A correlated thin-section freeze-fracture study on plasmalemmal and mitochondrial membrane specializations in the principal piece of spermatozoa from the chilopodan Lithobius forficatus L.

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Spermatozoa of Lithobius forficatus L. are filiform shaped. During spermiogenesis mitochondria come to lie beneath the plasmalemma. In mature spermatozoa, they are spirally oriented. During early spermiogenesis 6- to 9-nm-size particles are seen homogeneously distributed throughout both EF and PF plasmalemmal faces of the principal piece. Later, larger EF-face particles are seen in the principal piece. They are homogeneously distributed and 12–16 nm in size. Subsequently, these large, EF-face particles occur in rows along a groove in the plasmalemma which occurs at the juncture of the spiraling mitochondrial surfaces. Mitochondrial membrane particulate specializations are seen only in mitochondria of mature spermatozoa. These specializations include large, approximately 9 × 24-nm-size particles which extend inward from the outer mitochondrial membrane and similar size and shaped particles composing the cristae. This datum is discussed in terms of the temporal sequence of the occurrence of membrane-associated particles in the plasmalemma and mitochondria during spermiogenesis and their possible function in these spermatozoa.