Sperm ultrastructure of Panorpodes kuandianensis (Mecoptera: Panorpodidae)

The sperm ultrastructure of the short-faced scorpionfly Panorpodes kuandianensis Zhong et al. was investigated using transmission electron microscopy. The spermatozoon is composed of a short head containing a bilayered acrosome and an elongate nucleus, a neck transition region, and a long flagellum. The acrosome consists of an acrosomal vesicle and a central perforatorium. The nucleus has two deep, U-shaped lateral grooves and its chromatin contains a series of parallel, regularly arrayed nuclear fibers. The barrel-shaped centriolar adjunct occupies the most volume of the neck region. The flagellum is helical for its whole length and is formed by an axoneme, two mitochondrial derivatives, a pair of accessory bodies, and peculiar accessory structures. The axoneme has nine accessory microtubules at the anterior flagellum region, displaying a 9 + 9 + 2 microtubular pattern, but the accessory microtubules are short and disappear quickly. The two mitochondrial derivatives differ in length and diameter. In the more posterior region, the remaining anchor-shaped mitochondrial derivative has a circular crystalline region, differing from other mecopteran species. The filiform materials are peculiar and lie beside the nucleus and in the flagellum region. Sperm ultrastructural comparison of P. kuandianensis with other families supports a close affinity of Panorpodidae with Panorpidae. In addition, the occurrence of the nine accessory microtubules in the sperm axoneme of Panorpodes indicates that the 9 + 9 + 2 axonemal pattern might be a symplesiomorphy of the Mecoptera.