Spermatozoa of megaloptera and raphidioptera (insecta, neuropteroidea)

Spermatozoa from representatives of two minor insect orders, Sialis lutaria, order Megaloptera, and Raphidia spec., order Raphidioptera, have been examined by electron microscopy. Spermatozoa from both species were seen to have an elongated sperm head and a sperm tail containing axoneme, two mitochondrial derivatives of equal sizes, and two accessory bodies. The acrosome in Sialis has a bilateral symmetry in cross section and is fairly complex in that it has both a thin anterior extra-acrosomal layer, an acrosomal vesicle, and a subacrosomal space. In the acrosomal vesicle there is a filament bundle that makes a U-turn. The centriolar microtubules fray out to surround an attenuated posterior portion of the nucleus. The spermatozoa of Raphidia are very long and thin and have a rather simple acrosome. In this species, too, the microtubules of the centrioles surround the posterior, 1-μm-long, portion of the nucleus. This configuration of the centriolar microtubules is not shared by the other examined insects of the neuropteroid superorder and may be a synapomorphic feature. The data are thus consistent with the opinion that Megaloptera plus Raphidioptera form a sister group to the Neuroptera (Planipennia).