Fig. 3

Transmission and scanning electron micrographs revealed structural morphology of pangolin spermatozoa. a With sperm smear analysis, we showed pangolin sperm exhibited rod-shaped sperm head structure similar to that of avian species. The average length of pangolin sperm was for 60.7 ± 6.8 μm with 10.4 ± 1.1 (with 1 ± 0.2 in width), 9.9 ± 1.4, 40.4 ± 5.8 μm measured for sperm head, mid-piece and tail, respectively. b Transmission electron microscopy confirmed a triangle-shaped structure at the tip of rod-shaped sperm head with a commonly observed 9 + 2 axoneme arrangement; moreover, mitochondria were also observed at the mid-piece adjacent to plasma membrane. Apparent fibrous sheath replaced mitochondria surrounded the axoneme can also be observed at the distal principal piece of sperm tail. c Scanning electron micrographs showed distinct sperm head (C1), sperm head to mid-piece junction (C2) and sperm tail (C3). Besides, an unexpected round-shaped sperm morphology (marked with arrowheads) was also detected occasionally. Ar: acrosome, n: nucleus, df: dense fiber; a: axoneme; mt: mitochondria; p: plasma membrane; fs: fibrous sheath. Representative images were presented