The sperm structure and spermiogenesis of the heteropteran Coptosoma scutellatum (Geoffroy) with emphasis on the development of the centriole adjunct

•The sperm structure of the uncommon heteroptera Coptosoma scutellatum is described.•During spermiogenesis an extensive centriole adjunct material is produced.•Such a centriole adjunct is a MTOC (microtubule-organizing-center).•In the mature sperm the centriole adjunct is transformed in a dense, compact material.

The sperm structure and spermiogenesis of the morphologically peculiar heteropteran Coptosoma scutellatum has been examined with electron microscopy. The sperm has a short monolayer acrosome, a cylindrical nucleus, a 9 + 9 + 2 axoneme and two mitochondrial derivatives with crystallized matrix. It shows the synapomorphies typical of the group, consisting of (a) two crystallized areas in the mitochondrial derivatives; (b) the presence of two bridges connecting the intertubular material of the flagellar axoneme to the flattened cisterns adhering to the inner sides of the mitochondrial derivatives; (c) the absence of accessory bodies. The most interesting feature is the presence, in the early spermatid, of an extended centriole adjunct material with the shape of a large ribbon-like structure. This material surrounds the posterior nuclear region and extends anteriorly along the nucleus. It is a microtubule-organizing-center (MTOC) producing the many microtubules surrounding the sperm components At the end of spermiogenesis, the centriole adjunct material modifies into two kidney-like structures accompanying the nuclear posterior end and surrounding the modified centriole.