Mechanoreceptors in calanoid copepods: designed for high sensitivity

The mechanoreceptors of the first antennae of Pleuromamma xiphias, a mesope lagic calanoid copepod, are critical for the detection of potential threats . These receptors exceed the physiological performance of other crustacean mechanoreceptors in sensitivity to water velocities as well as in frequency response. A study of these receptors was initiated to elucidate structure- function relationships. Morphologically, the receptors resemble the arthrop od scolopidial organs by the presence of a scolopale tube. However, the rig idity of the copepod receptors greatly exceeds those described for crustace ans and other arthropods. The scolopale tube completely encloses the distal dendrites and it is firmly anchored to the cuticle. Microtubules are organ ized in register and arise from microtubule subfibers associated with cresc ent-shaped rods which extend from the basal body region to the setal socket . The distal dendrites an filled with a large number of cross-linked microt ubules. Termination of the distal dendrites inside the lumen of the setae i s gradual with a firm anchoring to the cuticle. A likely mechanism for mech anotransduction would involve a linkage between individual microtubules and mechano-gated channels in the dendritic membrane. The rigidity probably co ntributes to the high frequency sensitivity, and termination of the dendrit e inside the seta increases the overall sensitivity of these receptors. (C) 2001 Elsevier Science Ltd. All rights reserved.