic organization of the uterus.