THE ULTRASTRUCTURE OF THE AFLAGELLATE SPERMATOZOON OF THE FRESHWATER TURBELLARIAN HYDROLIMAX GRISEA (PLATYHELMINTHES: PLAGIOSTOMIDAE) ,

Abstract

1. The structure of the aflagellate, non-axonemal spermatozoön of H. grisea was studied by phase contrast optics and electron microscopy. 2. The gamete is fusiform with a centrally-located, vermiform nucleus surrounded by cytoplasmic alveoli. 3. The alveoli and intra-alveolar inclusions are membrane-bound vesicles and membrane-bound particles, respectively. The latter resemble sperm cytoplasm and are believed to be cytoplasmic extensions into alveoli. 4. The nucleus has an irregular pattern of electron-opaque and electron-lucent areas. In predominantly longitudinal orientation are dark fibers, ca. 95 Å separated by 123 Å, coursing through the opaque and lucent areas of the nucleus. 5. Cortical singlet microtubules are the only microtubular elements in the spermatozoön of Hydrolimax. The array and discernible substructure of the singlets are described from sectioned and PTA-macerated material. The possible role of the singlet microtubules in sperm motility in H. grisea is discussed.