Meeting Abstract

106.2  Saturday, Jan. 7  Fluid dynamics of antennule flicking of the terrestrial hermit crab, Coenobita rugosus (Decapoda: Anomura) WALDROP, LD; Univ. of California, Berkeley lwaldrop@berkeley.edu

Many marine decapod crustaceans sense chemical signals (odors) in their surroundings to find food and mates using first antennae (antennules) which bear arrays of chemosensory hairs (aesthetascs). The fluid dynamics of discrete odor sampling are well studied in several marine species (spiny lobster, blue crab, Oregon shore crab), but odor-sampling fluid dynamics are unstudied in their air-dwelling relatives the coenobitid hermit crabs, which live their entire adult lives on land. Despite an evolutionary shift from sea to land which dramatically changes the fluid environment in which olfaction occurs, terrestrial hermit crabs retain many features of marine crabs including aesthetasc-bearing antennules. Compared to marine crabs, the antennules of terrestrial hermit crabs are heavily modified, having arrays of short, leaf-like aesthetascs that partially overlap. Terrestrial hermit crabs also move their antennules back and forth in a motion similar to the antennule movement of marine crabs. To investigate how this evolutionary transition affected the fluid dynamics of antennule flicking, I examined the kinematics of antennule flicking by filming hermit crabs (Coenobita rugosus) and the antennule morphometrics by collecting their antennules for scanning electron microscopy. Using these data, a dynamically scaled physical model of the antennule was constructed, and particle image velocimetry (PIV) was used to measure fluid flow around the model. PIV results indicate that although terrestrial hermit crabs have homologous antennule movements and morphological features with marine crabs, they do not discretely sample odors. Flicking by terrestrial hermit crabs could serve to increase the probability of encountering odors in turbulent air flow.