Silhouettella loricatula (Roewer, 1942)

SPERM TRANSFER FORM (fig. 37): Large, cone-shaped synspermia comprising four sperm. The cytoplasm of the syncytium is heterogeneous and numerous electron-dense plates and droplets, as well as electron-lucent gaps occur (fig. 37A, B). The most obvious characteristic is the distinct, irregular chromatin-condensation pattern (fig. 37B, C). Numerous platelike membrane stacks are visible in the periphery of the sperm conjugate (fig. 37D). A thin homogeneous secretion sheath (, 100 nm) surrounds each sperm conjugate (fig. 37A, B, D).

SPERMATOZOA (fig. 37): Acrosomal complex: AV cylindrical. AF originates from the subacrosomal space and extends into the nuclear canal. Nucleus: prcN elongated, characterized by a conspicuous irregular chromatin-condensation pattern (fig. 37 A– C) and a very small implantation fossa that contains only the two centrioles (fig. 37B). peN not visible in mature sperm; NC located in the periphery (fig. 37C), but empty for the most part (fig. 37C). Axoneme: 9+3 microtubular pattern.

NOTES ON SPERMIOGENESIS (fig. 38): The anterior portion of the prcN is deeply indented and surrounds the AV (fig. 38A, B) in addition to a little electron-dense material (fig. 38B). Besides the AF the subacrosomal space contains some granular material (fig. 38B). The chromatin starts condensation around the nuclear canal (fig. 38C, D) before the characteristic chromatin-condensation pattern is formed (fig. 38 F). While the nucleus elongates and the chromatin starts to condense, a small dropletlike elongation of the nucleus is formed (fig. 38E). This peN probably disintegrates in further development. The implantation fossa is very small and contains only the two centrioles (fig. 38F). Neither the centrioles nor the axoneme (fig. 38F inset) are surrounded by electron-dense material.