The first description of sperm conjugation in Noteridae (Adephaga: Coleoptera) with information on the male reproductive tract of Liocanthydrus mecespilus Guimarães & Ferreira-Jr, 2015.

This study describes the morphology of the male reproductive system and spermatozoa in the Noteridae by analyzing specimens of Liocanthydrus mecespilus. Currently, detailed data on the morphology of the male reproductive system, sperm, and sperm conjugation in the Adephaga (Coleoptera) are available only for the families Gyrinidae, Carabidae, and Dytiscidae. The male reproductive organs and sperm were analyzed using light and transmission electron microscopy. The reproductive tract comprises a pair of unifollicular testes, a pair of vasa deferentia with a median dilated portion that forms the seminal vesicles, a pair of accessory glands, and an ejaculatory duct. The spermatozoa measured approximately 675 µm in length. They were typically found in pairs, united by an electron-dense material referred to as the head-connective material complex, which was observed at the base of the testes and seminal vesicles. The male reproductive system of this species shares characteristics with those described for other Adephaga. At the same time, the sperm conjugation resembles that found in other Dytiscidae, except for the arrangement of the nuclei in the electron-dense material. This is the first report on sperm conjugation in Noteridae, providing initial insight into their male reproductive system and the morphology of their spermatozoa. These findings may enhance our understanding of the biology of these beetles and their systematic position within the Adephaga suborder.