Effects of sensilla morphology on mechanosensory sensitivity in the crayfish.

Crustaceans contain a great variety of sensilla along their antennules that enable them to sense both hydrodynamic and chemical stimuli in aquatic environments, and can be used to inspire the design of engineered sensing systems. For example, along the antennule of the freshwater crayfish, Procambarus clarkii, four predominant mechanosensory sensilla morphologies are found. To study their response to upstream flow perturbations, atomic force microscopy was utilized to determine P. clarkii sensilla bending in response to an applied force and a mean torsional stiffness, k(t) = 1 × 10(-12) N m degree(-1) was found. A numerical model was developed to quantify the deformation of the four sensilla morphologies due to flow perturbations within their surrounding fluid. These flow perturbations were intended to mimic predator and ambient fluid movements. Results show that upstream fluid motion causes alterations in velocity near the sensilla, accompanied by corresponding variations in pressure along the sensilla surface. The feathered and filamentous sensilla, which are hydrodynamic sensilla, were found to be highly sensitive to flow perturbations. The beaked and asymmetric sensilla, which are bimodal chemo-mechanoreceptors, were found to be much less sensitive to hydrodynamic disturbances. Results also show that sensilla are most sensitive to fluid movement in the along-axis plane of the antennule, with a sharp drop in sensitivity perpendicular to this axis. This sensitivity agrees well with neural responses measured directly from the paired sensory neurons associated with each sensillum. Greater along-axis sensitivity is likely beneficial for determining the direction of fluid movements, which may be important for both aquatic organisms and biomimetic sensing systems.