Longitudinal sections of spermatozoa of R. speculum. A, B Acrosome (a), nucleus (N), axoneme (ax), accessory bodies (ab) and mitochondrial derivatives (md), arrow indicates acrosome and nucleus connection area C nucleus-flagellum transition, showing nucleus (N), mitochondrial derivatives (md), accessory bodies (ab), axoneme (ax), arrow indicates centriole, triangular arrowhead indicates centriolar adjunct D sperm flagellum, showing cristae (arrow) arranged in mitochondrial derivatives (md). Scale bars: 0.5 µm (A, B); 0.1 µm (C, D).