TEM micrographs of S. yangi sperm neck region. A Longitudinal section of the neck region, showing nucleus (n), centriole (c), granular centriolar adjunct (ca) and mitochondrial derivatives (md) B Cross-section anterior of the neck region, showing nucleus (n) C and D Cross-sections of the mid-neck region, showing nucleus (n) and centriolar adjunct (ca) E Cross-section through the terminal end of neck region, showing an eliptical nucleus (n) and a granular centriolar adjunct (ca) F Cross-section through the terminal end of neck region, showing a nucleus (n) and two mitochondrial derivatives (md) G Magnified longitudinal section of neck region, showing granular centriolar adjunct (ca) next to nucleus (n). Scale bars: 500 nm (A, F, G), 200 nm (B–E).