Developmental morphology of a lyriform organ in the Western black widow (Latrodectus hesperus)

For most spiders, their sensory world is dominated by their ability to detect vibrational stimuli. The organs responsible for detecting substrate vibrations are located on the animals' extremities and known as lyriform organs, close aggregations of membrane-covered slits in the cuticular exoskeleton. The morphology and geometry of the lyriform organ is an important determinant of how it functions and the range of stimuli it can detect. Most work on the morphology, mechanics and physiology of lyriform organs has been conducted on adult wandering spiders, Cupiennius salei, and little is known about the morphology in other species or juveniles. We examine the morphology of the HS10 lyriform organ in both adult and juvenile Western black widows (Latrodectus hesperus). We find hypoallometric scaling of the lyriform organ and the size of individual slits when compared to body size. However, the cuticular pad distal to HS10 scales isometrically across successive instars. We also find an increase in the number of slits within the lyriform organ with each moult. Future work should address physiological responses of the organ across development, which could lead to a better understanding of the function of the cuticular pad and stimuli pertinent to the survival of little-studied juvenile spiders.