A membrane between chordotonal organs in the subgenual organ complex of the stick insect Peruphasma schultei.

The subgenual organ complex in stick insects (Phasmatodea) consists of two mechanosensory chordotonal organs, the subgenual organ and distal organ, both located in the haemolymph channel in the tibia of the stick insects. The subgenual organ is a highly sensitive receptor organ for substrate vibrations, which are transferred in the haemolymph channel, while the distal organ has not yet been studied in detail physiologically. The neuroanatomy of the subgenual organ complex is unique to stick insects. A membrane between both organs occurs in different Phasmatodea - Carausius morosus (Sinety), Sipyloidea sipylus (Westwood) and Oreophoetes peruana (Saussure). Between the two sensory organs, the thin membrane is placed horizontally in the tibia. The present study investigates the species Peruphasma schultei (Conle et Hennemann) (Phasmatodea: Pseudophasmatidae: Pseudophasmatinae) from South America (Peru) as a representative of Pseudophasmatinae, a prominent group of neotropical stick insects, for the functional morphology of the chordotonal organs. The aim is to provide insights on the sensory complex from an additional stick insect species and on the similarity of the functional morphology. The present work revealed that in P. schultei the fine membrane occurs in both female and male individuals and in all leg pairs. The membrane was absent in a few leg preparations analysed, in which there was either a close contact or a gap between the subgenual organ and the distal organ. The presence of a membrane connection hints at a coupling between the sensory organs which is presumably also relevant for the mechanosensory functions, indicating that the distal organ may also respond to substrate vibrations. [ABSTRACT FROM AUTHOR]