Sperm ultrastructure of corydalid corydalus diasi navas (megaloptera, neuropterida, insecta) with phylogenetic considerations

Abstract

Spermatozoa of the Megaloptera Corydalus diasi (Corydalidae) showed a two-layered acrosome, similar to Raphidioptera, but different from the acrosomal arrangement in Ascalaphidae, Coniopterygidae and Myrmeleontidae (Neuroptera families) and Sialidae (Megaloptera). Also, the acrosomal shape differs from both Raphidioptera and Neuroptera examined so far. The nucleus is cylindrical with condensed chromatin, resembling the sperm of Sialidae, Raphidioptera and Neuroptera. The transition region of C. diasi does not have the nucleus surrounded by centriolar microtubules, and thus, it differs from Sialidae, whose character has been previously considered a synapomorphy between Megaloptera and Raphidioptera. The flagella analysed here possess a 9 + 9 + 2 axoneme arrangement, two elongated circular mitochondrial derivatives and triangular accessory bodies, which are also reported in Raphidioptera. In summary, there are numerous sperm differences between Corydalidae and Sialidae, besides several characters shared between Corydalidae and Raphidioptera. However, several of these similarities appear to be plesiomorphisms rather than synapomorphies. Additionally, this is the first spermatic description for Corydalidae and the second for Megaloptera order. Therefore, considering the number of genres that comprise this family and the lack of spermiocladistics studies for Corydalidae, we recommended that new studies on the field should be performed to better understand the sperm pattern within the Corydalidae genus