Effects of Antennule Morphology and Flicking Kinematics on Flow and Odor Sampling by the Freshwater Crayfish, Procambarus clarkii

The flow structure around the lateral antennular flagellum of the freshwater crayfish, Procambarus clarkii, was quantified to determine how antennule morphology and flicking kinematics affect fine-scale flow surrounding their chemosensory sensilla, called aesthetascs. Particle image velocimetry was used to measure velocity and vorticity of flow between aesthetascs of dynamically scaled physical models of P. clarkii antennules. Results revealed that the spacing between aesthetascs and antennule flicking speed induces substantial changes in fluid flow near aesthetascs. The downstroke flicking motion of the antennule occurs at a peak speed of 2.7cm/s. The returnstroke occurs at approximately 70% of this speed, but the fluid velocity between aesthetascs during the returnstroke is approximately 15% compared with the downstroke. The significant decrease in fluid flow near aesthetascs results from the reduced antennule speed and from the coupled interaction of boundary layers of the aesthetascs and antennule during the returnstroke. Odorant-laden fluid captured during the downstroke is retained between the aesthetascs during the slower returnstroke, and sufficient time occurs for odorant molecules to molecularly diffuse to aesthetasc surfaces. In addition, locally generated vorticity was observed near the tip of the aesthetascs, which may induce odorant transport to aesthetasc surfaces and enhance olfactory response times to odors.