Cuticular and sensory structures on the copulatory apparatus of Rhithrogena semicolorata (Ephemeroptera: Heptageniidae)

Abstract

The male copulatory apparatus of Rhithrogena semicolorata shows paired penis lobes, armed with teeth laterally projected and equipped with ventral titillators. As revealed by observations under scanning and transmission electron microscopy (SEM, TEM), the titillators are unarticulated appendages that lack sensory structures. The presence of two depressions, located inside the female genital apparatus, is coherent with a possible function of the titillators in stabilising the couple at mating. Sensory structures are located ventrally in the distal portion of each penis lobe and consist of two kinds of sensilla: campaniform sensilla and short trichoid sensilla. Both sensilla show an organisation consistent with a mechanosensory function, particularly related to pressure stimulations. The presence of mechanoreceptors in the penis lobes is coherent with the need of the male to receive mechanosensory information about the female position during mating.

Keywords:

• mayflies
• mechanoreceptors
• penis lobes
• sensilla
• ultrastructure
• titillators

Acknowledgements

We express our thanks to Dr Francesco Lapiana for his help in collecting specimens. Research partially supported by FISR MICENA founds.