Studies on the fine structure of the mitochondrial derivative in spermatozoa of a gastropod.

Spermatozoa of Limax sp. were studied by electron microscopy following thin section and freeze-fracture techniques. Mature spermatozoa were seen to be helically shaped, 150 microns long cells. A single mitochondrion extends the entire length of the spermatozoon. Its helical turn is the same as that of the spermatozoon. Freeze-fracture images of the spermatozoon reveal that the EF and PF, plasmalemmal faces contain scattered, 7-9 nm size particles, and that the PF, outer mitochondrial membrane face contains 8-10 nm size particles. The corresponding EF, outer mitochondrial face contains matching pits. A paracrystalline complex is situated between the inner and outer mitochondrial membranes. The complex is constructed of a series of 8-9 nm thick, 35 nm wide, helically orientated, tripartate elements which extend the full length of the spermatozoon. The helical tilt angle is approximately 55 degrees. Each element is composed of tightly approximated (interspace distance 10 nm), strands of particles 8-9 nm in diameter. Speculations as to the significance of this complex, and its location between inner and outer mitochondrial membranes are made. It is concluded that the paracrystalline order of the complex either reflects the molecular packing of enzyme systems present in the mitochondrion, or some other unknown function.