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In the present study, spermatozoon ultrastructure was documented in two species of hangingflies, Bittacus strigosus Hagen (Mecoptera: Bittacidae) and B. stigmaterus Say. Structures considered important to phylogenetic assessment that were observed in B. strigosus and B. stigmaterus included a short bilayered acrosome, elongated nucleus, tube-like glycocalyx, centriole adjunct material, accessory bodies, two mitochondrial derivatives, extra axonemal rods, globular units, and 9+2 arrangement of microtubules in the axoneme. Comparisons were made to Bittacus planus Cheng, which was previously examined by electron microscopy ( Xie and Hua 2010 ). Similarities among the ultrastructural characteristics of the three Bittacus species support the monophyly of this genus. Displacement of a mitochondrial derivative by an accessory body was documented for the first time. This paper includes clarifications on differences between accessory bodies and extra axonemal rods, which are issues important to phylogenetic placement.

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