Ultrastructural Observations on Spermatozoa of the Soricidae, with Special Attention to a Subfamily Revision of the Japanese Water Shrew Chimarrogale himalayica

抄録

The sperm morphology of four shrew species, Sorex shinto and Chimarrogale himalayica (Soricinae), and Crocidura dsinezumi and Suncus murinus (Crocidurinae) belonging to the family Soricidae, was studied with the electron microscope. The Japanese water shrew Chimarrogale himalayica has been regarded as belonging to the subfamily Crocidurinae based on the teeth with white-colored tips. Spermatozoa of the Soricidae were characterized by the presence of a conspicuously long middle piece compared with those of other eutherians as far as we know, its outer dense fibers arranged in a horseshoe fashion and well-developed satellite fibers found in association with the inner aspect of fiber Nos. 5 and 6. However, the C. himalayica spermatozoon differed from other crocidurine spermatozoa in size and shape of the head; namely, the former head took a small spatulate shape, but the latter a large shield-like shape. In addition, the C. himalayica spermatozoon possessed an unusually slender, wavy and electron-dense apical body at the tip of the subacrosomal space surrounded by the smooth inner acrosomal membrane and the proximal centriole had a solid lumen filled with electron-dense materials, both of which are characteristic of the Soricidae. However, other crocidurine spermatozoa were devoid of such a peculiar apical body in the subacrosomal space surrounded by the serrated inner acrosomal membrane and the proximal centriole had a fistulous lumen. The evidence presented here strongly indicates that C. himalayica should be moved from the subfamily Crocidurinae to the subfamily Soricinae.