Insect evolution toward aquatic habitats; reassessment of antennal sensilla in the water bug families Ochteridae, Gelastocoridae and Aphelocheiridae (Hemiptera: Heteroptera: Nepomorpha)

The first comparative morphology study on antennal sensilla of Ochteridae, Gelastocoridae and Aphelocheiridae, carried out with the use of a scanning electron microscope, is provided. Our research hypothesis was: the antennal sensilla of the studied families reflect their different adaptations for use in aquatic habitats, while maintaining a common set of sensilla similar to other water bugs (Nepomorpha). Therefore, the number and placement of antennal sensilla of several species in the mentioned families were studied using scanning electron microscopy. Nine main types of mechano- chemo- and thermo-hygroreceptive sensilla were confirmed on their surface, including sensilla trichodea, chaetica, club-like, campaniformia, basiconica, coeloconica, plate-like, ampullacea and sensilla placodea multilobated. While seven of these were already documented in other species, two of them (sensilla plate-like and placodea multilobated) were yet to be documented on the antennae of Nepomorpha. All families display differences in the shape and length of antennae as well as among sensilla types. These findings support our hypothesis regarding differences in sensillar structures among families adapted differently to suitable niches. Differences between these families and previously studied nepomorphan taxa (Nepoidea) were also documented. However, the general set of sensilla observed on the antennae of the studied species is very similar to the one documented in Nepoidea. Therefore, we confirmed our assumptions regarding similarities in antennal sensilla between the studied families and other nepomorphan insects.